U.S. patent application number 13/231878 was filed with the patent office on 2012-01-19 for thin film semiconductor-on-glass solar cell devices.
This patent application is currently assigned to TRANSLUCENT INC.. Invention is credited to Petar Atanackovic.
Application Number | 20120012166 13/231878 |
Document ID | / |
Family ID | 40131203 |
Filed Date | 2012-01-19 |
United States Patent
Application |
20120012166 |
Kind Code |
A1 |
Atanackovic; Petar |
January 19, 2012 |
Thin Film Semiconductor-on-Glass Solar Cell Devices
Abstract
The present invention relates to semiconductor devices suitable
for electronic, optoelectronic and energy conversion applications.
In a particular form, the present invention relates to the
fabrication of a thin film solar cells and thin film transistors
through the advantageous combination of semiconductors, insulators,
rare-earth based compounds and amorphous and/or ceramic and/or
glass substrates. Example embodiments of crystalline or
polycrystalline thin film semiconductor-on-glass formation using
rare-earth based material as impurity barrier layer(s) are
disclosed. In particular, thin film silicon-on-glass substrate is
disclosed as the alternate embodiment, with impurity barrier
designed to inhibit transport of deleterious alkali species from
the glass into the semiconductor thin film.
Inventors: |
Atanackovic; Petar; (Palo
Alto, CA) |
Assignee: |
TRANSLUCENT INC.
Palo Alto
CA
|
Family ID: |
40131203 |
Appl. No.: |
13/231878 |
Filed: |
September 13, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12119387 |
May 12, 2008 |
8071872 |
|
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13231878 |
|
|
|
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60944369 |
Jun 15, 2007 |
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Current U.S.
Class: |
136/252 |
Current CPC
Class: |
Y02E 10/50 20130101;
H01L 31/1055 20130101; C03C 17/3642 20130101; C03C 17/3678
20130101; C03C 17/3636 20130101; H01L 31/03921 20130101; C03C 17/36
20130101 |
Class at
Publication: |
136/252 |
International
Class: |
H01L 31/02 20060101
H01L031/02 |
Claims
1. A device for converting radiation to electrical energy
comprising; an active layer for the converting radiation to
electrical energy comprising a first semiconductor layer of first
conductivity type of thickness between about 30 nm and 150 nm; a
second semiconductor layer of second conductivity type of thickness
between about 30 nm and 150 nm; a transparent barrier layer
consisting of one or more rare earth compounds; and a substrate
transparent to a majority of the radiation for converting, wherein
the barrier layer separates the active layer and the substrate such
that migration of deleterious species across the barrier layer is
functionally impeded and wherein the first and second semiconductor
layers comprise one or more layers chosen from a group consisting
of germanium carbide (GeC.sub.x), germanium nitride (GeN.sub.x),
tin germanium (SnGe.sub.x), tin oxide (SnO.sub.x), gallium
phosphide (GaP), gallium nitride (GaNx), indium nitride (InNx),
aluminium nitride (AlNx), zinc oxide (ZnO.sub.x), magnesium oxide
(MgO.sub.x) and Si.sub.vSn.sub.yGe.sub.zC.sub.w or combinations and
non-stoichiometric combinations thereof wherein 0<x.ltoreq.20
and 0<v, y, z.ltoreq.1 and 0.ltoreq.w.ltoreq.1.
2. A device as in claim 1 wherein the barrier layer comprises at
least two layers wherein at least one of the at least two layers
has a band gap greater than about 3 eV.
3. A device as in claim 1 wherein the transparent barrier layer
comprises a first and second layer wherein the first layer is in
contact with the transparent substrate and wherein the first layer
or second layer consists of one or more compounds chosen from a
group consisting of calcium oxide (CaO), sodium oxide (Na.sub.2O),
potassium oxide (K.sub.2O), aluminum oxide (Al.sub.2O.sub.3), boron
oxide (B.sub.2O.sub.3), zirconium oxide (ZrO.sub.2), zircon
(ZrSiO.sub.4), lead oxide (PbO), alkaline earth metal oxides
(AEOx), phosphate glass, phosphorous silicate glass, rare-earth
sesquioxide (RE.sub.2O.sub.3), rare-earth dioxide (REO.sub.2),
rare-earth monoxide (REO), rare-earth nitride (REN), rare-earth
oxynitride (REO.sub.xN.sub.y), rare-earth phosphide (REP),
rare-earth oxyphosphide (REO.sub.xP.sub.y), rare-earth carbide
(REC.sub.y), rare-earth oxycarbide (REO.sub.xC.sub.y), aluminum
rare-earth oxide (RE.sub.xAl.sub.yO.sub.w), rare-earth
aluminosilicate (RE.sub.xAl.sub.ySi.sub.zO.sub.w), silicon nitride
(SiN.sub.x), (Si.sub.xAl.sub.yN.sub.z), N:Al.sub.2O.sub.3, aluminum
oxynitride (AlO.sub.xN.sub.y), aluminum nitride (AlN.sub.x),
silicon-aluminum-oxynitride (Si.sub.zAl.sub.yO.sub.xN.sub.y),
silicon-carbon-nitride (Si.sub.zC.sub.xN.sub.y),
aluminum-carbon-oxynitride (Al.sub.zC.sub.vO.sub.xN.sub.y),
SiO.sub.x, rare-earth material, mixtures of silicon-germanium and
combinations and non-stoichiometric combinations thereof.
4. A device as in claim 1 wherein the transparent barrier layer
comprises a first and second layer wherein the first layer is in
contact with the transparent substrate and wherein the first layer
or second layer consists of one or more compounds chosen from a
group consisting of
[RE].sub.x[RE].sub.y[RE].sub.z[C].sub.m[O].sub.n[N].sub.p[P].sub.r[Si].su-
b.s[Ge].sub.t[Al].sub.u wherein x>0 and at least one of y, z, m,
n, p, r, s, t, or u are >0 and RE is a rare earth.
5. A device as in claim 1 wherein the transparent substrate is
chosen from a group consisting of sapphire, aluminum oxide
(Al.sub.2O.sub.3), diamond (C.sub.4), calcium fluoride (CaF.sub.2),
zircon (Zr.sub.xSi.sub.1-xO.sub.4), zinc oxide (ZnO), aluminum
nitride (AlN), glass, sodium-silicate glass
(Na.sub.2O).sub.x.(SiO.sub.2).sub.1-x, alkali-metal oxides
(AMO.sub.x), alkaline-earth metal oxides, a ceramic and
crystallised bauxite.
6. A device for converting radiation to electrical energy
comprising; an active layer for the converting radiation to
electrical energy comprising a first semiconductor layer of first
conductivity type of thickness between about 30 nm and 150 nm; a
second semiconductor layer of second conductivity type of thickness
between about 30 nm and 150 nm; a transparent barrier layer
consisting of one or more rare earth compounds; and a substrate
transparent to a majority of the radiation for converting, wherein
the barrier layer separates the active layer and the substrate such
that migration of deleterious species across the barrier layer is
functionally impeded and wherein the first and second semiconductor
layers comprise one or more layers chosen from a group consisting
of In.sub.xGa.sub.yAl.sub.zN.sub.w and non-stoichiometric
combinations thereof wherein 0<w, y.ltoreq.1 and 0.ltoreq.x,
z.ltoreq.1.
7. A device as in claim 6 wherein the barrier layer comprises at
least two layers wherein at least one of the at least two layers
has a band gap greater than about 3 eV.
8. A device as in claim 6 wherein the transparent barrier layer
comprises a first and second layer wherein the first layer is in
contact with the transparent substrate and wherein the first layer
or second layer consists of one or more compounds chosen from a
group consisting of calcium oxide (CaO), sodium oxide (Na.sub.2O),
potassium oxide (K.sub.2O), aluminum oxide (Al.sub.2O.sub.3), boron
oxide (B.sub.2O.sub.3), zirconium oxide (ZrO.sub.2), zircon
(ZrSiO.sub.4), lead oxide (PbO), alkaline earth metal oxides
(AEOx), phosphate glass, phosphorous silicate glass, rare-earth
sesquioxide (RE.sub.2O.sub.3), rare-earth dioxide (REO.sub.2),
rare-earth monoxide (REO), rare-earth nitride (REN), rare-earth
oxynitride (REO.sub.xN.sub.y), rare-earth phosphide (REP),
rare-earth oxyphosphide (REO.sub.xP.sub.y), rare-earth carbide
(REC.sub.y), rare-earth oxycarbide (REO.sub.xC.sub.y), aluminum
rare-earth oxide (RE.sub.xAl.sub.yO.sub.w), rare-earth
aluminosilicate (RE.sub.xAl.sub.ySi.sub.zO.sub.w), silicon nitride
(SiN.sub.x), (Si.sub.xAl.sub.yN.sub.z), N:Al.sub.2O.sub.3, aluminum
oxynitride (AlO.sub.xN.sub.y), aluminum nitride (AlN.sub.x),
silicon-aluminum-oxynitride (Si.sub.zAl.sub.yO.sub.xN.sub.y),
silicon-carbon-nitride (Si.sub.zC.sub.xN.sub.y),
aluminum-carbon-oxynitride (Al.sub.zC.sub.vO.sub.xN.sub.y),
SiO.sub.x, rare-earth material, mixtures of silicon-germanium and
combinations and non-stoichiometric combinations thereof.
9. A device as in claim 6 wherein the transparent barrier layer
comprises a first and second layer wherein the first layer is in
contact with the transparent substrate and wherein the first layer
or second layer consists of one or more compounds chosen from a
group consisting of
[RE].sub.x[RE].sub.y[RE].sub.z[C].sub.m[O].sub.n[N].sub.p[P].sub.r[Si].su-
b.s[Ge].sub.t[Al].sub.u wherein x>0 and at least one of y, z, m,
n, p, r, s, t, or u are >0 and RE is a rare earth.
10. A device as in claim 6 wherein the transparent substrate is
chosen from a group consisting of sapphire, aluminum oxide
(Al.sub.2O.sub.3), diamond (C.sub.4), calcium fluoride (CaF.sub.2),
zircon (Zr.sub.xSi.sub.1-xO.sub.4), zinc oxide (ZnO), aluminum
nitride (AlN), glass, sodium-silicate glass
(Na.sub.2O).sub.x.(SiO.sub.2).sub.1-x, alkali-metal oxides
(AMO.sub.x), alkaline-earth metal oxides, a ceramic and
crystallised bauxite.
11. A device for converting radiation to electrical energy
comprising; an active layer for the converting radiation to
electrical energy comprising a first semiconductor layer of first
conductivity type of thickness between about 30 nm and 150 nm; a
second semiconductor layer of second conductivity type of thickness
between about 30 nm and 150 nm; a transparent barrier layer
consisting of one or more rare earth compounds; and a substrate
transparent to a majority of the radiation for converting, wherein
the barrier layer separates the active layer and the substrate such
that migration of deleterious species across the barrier layer is
functionally impeded and wherein the first and second semiconductor
layers comprise one or more layers chosen from a group consisting
of Zn.sub.xMg.sub.yO.sub.zN.sub.w and non-stoichiometric
combinations thereof wherein at least one of x or y is >0 and at
least one of z or w is >0.
12. A device as in claim 11 wherein the barrier layer comprises at
least two layers wherein at least one of the at least two layers
has a band gap greater than about 3 eV.
13. A device as in claim 11 wherein the transparent barrier layer
comprises a first and second layer wherein the first layer is in
contact with the transparent substrate and wherein the first layer
or second layer consists of one or more compounds chosen from a
group consisting of calcium oxide (CaO), sodium oxide (Na.sub.2O),
potassium oxide (K.sub.2O), aluminum oxide (Al.sub.2O.sub.3), boron
oxide (B.sub.2O.sub.3), zirconium oxide (ZrO.sub.2), zircon
(ZrSiO.sub.4), lead oxide (PbO), alkaline earth metal oxides
(AEOx), phosphate glass, phosphorous silicate glass, rare-earth
sesquioxide (RE.sub.2O.sub.3), rare-earth dioxide (REO.sub.2),
rare-earth monoxide (REO), rare-earth nitride (REN), rare-earth
oxynitride (REO.sub.xN.sub.y), rare-earth phosphide (REP),
rare-earth oxyphosphide (REO.sub.xP.sub.y), rare-earth carbide
(REC.sub.y), rare-earth oxycarbide (REO.sub.xC.sub.y), aluminum
rare-earth oxide (RE.sub.xAl.sub.yO.sub.w), rare-earth
aluminosilicate (RE.sub.xAl.sub.ySi.sub.zO.sub.w), silicon nitride
(SiN.sub.x), (Si.sub.xAl.sub.yN.sub.z), N:Al.sub.2O.sub.3, aluminum
oxynitride (AlO.sub.xN.sub.y), aluminum nitride (AlN.sub.x),
silicon-aluminum-oxynitride (Si.sub.zAl.sub.vO.sub.xN.sub.y),
silicon-carbon-nitride (Si.sub.zC.sub.xN.sub.y),
aluminum-carbon-oxynitride (Al.sub.zC.sub.vO.sub.xN.sub.y),
SiO.sub.x, rare-earth material, mixtures of silicon-germanium and
combinations and non-stoichiometric combinations thereof.
14. A device as in claim 11 wherein the transparent barrier layer
comprises a first and second layer wherein the first layer is in
contact with the transparent substrate and wherein the first layer
or second layer consists of one or more compounds chosen from a
group consisting of
[RE].sub.x[RE].sub.y[RE].sub.z[C].sub.m[O].sub.n[N].sub.p[P].sub.r[Si].su-
b.s[Ge].sub.t[Al].sub.u wherein x>0 and at least one of y, z, m,
n, p, r, s, t, or u are >0 and RE is a rare earth.
15. A device as in claim 11 wherein the transparent substrate is
chosen from a group consisting of sapphire, aluminum oxide
(Al.sub.2O.sub.3), diamond (C.sub.4), calcium fluoride (CaF.sub.2),
zircon (Zr.sub.xSi.sub.1-xO.sub.4), zinc oxide (ZnO), aluminum
nitride (AlN), glass, sodium-silicate glass
(Na.sub.2O).sub.x.(SiO.sub.2).sub.1-x, alkali-metal oxides
(AMO.sub.x), alkaline-earth metal oxides, a ceramic and
crystallised bauxite.
Description
PRIORITY
[0001] This application is a continuation of U.S. application Ser.
No. 12/119,387, filed on May 12, 2008 and claims priority from
Provisional application 60/944,369 filed on Jun. 15, 2007.
CROSS REFERENCE TO RELAYED APPLICATIONS
[0002] Applications and patent Ser. Nos. 09/924,392, 10/666,897,
10/825,912, 10/825,974, 11/025,363, 11/025,681, 11/025,692,
11/025,693, 11/084,486, 11/121,737, 11/187,213, 11/053,775,
11/053,785, 11/054,579, 11/068,222, 11/188,081, 11/253,525,
11/254,031, 11/393,629, 11/398,910, 11/472,087, 11/788,153,
11/960,418, 12/119,387, 60/820,438, 60/811,311, 60/847,767,
60/905,419, 60/905,945, 60/944,369, 60/949,753, U.S. Pat. No.
7,018,484, U.S. Pat. No. 7,037,806, U.S. Pat. No. 7,135,699, U.S.
Pat. No. 7,199,015, all held by the same assignee, contain
information relevant to the instant invention and are incorporated
herein in their entirety by reference. References, noted at the
end, are incorporated herein in their entirety by reference.
BACKGROUND OF THE INVENTION
[0003] Prior art concerning solar cells and thin film transistors,
TFTs, are known to one knowledgeable in the art. References
contained in U.S. Pat. No. 4,128,733, U.S. Pat. No. 6,743,974, U.S.
Pat. No. 7,030,313, U.S. 2002/0040727, U.S. 2005/0000566 are cited
as prior art and incorporated herein in their entirety by
reference. The present invention addresses the need to increase
solar cell efficiency and to further reduce cost over prior art
techniques.
[0004] Typically, the use of low cost substrates places limitation
upon thin film semiconductor crystal quality and/or thermal budget
required for thin film deposition method of a thin film(s). Low
thermal budget deposition of thin films typically results in poor
crystal quality semiconductors realized upon amorphous glass
substrates. Single semiconductor crystals may nucleate in localized
areas upon an initial glass substrate surface, but formation of
homogeneous and long range crystal order within the thin film
across substantially the entire large area glass substrate is
practically impossible without complex post growth
recrystallization. Even so, the film quality attained using prior
art complex recrystallization techniques is still inferior to bulk
single crystal growth techniques, such as, the Czochralski crystal
growth (CZ) method.
[0005] Single crystal thin film epitaxy is typically done on
substrates with intrinsic properties of high single crystal
quality, atomically flat surface, and low crystal structure
mismatch between the film and substrate. More desirable of the
polycrystalline forms are thin film semiconductors exhibiting large
domains (grain size .about.0.1-10 microns) in lateral and/or
vertical dimensions relative to the film growth direction. Thin
films exhibiting larger lateral grain dimension than film thickness
enable advantageous transport of electronic carriers parallel to
the film/substrate surface. Direct deposition of thin film
semiconductors onto glass substrates without complex post
processing results in polycrystalline (pc), microcrystalline (mc),
nanocrystalline (nc) and/or amorphous (a) semiconductor thin
films.
BRIEF SUMMARY OF THE INVENTION
[0006] The present invention relates to semiconductor devices
combined with an inexpensive substrate for electronic and
optoelectronic applications. In a particular form the present
invention relates to fabrication of a solar cell and/or thin film
transistor (TFT) through the combination of rare-earth metal,
rare-earth metal-oxides-nitrides, -phosphides and -carbides and
Group IV, III-V, and II-VI semiconductors and alloys disposed upon
inexpensive substrates, such as glass. In an embodiment, thin film
semiconductor materials composed of silicon (Si) and/or germanium
(Ge) are disposed upon cost effective silicon dioxide (SiO.sub.2)
based glass substrate. Such semiconductor-on-glass (SoG) articles
are applicable to thin film transistor and solar cell manufacture.
The present invention discloses the use of a functional barrier
layer disposed between a thin film semiconductor layer and an
inexpensive substrate so as to inhibit transport and deleterious
action of impurity species migrating from the substrate into a thin
film semiconductor, thereby degrading the electronic and/or optical
performance of the said device. Optionally, a functional barrier
layer may serve as an alternative barrier between an inexpensive
substrate and a functional device disposed thereon; examples of
types of barriers are thermal, mechanical, chemical, optical,
and/or other radiation deleterious to a functional device and/or
from a device to its substrate.
[0007] Thin film semiconductor-on-glass application to solar cell
and TFT devices benefit from the insulating nature of the glass
substrate and can be designed as ideal thin film
semiconductor-on-insulator (SOI) structures. For mass manufacture
of SoG the utility of a glass substrate is primarily due to the
potential low cost of alkali-silicate glasses. However, it has long
been known by workers in the field of glass manufacture that most
compositions of alkali-silicate glasses exhibit some electrical
conductivity. The electrical activity of the alkaline-silicate
glasses is directly attributable to mobile positive alkaline ions
through the silicate network; in addition inexpensive glasses may
contain high levels of boron, lead and other elements injurious to
a semiconductor. Optional inexpensive substrates contain
alternative elements not acceptable to a solid-state device; in
general some type of barrier must isolate a semiconductor device
from some property of an inexpensive substrate.
[0008] It is an object of one embodiment of the present invention
to fully utilize the low cost of alkaline-silicate glasses for use
in SoG and increase the performance of devices formed by use of
alkaline barrier layers. An example embodiment, but not limited to,
is the use of rare-earth compound(s), such as a rare-earth oxide
(REO.sub.x), comprising charged oxygen vacancies (O.sub.v.sup.n)
capable of neutralizing the migration of deleterious positive
alkaline ions, such as Na.sup.+ and/or K.sup.+, into a
semiconductor active region; charged oxygen vacancies
(O.sub.v.sup.n) functionally impede migration of positive ions to
the extent that an active region above a barrier layer functions
within specification.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0009] FIG. 1A depicts schematically the physical MOS layer
structure formed on a SoG substrate and FIG. 1B depicts the energy
band structure of the MOS SoG device as a function of
cross-sectional distance vertically through the layers.
[0010] FIG. 2A shows the use of a barrier layer in a modified MOS
SoG structure; FIG. 2B, shows a criteria for an alkali barrier
layer which is the advantageous partitioning of the valence
(.DELTA.E.sub.v) and conduction (.DELTA.E.sub.c) band.
[0011] FIG. 3 shows the geometry used for ion implantation of
foreign species into preferentially CZ Si substrate.
[0012] FIG. 4 shows depth profiles for H+ ions using various
incident energy implants.
[0013] FIG. 5 shows exemplary ion implantation into an original
device substrate.
[0014] FIG. 6 shows exemplary ion implantation into an original
device substrate.
[0015] FIG. 7 shows the distribution of H.sup.+ ions 701 in the
buried layer beneath the Si surface for the case of 3 MeV.
[0016] FIGS. 8A and B show individual parallel process paths for
fabrication of thin film single crystal solar cell on glass
article.
[0017] FIGS. 9A and B show how an alternative or replacement
substrate with insulating and/or conductive barrier layers and
implanted CZ Si substrate are joined together.
[0018] FIGS. 10A and B show how a compound multilayer article is
subjected to a thermal annealing sequence.
[0019] FIG. 11 shows how, with application of external mechanical
stimulus to at least one region of the edge of the compound
article, the fracture propagates throughout the defect plane.
[0020] FIG. 12 shows how a wafer bonded thin film CZ Si forms a
buried barrier layer on a glass substrate and are then processed to
form a vertical type MIS.
[0021] FIG. 13 discloses an example method and general process flow
for fabricating multiple single crystalline semiconductor
layers.
[0022] FIG. 14 shows a remaining portion of a silicon thin film
separated from the bulk of a substrate via defect layer.
[0023] FIG. 15 shows a transferred layer stack forming a p-i-n-i-p
doped Si multilayer diode coupled to a glass substrate.
[0024] FIG. 16A shows the overlap of Ge absorption with the solar
spectrum and 16B shows the energy band structure of bulk single
crystal Si as a function of energy.
[0025] FIG. 17A shows a metal-insulator-semiconductor (MIS) device
fabricated upon a glass substrate; FIG. 17B shows an equivalent
circuit.
[0026] FIG. 18A shows multiple lateral devices connected via a
common active layer contact; FIG. 18B shows an equivalent
circuit.
[0027] FIG. 19A is an p-i-n SoG embodiment; FIG. 19B shows an
equivalent circuit.
[0028] FIG. 20A shows multiple lateral p-i-n devices fabricated
across the SoG substrate;
[0029] FIG. 20B shows p-i-n devices series connected.
[0030] FIG. 21A is a stacked layer structure consisting of two
p-i-n diodes comprising different intrinsic absorber thicknesses.
FIG. 21B shows the generation rate G (.lamda., z) of electron-hole
pairs as a function of vertical distance, z, through a layered
structure.
[0031] FIGS. 22A and 22B show wavelength bands 2300 & 2310 used
for an example tandem Si: p-i-n-p-i-n solar cells.
[0032] FIG. 23 discloses a MIS/PIN hybrid.
[0033] FIG. 24A: Process steps for epitaxial deposition of single
crystal article containing thin film semiconductor and sacrificial
layer.
[0034] FIG. 24B: Selective modification of sacrificial layer via
lateral process.
[0035] FIG. 24C: Transformation of single crystal sacrificial layer
via selective process.
[0036] FIG. 25A: Process of forming single crystal article
comprising thin film semiconductor and sacrificial layer. Parallel
process of preparing alternative substrate for wafer bonding to
exposed thin film semiconductor or interfacial bonding layer
surface.
[0037] FIG. 25B: Process steps of wafer bonding alternative
substrate to single crystal article.
[0038] FIG. 25C: Process steps showing selective lateral
modification of sacrificial layer contained in composite
article.
[0039] FIG. 26: Process paths for thin film semiconductor layer
separation by action of sacrificial layer in composite article.
[0040] FIG. 27: Chemical processes for modifying crystal structure
of single crystal rare-earth oxide by means of hydrogenation,
carbonization and hydration.
[0041] FIG. 28: Catalytic layer separation using rare-earth based
layer comprising alternative substrate and thin film semiconductor
layer.
[0042] FIG. 29: Crystal structure modification of process using
rare-earth based compound.
[0043] FIG. 30: Single crystal rare-earth based sacrificial layer
under selective etching or removal via incident species, ultimately
leaving the exposed substrate.
[0044] FIG. 31: Process steps for selective area single crystal
thin film semiconductor and sacrificial layer epitaxy on parent
substrate.
[0045] FIG. 32: Process steps for wafer bonding selective area
single crystal thin film regions on parent substrate with
alternative substrate.
[0046] FIG. 33: Process steps showing selective area thin film
semiconductor on alternative substrate layer separation via action
of release through removal of sacrificial layer.
[0047] FIG. 34: Schematic description of selective area thin film
semiconductor on alternative substrate and fabricated electronic
and or optoelectronic devices formed from thin film semiconductor
regions.
[0048] FIG. 35: Process steps for further deposition of thin film
semiconductor(s) upon patterned thin film single crystal
semiconductor on alternative substrate.
[0049] FIG. 36: Two junction solar cell formed from crystalline and
amorphous semiconductor devices disposed upon alternative
substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0050] An embodiment of the present invention is the manufacture of
thin film semiconductor-on-glass suitable for high performance thin
film transistors and solar energy conversion devices. It is
understood the present invention is applicable to other substrate
compositions other than glass, such as polymers, metals, ceramics,
and biologically active substrates and the like.
[0051] Furthermore, the present invention discloses alternate
embodiments of thin film semiconductors chosen from at least one of
silicon (Si), germanium (Ge), silicon-carbide (SiC.sub.x),
germanium carbide (GeC.sub.x), germanium nitride (GeN.sub.x),
silicon nitride (SiN.sub.x) tin germanium (SnGe.sub.x), tin oxide
(SnO.sub.x), gallium phosphide (GaP), gallium nitride (GaNx),
indium nitride (InNx), aluminium nitride (AlNx), zinc oxide
(ZnO.sub.x), magnesium oxide (MgO.sub.x) or combinations and
non-stoichiometric combinations thereof wherein x varies from >0
to .ltoreq.20 in some embodiments.
[0052] For example, GaN-based and ZnO-based compositions are
advantageous for light emitting diode applications disposed upon
glass substrates. Compositions such as (i)
Si.sub.xSn.sub.yGe.sub.zC.sub.w; (ii)
In.sub.xGa.sub.yAl.sub.zN.sub.w; and (iii)
Zn.sub.xMg.sub.yO.sub.zN.sub.w are also disclosed by the present
SoG invention wherein w, x, y, z vary from 0 to .ltoreq.1 in some
embodiments.
[0053] Alternative embodiments use Si, Ge and SiGe thin film
semiconductor compositions for SoG article manufacture of TFT and
solar cell devices disposed upon cheap glass and/or ceramic
substrates.
[0054] A general formula for oxide glass, but not limiting, may be
written for convenience as A.sub.nB.sub.mO.sub.z, where B represent
the network forming cation(s), A the modifying cation(s), O is
oxygen, and the real positive numbers m, n, z represent relative
chemical ratios varying from 0 to .ltoreq.1; it is understood that
additional impurities are present. If the A ions are introduced
into silica where B=Si, in the form of an oxide for example
A.sub.kO.sub.y; then
A.sub.nSiO.sub.z=(A.sub.kO.sub.y).sub.x.(SiO.sub.2).sub.1-x. For
example, the structure modifying A cations may act so as to plug
holes in the network formed by the B.sub.mO.sub.z. For example,
alkali silicate glass (A.sub.nSi.sub.mO.sub.z), use relatively
large cations of low charge e.g., A chosen from at least one of the
set {Na.sup.+, K.sup.+, Li.sup.+, Ca.sup.2+, Ba.sup.2+, Pb.sup.2+,
and the like}.
[0055] The silicate glasses are the most technologically and
commercially applicable material for the present invention, namely,
low cost and high volume manufacture thin film
semiconductor-on-glass for use in solar energy conversion and
display devices. The soda-lime-silica glass (SLSG), boro-silicate
glass (BSG) and boro-phosphate-silicate glass (BPSG) are exemplary
compositions for application to the present invention. It is also
understood, other compositions are equally covered by the present
invention, for example, alumino-silicate glass (ASG),
alkaline-earth silicate (AESG) glass and fluorine and/or chloride
containing silicate glasses.
[0056] High purity quartz substrates are composed of pure
SiO.sub.2, but are expensive compared to silicate glass substrates
which are typically composed of only a majority of silica,
SiO.sub.2,30-75%. Herein defined as SiO.sub.2-based glass.
Therefore, SoG devices fabricated on pure quartz substrates will
not typically suffer thin film contamination due to the substrate;
however a barrier layer as used herein may serve as a buffer layer
on quartz as a means to transition to a single crystal active
structure. Cost effective technical glasses useful for manufacture
of flat panel displays, TFTs, solar cells, light emitting devices
and the like, typically contain additional compounds, such as,
calcium oxide (CaO), sodium oxide (Na.sub.2O), potassium oxide
(K.sub.2O), aluminum oxide (Al.sub.2O.sub.3), boron oxide
(B.sub.2O.sub.3), zirconium oxide (ZrO.sub.2), zircon
(ZrSiO.sub.4), fluorine, lithium, lead oxide (PbO), alkaline earth
metal oxides (AEOx), transition-metal oxides (e.g., TiO.sub.2) and
others to a lesser extent.
[0057] Alkali ionic conduction in glass, and in particular silicate
glasses is a well studied process. Multi-component alkali silicate
glasses have historically been developed primarily for improving
glass formation properties suitable for various manufacturing
tolerances, increasing mechanical and/or optical performance. For
example, the addition of CaO into silicate glass introduces
Ca.sup.2+ ions forming relatively stronger Ca--O bonds compared to
Na--O bonds. The Ca.sup.2+ ions are held more firmly in the
structure and believed to improve chemical durability of a glass.
Addition of larger cations, via introducing CaO and MgO into the
Na.sub.2O.SiO.sub.2 glass increases stability of glass and allows
it to be made with a lower SiO.sub.2 content and improve glass
forming temperature and region and devitrification properties.
Regardless of the multi-alkali glass, it is generally found that
the dominant species responsible for ionic conduction is due to
sodium ions. The consequence of ionic conduction in silicate
glasses is becoming particularly problematic in SoG device
manufacture, where the finite conductivity and variation of
properties of thin films occurs when in contact with a silicate
glass.
[0058] In microelectronic and/or silicon integrated circuit
manufacture it is well established the presence of mobile
contaminants in group IV semiconductor (e.g.; Si) and dielectric
processing (e.g.; SiO.sub.2), particularly the presence of sodium
ions (Na.sup.+) and potassium ions (K.sup.+) ions are extremely
detrimental to device performance and yield. Borosilicate glasses
are not used in Si semiconductor processing due to not-intentional
boron doping effects. Sodium is extremely mobile in silica and
thermally grown SiO.sub.2 on Si and within low dielectric
interconnect layers. The presence of alkali ions, such as Na.sup.+,
in gate oxide and near SiO.sub.2/Si interfaces of Si-based
metal-oxide-semiconductor field effect transistors (MOSFETs) cause
electronic defects, traps, flat band voltage shifts, and
reliability and instability issues at high operating temperatures
and/or processing temperatures. Positive ions (e.g.; alkali ions
such as Na.sup.+, K.sup.+ and Li.sup.+ or alkaline earth ions, such
as Mg.sup.2+, Ca.sup.2+, Ba.sup.2+, Sr.sup.2+) can move relatively
freely within glass and/or SiO.sub.2 dielectric in response to an
applied electric field and/or thermal gradient, thereby forming a
source of mobile ionic charge. Significant effort is made to remove
sources of sodium and/or alkali contamination judiciously from Si
semiconductor processing. The remaining and persistent alkali
contamination within upper level interconnect layers is mitigated
in part via the use of phosphate glass (e.g.; P.sub.2O.sub.5),
phosphorous silicate glass (e.g.; P.sub.2O.sub.5.SiO.sub.2) and
silicon nitride compositions.
[0059] The presence of alkali ions disadvantageously affects
performance of metal-insulator-semiconductor (MIS) devices, such as
solar MIS solar cells and TFTs based on semiconductor-dielectric
MOSFETs. It is one object of the present invention to use alkali
barrier layer(s) in MIS solar cells fabricated from a SoG
article.
[0060] A solution to sodium permeability in glass compositions, in
particular, quartz and silica, has been disclosed in U.S. Pat. No.
5,631,522. The intentional doping of the low sodium containing
glass with aluminum (Al), yttrium (Y), cesium (Cs) and mixtures
thereof, has been shown to dramatically reduce sodium diffusion
through the doped glass used in sodium containing metal halide
lamps. It is disclosed herein that triply ionized rare-earth metal
ions, such as lanthanum (La) and erbium (Er), typically in the form
of rare-earth sesquioxides oxides, can be added to a Si lattice of
Cs or Y doped SiO.sub.2 glass to further minimize the sodium
diffusivity. The instant invention discloses the permeability of
sodium in glass can be lowered by advantageous doping of the
SiO.sub.2 glass by the addition of at least one of Al, Cs, La, Dy,
and/or Er and/or other rare earth metals, oxides, nitrides,
phosphides and/or combinations thereof.
[0061] Economical alkali-silicate glasses are composed of the very
impurities that are detrimental to TFT and solar cell performance.
Therefore, it is desirable for a simple and cost effective method
to be implemented in order to contain the impurities within the
glass substrate, such as mobile alkali ions, so as not to degrade
the performance of electronic devices based on thin film
semiconductors disposed upon the said glass substrate.
[0062] The present invention discloses and claims the use of at
least one alkali impurity barrier layer for SoG article manufacture
wherein the barrier layer is disposed between semiconductor thin
film(s) and a glass substrate.
[0063] The present invention claims the use of barrier layers, as
described above, for all SoG manufacturing techniques used to form
single crystal, polycrystal and/or amorphous thin film
semiconductors. For example, SoG article manufactures using: (i)
single crystal semiconductor thin film transferred via wafer
bonding; or (ii) direct epitaxy of amorphous semiconductor; or
(iii) direct epitaxy of amorphous-semiconductor and subsequent
recrystallisation; or (iv) direct epitaxy of polycrystalline
semiconductor; (v) direct epitaxy of single crystalline
semiconductor on a rare-earth based buffer layer(s).
[0064] The present invention discloses and claims the preferential
use of barrier materials for SoG manufacture using rare-earth
sesquioxide (RE.sub.2O.sub.3), rare-earth dioxide (REO.sub.2),
rare-earth monoxide (REO), rare-earth nitride (REN), rare-earth
oxynitride (REO.sub.xN.sub.y), rare-earth phosphide (REP),
rare-earth oxyphosphide (REO.sub.xP.sub.y), rare-earth carbide
(REC.sub.y), rare-earth oxycarbide (REO.sub.xC.sub.y), aluminum
rare-earth oxide (RE.sub.xAl.sub.yO.sub.w), and rare-earth
aluminosilicate (RE.sub.xAl.sub.ySi.sub.zO.sub.w), aluminum oxide
(Al.sub.2O.sub.3), silicon nitride (SiN.sub.x),
(Si.sub.xAl.sub.yN.sub.z) and combinations and non-stoichiometric
combinations thereof. A barrier material may comprise one or more
layers; wherein at least one layer comprises at least one compound
chosen from a group comprising a rare-earth sesquioxide
(RE.sub.2O.sub.3), rare-earth dioxide (REO.sub.2), rare-earth
monoxide (REO), rare-earth nitride (REN), rare-earth oxynitride
(REO.sub.xN.sub.y), rare-earth phosphide (REP), rare-earth
oxyphosphide (REO.sub.xP.sub.y), rare-earth carbide (REC.sub.y),
rare-earth oxycarbide (REO.sub.xC.sub.y), aluminum rare-earth oxide
(RE.sub.xAl.sub.yO.sub.w), and rare-earth aluminosilicate
(RE.sub.xAl.sub.ySi.sub.zO.sub.w), aluminum oxide
(Al.sub.2O.sub.3), silicon nitride (SiN.sub.x),
(Si.sub.xAl.sub.yN.sub.z) and combinations and non-stoichiometric
combinations thereof; wherein 0.ltoreq.w, x, y, z.ltoreq.1 as
required to make a predetermined compound of suitable
functionality.
[0065] A barrier material may comprise one or more layers; wherein
at least one layer comprises at least one compound chosen from a
group comprising
[RE].sub.x[RE].sub.y[RE].sub.z[C].sub.m[O].sub.n[N].sub.p[P].sub.r[Si].su-
b.s[Ge].sub.t[Al].sub.u wherein x>0 and at least one of y, z, m,
n, p, r, s, t, or u are >0. A barrier material may be single
crystalline; optionally it may be polycrystalline; optionally it
may be amorphous; optionally barrier material may comprise one or
more layers, at least one of which is single crystal.
[0066] The invention discloses the steps of:
a. preparing a clean glass substrate surface, b. depositing barrier
layer(s) upon a glass surface, chosen from compositions of at least
one of a rare-earth sesquioxide (RE.sub.2O.sub.3), rare-earth
dioxide (REO.sub.2), rare-earth monoxide (REO), rare-earth nitride
(REN), rare-earth oxynitride (REO.sub.xN.sub.y), rare-earth
phosphide (REP), rare-earth oxyphosphide (REO.sub.xP.sub.y),
rare-earth carbide (REC.sub.y), rare-earth oxycarbide
(REO.sub.xC.sub.y), aluminium rare-earth oxide
(RE.sub.xAl.sub.yO.sub.w), and rare-earth aluminosilicate
(RE.sub.xAl.sub.ySi.sub.zO.sub.w), aluminum oxide
(Al.sub.2O.sub.3), silicon nitride (SiN.sub.x),
(Si.sub.xAl.sub.yN.sub.z) and combinations thereof, c. forming a
thin film semiconductor layer on the barrier layer/glass substrate
composite article with the barrier layer disposed between the thin
film and the glass substrate.
[0067] The described SoG article can be formed using layer transfer
and/or direct wafer bonding and/or direct deposition and/or
recrystallization. The SoG article may comprise semiconductor
and/or barrier layers chosen from substantially single crystal
and/or polycrystalline and/or microcrystalline and/or
nanocrystalline and/or amorphous thin film crystal structure. I
rare-earth barrier layer may be deposited on a semiconductor prior
to attachment to a glass substrate.
[0068] Specifically, for solar cell operation it is desirable the
glass substrate function as the environmental barrier for the thin
film semiconductor and also as an optically transmissive coating
for low loss solar spectrum absorption into the said semiconductor.
Therefore, it is desirable for a barrier layer to exhibit optical
transparency to solar radiation. That is, a barrier layer is chosen
to exhibit a large band gap in excess of about 3 eV. In preference,
barrier layer compositions of rare-earth sesquioxide
(RE.sub.2O.sub.3), rare-earth dioxide (REO.sub.2), rare-earth
monoxide (REO), rare-earth oxynitride (REO.sub.xN.sub.y),
rare-earth oxyphosphide (REO.sub.xP.sub.y), rare-earth oxycarbide
(REO.sub.xC.sub.y), aluminum rare-earth oxide
(RE.sub.xAl.sub.yO.sub.w), and rare-earth aluminosilicate
(RE.sub.xAl.sub.ySi.sub.zO.sub.w), aluminum oxide
(Al.sub.2O.sub.3), silicon nitride (SiN.sub.x),
(Si.sub.xAl.sub.yN.sub.z) and combinations thereof.
[0069] A rare-earth metal can be chosen from at least one of
{.sup.57La, .sup.58Ce, .sup.59Pr, .sup.60Nd, .sup.61Pm, .sup.62Sm,
.sup.63Eu, .sup.64Gd, .sup.65Tb, .sup.66Dy, .sup.67Ho, .sup.68Er,
.sup.69Tm, .sup.70Yb and .sup.71Lu}, also known as the lanthanide
series. For purposes of the instant invention, yttrium, .sup.39Y,
is considered a rare-earth metal and considered included when [RE]
is used. Furthermore, it is also disclosed rare-earth oxide based
compounds containing Ge can also be utilized, such as, rare-earth
alumino-germanate, (RE.sub.xAl.sub.yGe.sub.zO.sub.w).
[0070] Furthermore, optionally, a barrier layer is chosen to
function as an insulator and/or dielectric. For thin film solar
cell and TFT using SoG, the insulating nature of a substrate is
advantageous for electrical isolation of devices on the SoG
substrate. Therefore, the function of the barrier layer and/or a
substrate may function as insulators and/or dielectrics,
alternatively or simultaneously. An added advantage of using
rare-earth oxide barrier layer in silicon-on-glass is the selective
silicon etch stop provided by the different chemistry of a
rare-earth compound versus a glass substrate. Another example solar
cell alternate embodiment is the use of barrier layer in SoG
article with properties of: (i) transparent to a substantial
portion of the solar spectrum with high energy absorption edge
greater than or equal to 3 eV; (ii) electrically conductive; and
(iii) provide resistance to transport of alkali ions. The barrier
layer with the aforementioned properties may act as an optically
transparent and electrically conducting layer and provide barrier
to alkali transport across said barrier layer. This buried
transparent conductive barrier layer (TCBL) can be used to form a
contact layer for vertical p-i-n and/or p-n junction solar cells
formed on the SoG article.
[0071] The drift of alkali ions through SiO.sub.2 in a MIS (where
M=Al, I=SiO.sub.2 and S=Si) structure is asymmetrical, where the
activation energy for drift from the metal-SiO.sub.2 interface is
larger than that from the Si--SiO.sub.2 interface. Traps at the
metal-SiO.sub.2 interface exhibit a deeper energy compared to the
Si--SiO.sub.2 interface, thereby making emission more difficult at
the former. The asymmetry is not present in poly-Si gate contact
MOS devices. The motion of sodium ions in particular, are governed
by emission of ions from traps at the interface and subsequent
drift through the oxide. The mobility of alkali metals is given by
the expression .mu.=.mu..sub.oexp(-E.sub.A/kT). Typical parameters
for Sodium: .mu..sub.o(Na.sup.+)=3.5.times.10.sup.-4 cm.sup.2/V.s,
E.sub.A(Na.sup.+).about.0.44; Potassium:
.mu..sub.o(K.sup.+)=2.5.times.10.sup.-4 cm.sup.2/V.s,
E.sub.A(K.sup.+).about.1.04; and Lithium:
.mu..sub.o(Li.sup.+)=4.5.times.10.sup.-3 cm.sup.2/V.s,
E.sub.A(Na.sup.+).about.0.47. In comparison, Copper exhibits
.mu..sub.o(Cu.sup.2+)=4.8.times.10.sup.-7 cm.sup.2/V.s,
E.sub.A(Cu.sup.2+).about.0.93.
[0072] FIG. 1A depicts schematically the physical MOS layer
structure formed on a SoG substrate comprising a thin film
semiconductor 102 in intimate contact with a high sodium ion
concentration glass substrate 101, such as
(Na.sub.2O).sub.x(SiO.sub.2).sub.y glass. A further dielectric
oxide 103 and polycrystalline semiconductor gate contact 104
followed by a metal gate electrode 105 form a general gate
stack.
[0073] FIG. 1B depicts the energy band structure of the MOS SoG
device as a function of cross-sectional distance vertically through
the layers. The high concentration of sodium ions 106 within the
glass substrate 101 are free to migrate 109 across interfacial
boundaries into the semiconductor thin film 102, oxide layer 103
and polycrystalline semiconductor layer 104. For the present
example in FIG. 1B, the band energy alignments are shown for thin
film semiconductor chosen from single crystal Si, the oxide
103=SiO.sub.2, layer 104=poly-Silicon and metal contact 105
M=Aluminum. If the MOS SoG structure is illuminated by 3.5-5 eV
ultraviolet photons, electrons from the conduction (107) and
valence (108) band of Si may be injected into the SiO.sub.2
conduction band (CB). These UV generated and injected electrons may
be capable of passivating and/or neutralizing the Na.sup.+ ions
residing at the metal-SiO.sub.2 and Si--SiO.sub.2 interfaces.
Nevertheless, it is disclosed the large concentration of alkali
ions sourced from the glass substrate deleteriously degrade the
performance, long term stability and reliability of the MOS SoG
device. Possible prior art solutions are: (i) the use of
multi-alkali effect in alkali silicate glasses, which can be used
to significantly reduce ionic conductivity; or (ii)
Alumino-borosilicate glasses, which may act as sinks for sodium and
other process impurities.
[0074] The present invention discloses a solution to the problem of
alkali contamination of the thin film semiconductor active layer
via the use of barrier layer as is shown in the modified MOS SoG
structure of FIG. 2. The alkali-silicate glass 101 of FIG. 2A
depicts sodium ions 106 blocked from migrating beyond the alkali
barrier layer 200. The barrier layer 200 is disposed substantially
between the thin film semiconductor layer 102 and the glass
substrate 101. Silicon dioxide has a band gap energy of
E.sub.g(SiO.sub.2).about.8.8 eV and the barrier layer 200 has a
band gap of E.sub.BL<E.sub.g(SiO.sub.2). FIG. 2B, shows a
further criteria for the alkali barrier layer which is the
advantageous partitioning of the valence (.DELTA.E.sub.v) and
conduction (.DELTA.E.sub.c) band offsets relative to the thin film
semiconductor conduction band (CB) and valence band (VB)
extrema.
[0075] A simple yet instructive model of a two component
sodium-silicate glass (Na.sub.2O).(SiO.sub.2)=Na.sub.2SiO.sub.3 is
now described to aid but not limit the utility of engineering
sodium-ion barrier layer(s) in SoG article. For example, the range
of glass formation in the Na.sub.2O--SiO.sub.2 system is continuous
from SiO.sub.2 up to the meta-silicate composition
Na.sub.2SiO.sub.3, which does not readily form a glass phase.
Silica is a continuous network of SiO.sub.4 tetrahedra. The
introduction of Na.sub.2O into SiO.sub.2 results in the formation
of singly-bonded or non-bridging oxygen atoms, where the oxygen
atoms are linked to only one Si atom. That is, not all oxygen atoms
are bonded to two silicon atoms as in the SiO.sub.4 network. Sodium
ions are linked to surrounding oxygen atoms via ionic bonds that
are much weaker than Si--O bonds. The extra oxygen atoms supplied
by the Na.sub.2O increases the oxygen-to-silicon ratio O:Si>2.
Therefore, sodium silicate glass is structurally weaker than pure
vitreous silica (SiO.sub.2). Increasing the Na.sub.2O content
causes a greater number of non-bridging oxygens to be formed, until
the material phase segregates into isolated SiO.sub.4 tetrahedra
linked together by ionic Na--O bonds.
[0076] By way of example and not intended to be limited to any
particular theory, is the use of rare-earth compounds, such as
rare-earth oxides (REOx), as barrier layer. REOx compositions
exhibit approximately, eqi-partition conduction band offset
.DELTA.E.sub.c.about.2.4 eV relative to single crystal Si. Binary
rare-earth oxides with the pyrochlore and bixbyite crystal
structures are vacancy-ordered derivatives of the CaF.sub.2-type
fluorite structure and exhibit lattice parameters approximately
twice that of Si. Therefore, a close lattice match with Si and
other elemental and/or compound semiconductors can be achieved by
combinations of various rare-earth compounds such as metal oxides.
Defects, such as misfit dislocations, at the Si/rare-earth oxide
dielectric interface influence the mobility of charge carriers in
the underlying semiconductor layer. Extended defects in
bixbyite/Silicon epitaxy such as REOx films grown on Si(111) and
Si(001) may also be used advantageously in the present invention
for electrical conductivity optimization. The REOx bixbyite
structure can be described as a vacancy ordered fluorite with two
oxygen vacancies per fluorite unit cell, causing the bixbyite unit
cell parameter to be twice that of fluorite in all three
dimensions. Atomic and molecular interstitial defects and oxygen
vacancies in single crystal rare-earth oxide (REOx) can also be
advantageously engineered via non-stoichiometric growth conditions.
The atomic structure of singly and doubly positively charged oxygen
vacancies (O.sub.v.sup.+, O.sub.v.sup.2+), and singly and doubly
negatively charged interstitial oxygen atoms (O.sub.i.sup.-,
O.sub.i.sup.2-) and molecules (O.sub.2i.sup.-, O.sub.2i.sup.2-) can
be engineered in defective single crystals of REO.sub.x=1.5.+-.y,
0.ltoreq.y.ltoreq.1). Rare-earth metal ion vacancies and
substitutional species may also occur and an oxygen vacancy paired
with substitutional rare-earth atom may also occur. However, atomic
oxygen incorporation is generally energetically favored over
molecular incorporation, with charged defect species being more
stable than neutral species when electrons are available from the
rare-earth conduction band. It is disclosed that oxygen vacancies
advantageously inhibit alkali ion transport and thus can be used as
a component of an effective barrier layer. It is disclosed in the
present invention that oxygen vacancies can be used as part of a
rare-earth based compound as an effective barrier to positive ion
migration, and more preferably inhibit Na.sup.+ ions.
[0077] Optional barrier layer materials are, for example,
rare-earth nitride (REN), rare-earth oxynitride (REO.sub.xN.sub.y),
rare-earth phosphide (REP), rare-earth oxyphosphide
(REO.sub.xP.sub.y), rare-earth carbide (REC.sub.y), rare-earth
oxycarbide (REO.sub.xC.sub.y), aluminium rare-earth oxide
(RE.sub.xAl.sub.yO.sub.w), and rare-earth aluminosilicate
(RE.sub.xAl.sub.ySi.sub.zO.sub.w), aluminium oxide
(Al.sub.2O.sub.3), silicon nitride (SiN.sub.x),
silicon-aluminium-nitride (Si.sub.xAl.sub.yN.sub.z), phosphate
glass, P.sub.5O.sub.5, borophosphate silicate glass BPSG, and
combinations and non-stoichiometric combinations thereof.
[0078] Chlorine may also be used to inhibit sodium ion transport in
silica. Therefore, a chlorinated surface of silicate glass is also
a possible alkali diffusion barrier; optionally a barrier layer
high in free chlorine in combination with a rare-earth composition
is disclosed.
[0079] FIG. 3 describes the geometry used for ion implantation of
foreign species 301 into preferentially CZ Si substrate 304 to form
a Gaussian profile distribution volume 302 of said ions in the Si
crystal. The defect plane 303 substantially plane parallel to the
Si crystal surface. The depth of the peak of the defect layer
distribution residing a distance L.sub.D from the Si surface. An
optional protective oxide layer and/or alkali barrier layer, 306 is
also shown.
[0080] FIG. 4 shows calculated depth profiles for H+ ions 401 using
various incident energy implants. In preference the ion species is
chosen from hydrogen and/or helium. For the case of Fr, the peak
depth L.sub.D versus implant energy range 100 keV.ltoreq.E.ltoreq.5
MeV is shown. Clearly, the defect layer depth beneath the surface
can be placed in the range 1.ltoreq.L.sub.D<250 .mu.m, depending
on the energy used. The calculated results were performed using
SRIM 2003 ion implant code, and L.sub.ox=200 .ANG. SiO.sub.2. FIG.
5 shows exemplary ion implantation into an original device
substrate. FIG. 6 shows exemplary ion implantation into an original
device substrate.
[0081] FIG. 7 shows the distribution of Fr ions 701 in the buried
layer beneath the Si surface for the case of 3 MeV.
[0082] In one embodiment a process is used to fabricate a vertical
type opto-electronic solar spectrum energy conversion device using
thin film single crystal semiconductor layer transfer method. In
preference the semiconductor is chosen from silicon or germanium or
combinations thereof, an alternative substrate is chosen from
silicate glass compositions, and more preferably alkali-silicate
glasses. The alkali barrier layer is chosen according to the
specifications disclosed in the present invention.
[0083] FIG. 8 shows individual parallel process paths for
fabrication of thin film single crystal solar cell on glass
article. A single crystal CZ Si substrate 801 and alternative
substrate 807 are cleaned and prepared for processing. An optional
SiO.sub.2 protective layer 802 is deposited or thermally grown on
the CZ Si substrate 801. A barrier layer may also be deposited upon
or in place of layer 802. The CZ substrate is then implanted
according to the method described in the present invention to form
a buried defect layer 804. A cleaned alternative substrate 807 is
then deposited with a uniform barrier layer 808.
[0084] Alternative substrate 807 is preferably chosen from
alkali-silicate glass. FIG. 9 shows how the alternative substrate
with insulating and/or conductive barrier layer 809 and implanted
CZ Si substrate 806 are joined together 810 with opposing surfaces
850 and 860. The surfaces must be free from particulate
contamination and can be vacuum joined, van der Waals or anodic and
the like bonded together. FIG. 10 shows how a compound multilayer
article 811 is then subjected to thermal annealing sequence 813 to
strengthen the bond between surfaces 850 and 860 and to initiate
temperature dependent defect fracture 814 confined to a region
advantageously aligned with CZ Si crystallographic axes. A thermal
anneal sequence 813 generates fracture within said CZ Si crystal
confined substantially to the plane defined by the defect
plane.
[0085] FIG. 11 next shows how, with application of external
mechanical stimulus 815 to at least one region of the edge of the
compound article 811, the fracture propagates throughout the defect
plane causing physical separation of remaining bulk CZ Si substrate
816 and thin film CZ Si coupled to alternative substrate 817. The
resulting defect plane may exhibit rough surface 818 on both the
exposed thin film CZ Si and the cleaved surface of the bulk
substrate. The surface roughness of 818 may have surface features
ranging from several nanometers to several micrometers depending on
the 0:H ratio and implant energy. Typically, higher implant
energies result in wider full width at half maximum of the Gaussian
defect layer. For example, a 3 MeV Fr implant results in a straddle
of .about.1 .mu.m.
[0086] FIG. 12 shows how the wafer bonded thin film CZ Si and thus
formed buried barrier layer on the glass substrate 817 are then
processed to form a vertical type MIS, p-n junction and/or p-i-n
diode solar cell device 832. The vertical solar cell functions by
converting incident solar radiation coupled into the thin film
semiconductor layers 833 into photo-generated electronic charge
carriers. The incident solar radiation is directed in a vector
initially incident upon the glass substrate surface, through the
glass substrate and into the thin film absorber region. Example
solar cell devices are disclosed in the next section. Further, thin
film semiconductor and/or dielectric and/or metallic layers may be
directly deposited upon surface 818 of SoG article 817. Thin film
single crystal semiconductor layer 819 is suitable for direct
epitaxy of further single crystal semiconductors and dielectrics.
For example, the initial bulk Si substrate 801 may be chosen as
p-type Si (p:Si). The completed SoG article is therefore a single
crystal p:Si thin film on glass article. A p-i-n diode structure
can be formed from the p:Si SoG by further deposition of
not-intentionally-doped intrinsic Si layer 830, followed by a
n-doped Si layer 831. The p-i-n Si homojunction diode 833 is
suitable for solar cell devices.
[0087] FIG. 13 discloses an example method and general process flow
for fabricating multiple single crystalline semiconductor layers
1312 upon a bulk single crystal semiconductor substrate 1301. The
multi-layer semiconductor stack 1312 is separated by
ion-implantation technique 1306 as described previously by a defect
layer 1308.
[0088] Implanted ion species are chosen in preference from H.sup.+
and/or He.sup.+ ions. FIGS. 5 and 6 show exemplary ion implantation
into an original device substrate. Alternatively, methods disclosed
in U.S. application Ser. No. 11/788,153 are incorporated herein in
their entirety by reference; the instant invention discloses the
addition of a rare-earth based barrier layer in combination with
previously disclosed semiconductor and/or solar cell
structures.
[0089] An example layer sequence 1312 is composed of: p-type Si
substrate 1301; intrinsic Si (1302); n-type Si 1303; intrinsic Si
1304; p-type Si 1305. Upon wafer bonding onto glass substrate 809,
as shown in FIG. 14, a remaining portion of thin film Si 1311 is
separated from the bulk of the Si substrate 1301 via defect layer
1308.
[0090] FIG. 15 shows the transferred layer stack 1312 forming a
p-i-n-i-p doped Si multilayer diode coupled to the glass substrate
809. The structure multilayer single crystal Si SoG device 1520 is
suitable for solar cell operation by coupling solar radiation 1530
through the transparent substrate 807 and barrier layer 808 into
the active region(s) comprising 1312. The final surface 1510
defined by the defect plane can be metallized to form an optical
reflector and/or electrical contact(s).
[0091] FIG. 16A shows a general solar power spectrum 1601,
punctuated with multiple absorption regions. The peak spectral
variance 1606 occurs at .lamda..about.496 nm (.about.2.5 eV) in the
400<.lamda..ltoreq.600 nm region. Prior art optical
photon-to-electron conversion devices employing semiconductors are
well known. FIG. 16A shows the absorption coefficient
.alpha..sub.abs 1604 of single crystal silicon (Si) 1603 and
germanium (Ge) 1602 semiconductors. The indirect bandgap
semiconductors Si and Ge span major portions of the solar spectrum.
Close to the energy band gap, both Si and Ge have long wavelength
absorption tails due to the indirect energy-momentum band
structure. Looking closely at the absorption coefficient of Si in
FIG. 16A, it is shown that the absorption depth near the fundament
band gap energy (E.sub.g(Si)=1.1 eV) is extremely long. This means
that photons with energy equal to or slightly greater than band gap
energy E.sub.g(Si).gtoreq.1.1 eV will penetrate a depth
L.sub.e=1/.alpha..sub.abs, deep within the crystal. That is, for
900<.lamda.<1120 nm the penetration depth for 1/e absorption
(L.sub.1/e) is 10<L.sub.1/e<1000 .mu.m, thus requiring thick
Si substrates for bulk band edge solar cells. Not well known by
researchers in the field, is the fact, that Si possesses one of the
highest known absorption coefficient for all commercially mature
semiconductors in the blue to UV region, .lamda..about.<450
nm.
[0092] FIG. 16A also shows the overlap of Ge 1602 absorption with
the solar spectrum 1601 as a function of wavelength 1605. Ge
exhibits 10-100.times. higher absorption co-efficient than Si in
the 1.1-3 eV range. This means 10-100.times. thinner film absorbers
using Ge are possible compared to Si. The use of Ge extends
absorption down to 0.66 eV and therefore can potentially access
more of the available solar spectrum and available power. For the
case of high volume, large area and low cost solar cell
fabrication, large Si substrates (.phi..sub.max=450 mm diam., CZ
growth) are still advantageous and at least .about.10-50.times.
cheaper than Ge substrates (.phi..sub.max=150 mm, CZ growth).
[0093] It is an aspect of the present invention to fully utilize
the unique optical and electronic properties of single crystal Si
to form new types of high efficiency solar cell devices.
Furthermore, the utility and cost structure of wafer bonding is
severely limited in available single crystal bulk substrate
diameters if anything other than Si is used.
[0094] In theory, Si should be a very efficient solar cell
material; however high energy photons degrade the conversion
efficiency. FIG. 16B shows the energy band structure of bulk single
crystal Si as a function of energy 1650 and wave-vector 1651. The
periodic array and definite symmetry of Si atoms in the crystal
forms an extended band structure consisting of conduction (CB) 1652
and valence (VB) 1653 bands. Electrons and holes are constrained to
satisfy the E-k dispersion, as shown. Silicon exhibits a complex
band structure due to the diamond-like crystal lattice, with
critical point energy gaps E.sub.G=1.1 eV, E.sub..GAMMA.1=3.4 eV,
E.sub..GAMMA.2=4.2 eV, E.sub.X=1.2 eV, E.sub.L=2.0 eV, E.sub.L=44
meV. The unstrained bulk valence band is composed of a heavy- (HH)
and light-hole (LH) band, degenerate at zone center k=0. The
fundamental and indirect band gap E.sub.G, requires phonon
participation for creating an electron-hole pair via absorption of
a photon with energy (E.sub..gamma.) co-incident with E.sub.G.
Referring to FIG. 16B, Si also possesses direct energy band gaps
between E.sub..GAMMA.1 and E.sub..GAMMA.2, resulting in very high
absorption co-efficients (refer short wavelength portion of FIG.
16A). High energy blue and UV photons are efficiently absorbed
(within 0.11 .mu.m of the surface for 400 nm photons, refer FIG.
16A) in the upper conduction and valence bands creating hot
electron hole pairs with large excess energy relative to the
fundamental edges at E.sub.G. These hot carriers couple to the
lattice and quickly thermalize or equilibrate by emitting lattice
phonons of energy .omega..sub.LO. The UV photogenerated carriers
therefore cannot easily participate in photocurrent generation in
bulk and/or thick Si p-n SJ devices relying on large carrier
transit distances. It is an object of the present invention to
design high energy photon absorption Si solar cell capable of
extracting the energetic photogenerated carriers.
[0095] In order to increase UV responsivity in Si, it is necessary
to avoid dead layer formation on the irradiated Si surface. A
method to circumvent dead layer region formation is via creating a
charge inversion layer at the interface between a dielectric
material and semiconductor, for example the SiO.sub.2/Si interface.
Alternatively, an inversion layer can be generated by a potential
energy Schottky barrier via appropriate work function metal placed
in contact with intrinsic Si. The UV response of the inversion
layer is superior to vertical and/or planar p-n and/or p-i-n
junction type photodiodes. Photovoltaic operation can be optimized
via a built-in voltage generated by advantageous placement of a
lightly doped junction formed close to the surface of the device.
High quality SiO.sub.2 has a large band gap Eg(SiO.sub.2).about.8.8
eV, and does not absorb high energy solar UV light. Depending on
the growth and/or deposition technique used to form SiO.sub.2, the
optical properties can be modified. Using gas source deposition,
various amounts of hydrogen may be incorporated in the amorphous
oxide layer. The hydrogen may affect the transmission/absorption
properties of the film. Conversely, SiO.sub.2 and hydrogen are
beneficial for surface passivation of the Si surface states which
is a desirable property.
[0096] Thermally grown SiO.sub.2 via oxidation and thus consumption
of Si produces the highest quality oxide and Si/SiO.sub.2
hetero-interface. The band alignment for the poly-Si gate contact
MOS device using the Si/SiO.sub.2 system is shown in FIG. 1B. The
energy difference between the Si CB and the SiO.sub.2 CB is
.DELTA.E.sub.c.about.3.1 eV. Similarly, the energy difference
between the Si VB and SiO.sub.2 CB is .about.4.2 eV. Higher energy
photons with energy in excess of 3.1-4.2 eV are therefore capable
of injecting electrons from Si into the oxide. This effect can be
used advantageously in devices disclosed herein.
[0097] Typically, SiO.sub.2 is an optimal antireflection (AR)
coating as well as a passivation layer. Transparent low loss AR
layers are used in the present invention. Typically, wide band gap
energy materials optically transparent to the solar spectrum, such
as, SiO.sub.2, Aluminium-oxide (Al.sub.2O.sub.3) magnesium-oxide
(MgO), calcium fluoride (CaF.sub.2), magnesium fluoride
(MgF.sub.2), silicon-nitride (Si.sub.3N.sub.4), titanium-dioxide
TiO.sub.2, tantalum-pentoxide (Ta.sub.2O.sub.5) and the like are
used. The present invention further teaches a new class of wide
band gap optical materials suitable for optical coating,
specifically, the materials of rare-earth metal oxide (REO.sub.x),
rare-earth metal oxynitride (REO.sub.xN.sub.y) and rare-earth metal
oxy-phosphide (REO.sub.xP.sub.y), and combinations thereof, glasses
and/or crystalline material. A rare-earth metal is chosen from the
group commonly known as the lanthanide series. Mixtures including
Si, Ge, C, combinations of rare-earths and/or silicates can also be
used with the aforementioned rare-earth based materials. An optical
coating may comprise one or more layers wherein at least one layer
comprises at least one compound chosen from a group comprising:
[RE].sub.x[RE].sub.y[RE].sub.z[C].sub.m[O].sub.n[N].sub.p[P].sub.r[Si].su-
b.s[Ge].sub.t[Al].sub.u wherein x>0 and at least one of y, z, m,
n, p, r, s, t, or u are >0. A coating layer may be single
crystalline; optionally it may be polycrystalline; optionally it
may be amorphous; optionally optical coating material may comprise
one or more layers, at least one of which is single crystal.
[0098] A metal-insulator-semiconductor (MIS) device fabricated upon
a glass substrate is disclosed in FIGS. 17A & 17B. The thin
film single crystal semiconductor layer 1703 is fabricated upon a
transparent substrate 1701 according to the methods of the present
invention. Layer 1703 with thickness 1711 is chosen from single
crystal Si, and the substrate 1701 with thickness 1713 is chosen
from low cost alkali-silicate glass. An alkali barrier layer 1702
with thickness 1714 separates the thin film semiconductor 1703 from
the glass substrate 1701 in order to prevent alkali ion
contamination.
[0099] The SoG substrate is fabricated into the MIS device via
optional selective oxidation of thin film Si layer 1703 into
SiO.sub.2 regions 1704 and/or 1705. Layer 1705 is a dielectric
and/or insulating material and can be chosen from SiO.sub.2,
SiN.sub.x or single crystal rare-earth oxide compositions as
disclosed in U.S. Pat. No. 7,199,015, titled "Rare-earth oxides,
nitrides, phosphides and ternary alloys with Silicon". The
insulating layer 1705 is preferably grown thin to act as a tunnel
barrier, although thick layers can also be used. The metal or
conductive contact layer 1706 collects photo-created carriers
generated in the active layer 1703 and in a region proximate to the
Si/insulator interface. Electrical contacts to the active layer
1707 complete the circuit. Incident optical radiation 1720 enters
the glass substrate and is absorbed in the thin film Si layer 1703.
Photons that are not absorbed on first pass through 1703 are
reflected by the oxide electrode 1706, thereby enabling a second
pass 1721 through the active layer 1703. This constitutes a 2-sun
solar cell device. The MIS SoG equivalent circuit is shown in FIG.
17B. Electrical contacts 1707 are equivalent. Metallization chosen
for contacts may be different for the purpose of low ohmic contact
1707 to 1703 and/or specific work function metal for the oxide
contact 1706. An optional AR coating 1730 can be deposited upon the
glass substrate 1701 to minimize reflection losses 1722. The AR
coating may consist of multiple layers composed of transparent and
different refractive index materials.
[0100] Another embodiment of a MIS SoG solar cell device is
disclosed in FIGS. 18A & 18B. The devices are fabricated in a
similar fashion to the description of FIG. 17A, however, multiple
lateral devices are shown interconnects via a common active layer
contact 1707. The MIS repeating unit is laterally disposed across
the SoG substrate on unit dimension 1810. The distance between the
electrodes 1707 & 1707 is shown as 1820. The electrode
dimensions and spacing are chosen to optimize the cell efficiency
and is dependent upon the materials used. It is disclosed the
active layer is continuously optically active and does not suffer
dead layers due to opaque electrodes impeding the coupling of
optical radiation into the active thin film 1703.
[0101] The multiple MIS SoG equivalent circuit is shown in FIG.
18B. Contacts 1707 can be grouped and connected together forming an
electrode suitable for the extraction of photocurrent. Similarly,
electrodes 1706 can also be connected together, thus forming
multiple parallel connected MIS SoG devices. That is, grouped
contacts 1706 and 1707 form an external two electrical terminal
module composed of parallel interconnected MIS devices.
Alternately, series connected devices can be fabricated via
suitable electrical isolation of the thin film semiconductor.
[0102] Another embodiment of the present invention is the use of
multilayer semiconductor structures disposed upon the glass
substrate. Another embodiment is the use of single crystal
semiconductor layers to form the active regions. Yet another
embodiment is the use of Si layers chosen from not-intentionally
doped (i.e., substantially intrinsic, i), n-type (n) and p-type (p)
doping. For solar energy conversion devices, layered Si devices of
the form of p-n and p-i-n diodes are efficient optoelectronic
conversion structures. An example p-i-n SoG embodiment is shown in
FIG. 19A. The fabrication of the p-i-n SoG structure is possible
using the methods disclosed in the present invention. It is
understood that p-n junctions and more complex structures are also
possible. The glass substrate 1701 is separated from the single
crystal thin film semiconductor 1902 layer via a barrier layer 1702
according to the methods disclosed.
[0103] The p-i-n layer structure is composed of p-type Si (p:Si)
1902, intrinsic Si (i:Si) layer 1903, and n-type Si (n:Si) layer
1904. Layers 1903 and/or 1904 can be deposited upon an initial SoG
article comprising n:Si on glass. Alternatively, the p-i-n
structure can be initially deposited upon the single crystal p:Si
substrate prior to wafer bonding and implant induced layer
separation. Lateral oxidation of layer 1902 may be used for lateral
electrical isolation of devices disposed across the SoG substrate
via regions 1901. Passivation and/or environmental sealing of the
Si epi-layers is via layer 1905 and may consist of SiO.sub.2 and
SiN.sub.x. Electrical contacts formed by 1906 to the n-type layer
1904 and 1908 to p-type layer 1908 may not be the same composition.
For, example, ohmic contacts to the different conductivity type
layers may require different metals. The active area useful for
photocurrent generation is defined by the i-layer width 1907 of
thickness 1923. Optical radiation is coupled in from the glass
substrate 1720 into the pin device. The contact 1906 defines a
reflective surface that enables regeneration of photons such that
another pass through the i-region may occur. This constitutes a
2-sun concentrator p-i-n solar cell fabricated in a SoG structure.
The equivalent circuit is shown in FIG. 19B, and is represented by
a p-i-n diode 1920.
[0104] Multiple lateral p-i-n devices can be fabricated across the
SoG substrate as shown in FIG. 20A. Utility of the highly resistive
glass substrate and/or barrier layer is for the purpose of
electrical isolation via lateral oxidation and/or etching.
[0105] Regions 1901 electrically isolate devices formed on layer
1902. The metallization (M) and/or electrical contacts 2010 shows
series interconnection of p-i-n device forming the string
p-i-n-M-p-i-n-M-p-i-n . . . . Optical radiation incident 1720 upon
the glass substrate 1701 is coupled through the transparent barrier
layer 1702 into the i:Si 1903 layers and reflected off the contacts
2010, thereby forming the 2-sun concentrator structure. Passivation
and/or environmental sealing of the p-i-n devices is via coating
2015. The equivalent circuit is shown in FIG. 20B where p-i-n
devices 1920 are series connected. Photocurrent generated within
each device flows through interconnects 2010 thereby forming two
terminal external module.
[0106] The absorption co-efficient as function of wavelength for
the thin film semiconductor layer can be used for selecting the
thickness and wavelength region operation. In particular, Si
exhibits a highly non-linear absorption character as a function of
optical wavelengths. Referring to FIG. 16A, it can be seen
.alpha..sub.abs(.lamda.) in Si varies by almost five orders of
magnitude in the range 350.ltoreq..lamda..ltoreq.1127 nm. Short
wavelength photons are therefore absorbed in a very short distance
compared to long wavelength photons in the vicinity of the indirect
band gap E.sub.G.
[0107] FIG. 22A discloses a stacked layer structure consisting of
two p-i-n diodes comprising different intrinsic absorber
thicknesses. In preference, the semiconductor is selected from
single crystal Si and the substrate from alkaline-silicate glass.
An example embodiment discloses a first p-i-n diode comprising p:Si
layer 2204, i:Si layer 2205 and n:Si layer 2206. A second p-i-n
diode formed upon the first diode comprising p:Si layer 2207, i:Si
layer 2208, and n:Si layer 2209. This sequence forms the
p-i-n-p-i-n stacked diode. Alternately, the sequence n-i-p-n-i-p
can also be formed. Yet another embodiment uses the layer sequences
p-i-n-i-p or n-i-p-i-n. Regardless, the NID i-regions are grown
with different thickness, L.sub.s 2301 and L.sub.L 2311, such that
the thinner region is positioned closest to the glass substrate.
The electrical contact layers 2211 and 2212 are formed on the first
and last layers comprising the stacked diodes. Incident short
wavelength optical radiation .lamda..sub.s enters the glass
substrate 2201 and is preferentially absorbed in the first thin
i:Si layer 2205 and/or p-i-n diode. Similarly, long wavelength
optical radiation .lamda..sub.L enters the glass substrate 2202 and
is preferentially absorbed in the second thick i:Si layer 2208
and/or p-i-n diode.
[0108] FIG. 22B shows the generation rate G(.lamda., z) 2225 of
electron-hole pairs as a function of vertical distance, z 2220,
through the layered structure.
[0109] Short wavelengths in Si exhibit very large absorption
co-efficient (100 .mu.m.sup.-1 @ .lamda..sub.s=400 nm) and thus the
first i:Si region 2205 can be made thin (L.sub.L.about.0.01 .mu.m).
Similarly, long wavelength photons co-incident with the band edge
E.sub.G exhibit relatively low absorption co-efficient and thus can
be made thick 0.01 .mu.m.sup.-1 @ .lamda..sub.s=1000 nm,
L.sub.L.about.100 .mu.m).
[0110] FIGS. 23A & 23B further show wavelength bands 2300 &
2310 used for, as an example, tandem Si: p-i-n-p-i-n solar cells.
The theoretical efficiency of the proposed tandem cell is
equivalent to a two-junction solar cell, and thus in excess of the
SJ limit=25%. It is important to note that the disclosed
two-junction device uses only Si semiconductor materials in the
layer stack. This technique works particular well for Si compared
to Ge due to the large non-linearity in absorption co-efficient of
Si as a function of wavelength and advantageous overlap with the
solar spectrum.
[0111] Another embodiment utilizes a hybrid device based on
incorporating the advantageous features of MIS and PIN solar cell
devices. FIG. 24 discloses a MIS/PIN hybrid wherein the MIS section
2420 is used as the short wavelength converter and the PIN device
2430 is used as the longer wavelength converter. In preference, the
semiconductors forming the stacked layers are single crystal and/or
polycrystalline and/or amorphous structure. The insulator 2402
layer may be chosen from amorphous SiO.sub.2 and/or single crystal
rare-earth based materials, such as rare-earth oxide and oxynitride
(REO.sub.x or REO.sub.xN.sub.y). If insulator 2402 is amorphous
then thin film semiconductor layer 2400 may be chosen from
polycrystalline and/or amorphous structures using the wafer bonding
technique disclosed herein. Alternately, multiple wafer bonding
steps may be used to form single crystal layers 2400, 2403, 2402
and 2405 prior to lamination with glass substrate 1701. If the
insulator 2402 is chosen from substantially single crystal
compositions (e.g.; rare-earth oxide and like), then epitaxial Si
may be deposited directly upon 1402, thereby forming a single
crystal epitaxial growth sequence according to the method disclosed
in the present invention.
[0112] Referring to FIG. 24, an example embodiment of the MIS/PIN
hybrid is via the following layer sequence: alkali silicate glass
substrate 1701; alkali barrier layer 1702; a first semiconductor
layer p:Si 2400; a insulator layer 2402; a n:Si layer 2403; a NID
i:Si layer 2404; and a p:Si layer 2405. Electrodes 2406 and 2407
may be metallization to contact layers 2405 and 2400, respectively.
The layer sequence forms a MIS diode with silicon contact layer to
the insulator. In fact, the p:Si/SiO.sub.2/n:Si stack (i.e.;
2400/2402/2403) forms an inversion channel MOS structure suitable
for high energy photon solar energy conversion. The following NIP
(n:Si/i:Si/p:Si) structure is formed via the layer sequence
2403/2404/2405. The intrinsic layer 2404 thickness is chosen to
advantageous absorb a portion of the solar spectrum that has not
been depleted by the MIS device.
[0113] Solar optical radiation is incident upon the glass substrate
1701 and is coupled into the MIS/PIN hybrid via an optional
transparent barrier layer 1702.
[0114] The MIS device is preferentially made with a thin insulator
1402 (5.ltoreq.L.sub.ox.ltoreq.500 Angstroms) so as to allow
tunneling of photo-created carriers in the active layer 2400.
Referring to FIG. 2B, the possibility UV generated hot electron
injection from the CB and/or VB of Si into the CB of the insulator
may also occur. Electrode 2406 can also be engineered to function
as a back reflector allowing long wavelength radiation not absorbed
by the MIS section to be recycled back through the device.
Therefore, the MIS/PIN hybrid solar cell fabricated on SoG also
form a two-junction and 2-sun solar concentrating device.
[0115] The present invention discloses a new manufacturing method
of forming thin film and single crystal semiconductor layer(s)
disposed upon glass substrates. Furthermore, a method using alkali
barrier layers is disclosed in order for low cost alkali-silicate
glass to be used. New solar cell structures on glass or other
inexpensive substrates are enabled by the disclosed methods. As
used herein, alternatives to glass substrates may be used wherever
glass has been given as an example; alternatives to glass include,
but are not limited to, plastics, including polyimide and Kapton,
flexible plastics, insulative coated metal, ceramic, recycled
silicon wafers, silicon ribbon, poly-silicon wafers or substrates
and other low cost substrates known to one knowledgeable in the
art.
[0116] Solar energy conversion devices disclosed using the thin
film semiconductor SoG article are: (i) single absorber MIS, PIN
devices; (ii) dual absorber PINIP, NIPIP, PINPIN, MIS/PIN hybrid. A
unique aspect of disclosed solar cell devices is the recycling of
photons that have not been absorbed in a first pass through the
device via a reflective back electrode. This constitutes a 2-sun
concentrator structure, enabling increased efficiency beyond the
single junction limit.
[0117] Yet another unique aspect of disclosed solar cell devices is
the preferential use of the non-linear absorption of silicon as a
function of wavelength in order to construct dual wavelength solar
cell. This constitutes a 2-junction device structure, enabling
increased efficiency beyond a single junction limit.
[0118] In one embodiment a device for converting radiation to
electrical energy comprises an active layer for the converting
radiation to electrical energy, a barrier layer and, optionally, a
replacement substrate, optionally with electrodes connecting to the
active layer, wherein the active layer, optionally, comprises one
or more different rare-earth ions and the barrier layer comprises
at least one rare earth and separates the active layer and the
replacement substrate.
[0119] In one embodiment a device for converting radiation to
electrical energy comprises an active layer for the converting
radiation to electrical energy; and a replacement substrate
transparent to a majority, at least 50%, of the radiation for
converting. A device for converting radiation to electrical energy
comprises, optionally, a replacement substrate; an active layer for
the converting radiation to electrical energy comprising at least
one lateral p-i-n structure; optionally, the active layer comprises
one or more rare-earth ions and a barrier layer comprising at least
one rare earth separating the active layer and the replacement
substrate.
[0120] An integrated device for converting radiation to electrical
energy comprises a replacement substrate; one or more active layers
for the converting radiation to electrical energy comprising
multiple devices interconnected such that there are a plurality of
devices for supplying a voltage interconnected; and a plurality of
devices for supplying a current interconnected; optionally, the
active layer comprises one or more different rare-earth ions and a
barrier layer comprising at least one rare earth separating the
active layer and the replacement substrate.
[0121] In one embodiment a device for converting radiation to
electrical energy comprises a first portion of a first conductivity
type at a first level of doping; a second portion of first
conductivity type at a second level of doping less than the first,
wherein a first drift voltage is imposed across the second portion;
a third portion of first conductivity type at about the first level
of doping; a fourth portion of first conductivity type at about the
second level of doping, wherein a second drift voltage is imposed
across the fourth portion; a fifth portion of second conductivity
type at a third level of doping; such that the second portion is a
drift region and the fourth portion is an avalanche region and
electrons undergo avalanche multiplication in the avalanche region
based upon the first drift voltage imposed across the second
portion and the second drift voltage imposed across the fourth
portion; a replacement substrate; optionally at least one portion
comprises one or more rare-earth ions; alternatively, the first and
second drift voltages are set as a function of the energy of said
radiation being converted; alternatively, at least said second and
fourth portions comprise a semiconductor material comprising an
indirect bandgap and a barrier layer comprising at least one rare
earth separating the active layer and the replacement
substrate.
[0122] In one embodiment a device for converting radiation to
electrical energy comprises a first portion of a first conductivity
type at a first level of doping; a second portion of first
conductivity type at a second level of doping less than the first,
wherein a drift voltage is imposed across the second portion; a
third portion of second conductivity type at a third level of
doping; such that the second portion is a drift and avalanche
region wherein electrons undergo avalanche multiplication based
upon the drift voltage imposed across the second portion;
alternatively, at least said second portion comprises a
semiconductor material comprising an indirect bandgap; optionally,
at least one portion comprises one or more rare-earth ions;
optionally said drift voltage is set as a function of the energy of
said radiation being converted; in some embodiments, at least about
50% of said electrical energy is converted from radiation of
wavelength 400 nm and shorter and a barrier layer comprising at
least one rare earth separating the active layer and the
replacement substrate.
[0123] In one embodiment a device for converting radiation to
electrical energy comprises, optionally, a replacement substrate;
one or more layers of a large band gap material; and one or more
layers of a small band gap material for converting radiation to
electrical energy, such that a layer of the large band gap material
are contacting a layer of the small band gap material; and the
large band gap material chosen from a group comprising rare-earth
oxide (RE.sub.xO.sub.z), rare-earth germanium oxide
(RE.sub.xGe.sub.yO.sub.z), rare-earth silicon oxide
(RE.sub.xSi.sub.yO.sub.z), rare-earth-silicon-oxide-phosphide
(RE.sub.xSi.sub.yO.sub.zP.sub.w), rare-earth-silicon-oxide-nitride
(RE.sub.xSi.sub.yO.sub.zN.sub.w),
rare-earth-silicon-oxide-nitride-phosphide
(RE.sub.xSi.sub.yO.sub.zN.sub.wP.sub.q) wherein X, Z>0 and Y, W.
Q are .gtoreq.0; and a barrier layer comprising at least one rare
earth separating the active layer and the replacement
substrate.
[0124] In one embodiment a device for converting radiation to
electrical energy comprises, optionally, a replacement substrate;
one or more layers of a large band gap material; and one or more
layers of a small band gap material for converting radiation to
electrical energy, such that the one or more layers of the large
band gap material are contacting a layer of the small band gap
material; and the large band gap material chosen from rare-earth
germanium oxide (RE.sub.xGe.sub.yO.sub.z) and a barrier layer
comprising at least one rare earth separating the active layer and
an optional replacement substrate.
[0125] In one embodiment a device for converting radiation to
electrical energy comprises a substrate; one or more layers of a
large band gap material; and one or more layers of a small band gap
material for converting radiation to electrical energy, such that
the one or more layers of the large band gap material are
contacting a layer of the small band gap material; and the large
band gap material chosen from rare-earth silicon oxide
(RE.sub.xSi.sub.yO.sub.z) and a barrier layer comprising at least
one rare earth separating the active layer and the replacement
substrate.
[0126] In one embodiment a device for converting radiation to
electrical energy comprises, optionally, a replacement substrate;
one or more layers of a large band gap material; and one or more
layers of a small band gap material for converting radiation to
electrical energy, such that the one or more layers of the large
band gap material are contacting a layer of the small band gap
material; and the large band gap material chosen from
rare-earth-silicon-oxide-phosphide (RE.sub.xSi.sub.yO.sub.zP.sub.w)
and a barrier layer comprising at least one rare earth separating
the active layer and an optional replacement substrate.
[0127] In one embodiment a device for converting radiation to
electrical energy comprises, optionally, a replacement substrate;
one or more layers of a large band gap material; and one or more
layers of a small band gap material for converting radiation to
electrical energy, such that the one or more layers of the large
band gap material are contacting a layer of the small band gap
material; and the large band gap material chosen from
rare-earth-silicon-oxide-nitride (RE.sub.xSi.sub.yO.sub.zN.sub.w)
and a barrier layer comprising at least one rare earth separating
the active layer and the replacement substrate.
[0128] In one embodiment a device for converting radiation to
electrical energy comprises, optionally, a replacement substrate;
one or more layers of a large band gap material; and one or more
layers of a small band gap material for converting radiation to
electrical energy, such that the one or more layers of the large
band gap material are contacting a layer of the small band gap
material; and the large band gap material chosen from
rare-earth-silicon-oxide-nitride-phosphide
(RE.sub.xSi.sub.yO.sub.zN.sub.wP.sub.q) and a barrier layer
comprising at least one rare earth separating the active layer and
the replacement substrate.
[0129] In one embodiment a device for converting radiation to
electrical energy comprises, optionally, a replacement substrate;
one or more layers of a large band gap material; and one or more
layers of a small band gap material for converting radiation to
electrical energy, such that the one or more layers of the large
band gap material are contacting a layer of the small band gap
material; and the small band gap material chosen from a group
comprising rare-earth-silicon (RE.sub.xSi.sub.y),
rare-earth-germanium (RE.sub.xGe.sub.y), rare-earth-phosphide
(RE.sub.xP.sub.y), rare-earth-nitride (RE.sub.xN.sub.y) such that
the small band gap is less than about 3 eV and, optionally, a
barrier layer comprising at least one rare earth separating the
active layer and an optional replacement substrate. In alternative
embodiments a small band gap may be less than about 2.5 eV;
optionally, a small band gap may be less than about 2.0 eV;
optionally, a small band gap may be less than about 1.5 eV;
optionally, a small band gap may be less than about 1.0 eV.
[0130] In one embodiment a device for converting radiation to
electrical energy comprises, optionally, a replacement substrate;
one or more layers of a large band gap material; and one or more
layers of a small band gap material for converting radiation to
electrical energy, such that the one or more layers of the large
band gap material are contacting a layer of the small band gap
material; and the small band gap material chosen from
rare-earth-germanium (RE.sub.xGe.sub.y) and a barrier layer
comprising at least one rare earth separating the active layer and
the replacement substrate. In one embodiment a device for
converting radiation to electrical energy comprises, optionally, a
replacement substrate; one or more layers of a large band gap
material; and one or more layers of a small band gap material for
converting radiation to electrical energy, such that the one or
more layers of the large band gap material are contacting a layer
of the small band gap material; and the narrow band gap material
chosen from rare-earth-phosphide (RE.sub.xP.sub.y) and a barrier
layer comprising at least one rare earth separating the active
layer and the replacement substrate. In one embodiment a device for
converting radiation to electrical energy comprises, optionally, a
replacement substrate; one or more layers of a large band gap
material; and one or more layers of a small band gap material for
converting radiation to electrical energy, such that the one or
more layers of the large band gap material are contacting a layer
of the small band gap material; and the narrow band gap material
chosen from rare-earth-nitride (RE.sub.xN.sub.y) and a barrier
layer comprising at least one rare earth separating the active
layer and the replacement substrate.
[0131] As used herein a replacement or alternative substrate is
optionally a substrate chosen from a group comprising glass, float
glass, quartz, alkali-silicate glass, plastics, including polyimide
and Kapton, flexible plastics, insulative coated metal, ceramic,
recycled silicon wafers, silicon ribbon, poly-silicon wafers or
substrates and other low cost substrates known to one knowledgeable
in the art. A replacement substrate takes the place of an original
substrate after the fabrication of an active layer upon an original
substrate; by means of a "layer transfer process" an active layer
is transferred from an original substrate to a replacement
substrate; additional processing may be performed after the
transfer to complete device fabrication.
[0132] As used herein an active layer comprises one or more layers
of semiconducting, insulative and/or metallic materials sufficient
to enable a solar cell or other thin film solid state device as
disclosed herein. An "active layer" is fabricated originally on a
substrate different than a replacement substrate; an active layer
is transferred to a replacement substrate by a method disclosed
herein or by reference disclosed herein or by techniques known to
one knowledgeable in the art.
[0133] In one embodiment a device for converting radiation to
electrical energy comprises at least one single crystal Si thin
film layer and one layer comprising a rare-earth in an active
region and one layer comprising a rare-earth in a barrier layer. In
one embodiment a device for converting radiation to electrical
energy comprises a MIS device on SoG.
[0134] In one embodiment a device for converting radiation to
electrical energy comprises a PIN device on SoG; alternatively a
PINPIN dual diode on SoG using different thickness i-regions to
efficiently absorb different portions of the solar spectrum is a
device for converting radiation to electrical energy;
alternatively, a MIS/PIN hybrid device on SoG is a device for
converting radiation to electrical energy; alternatively, a SoG
device with a barrier layer may be combined with one or more sun
concentrators.
[0135] In some embodiments a semiconductor device comprises a
substrate, one or more layers of a semiconductor device and a
barrier layer comprising one or more layers wherein at least one is
chosen from a group comprising rare-earth sesquioxide (RE2O3),
rare-earth dioxide (REO2), rare-earth monoxide (REO), rare-earth
nitride (REN), rare-earth oxynitride (REOxNy), rare-earth phosphide
(REP), rare-earth oxyphosphide (REOxPy), rare-earth carbide (RECy),
rare-earth oxycarbide (REOxCy), aluminium rare-earth oxide
(RExAlyOw), rare-earth aluminosilicate (RExAlySizOw), rare-earth
ternaries, such as, SiErN, SiErP, GeLAN, GeLaP, SiGeErn, SiGeErP,
aluminium oxide (Al2O3), silicon nitride (SiNx), (SixAlyNz),
Hf-oxide and HfON, Zr-oxide and ZrON, MgO and combinations thereof;
in some embodiments a barrier layer and/or substrate may undergo a
surface treatment such as a surface treatment of Al.sub.2O.sub.3
via nitridation, forming AlN interlayer, chlorination,
phosphorization, and/or treatment with a boron compound.
[0136] FIG. 24A discloses process steps 1001 through 1009, required
for the formation of thin film layer upon sacrificial layer and
subsequent separation. First, the parent substrate 1021 is cleaned
and prepared for epitaxy. In one embodiment the substrate 1021 is
chosen from single crystal silicon with (100)-, (111)- or
(110)-oriented surface. Next, a substantially single crystal
sacrificial epitaxial layer 1022 is deposited with predetermined
thickness; thickness may range from 10 nm to 10 microns depending
upon composition and process parameters. The thin film
semiconductor layer 1023 is directly deposited upon the sacrificial
layer 1022. The thin film semiconductor layer is also substantially
single crystal and uniform in thickness. In one embodiment, the
sacrificial layer is chosen from a rare-earth based compound of the
form RE.sub.xO.sub.yN.sub.zP.sub.w; 0.ltoreq.y, z, w.ltoreq.5,
0<x.ltoreq.5. A thin film semiconductor layer is chosen from
silicon, germanium or silicon-germanium alloy; Alternatively, a
thin film semiconductor layer is chosen from Group IV, Group III-V,
or Group II-VI materials or combinations thereof. Alternatively, a
semiconductor substrate, primary or secondary is chosen from Group
IV, Group III-V, or Group II-VI materials or combinations
thereof.
[0137] The completed composite single crystal article 1020 is then
subjected to selective layer process 1024. FIG. 24B, Step 1005
schematically shows the structural and/or chemical modification of
selective process 1024 on the sacrificial layer 1022. The region
1025 depicts the selective modification of layer 1022 into new form
1025. The lateral transport and/or diffusion and/or reaction of
process 1024 results in region 1025 extending into the interior of
the composite article confined in a region occupied by the initial
layer 1022.
[0138] The lateral selective modification of the sacrificial layer
1022 is continued until the entirety of layer 1022 is modified,
thereby forming new uniform layer 1025. The parent substrate and
thin film semiconductor layer are substantially unaffected by
process 1024. FIG. 24C depicts the removal of layer 1022 and 1025
such that the thin film layer 1023 is physically separated 1026
from the parent substrate 1021.
[0139] The result of process 1024 on layer 1022 may consume the
constituent atoms comprising layer 1022 and be removed during
processing. Alternately, layer 1022 may undergo a structural phase
change due to process 1024, for example transform from single
crystal structure to amorphous or porous or nanocrystalline or
microcrystalline or powder form. Another selective removal process
may be required to remove resultant layer or form 1025.
[0140] The utility of the aforementioned method is via parallel
processing of thin film article with an alternative substrate prior
to thin film layer separation.
[0141] FIGS. 25A, 25B, 25C and 3 disclose schematic processing
steps required for the formation of thin film semiconductor on
alternative substrate.
[0142] First, the single crystal thin film 2023 and sacrificial
layer 2022 are deposited via direct epitaxy on parent substrate
2021. An optional interfacial bonding layer (IBL) 2024 with surface
2025 suitable for bonding to alternative substrate may be also
deposited. The IBL does not need to be single crystal and can be
deposited ex-situ prior to wafer bonding to alternative substrate
2027. The alternative substrate 2027 is cleaned and prepared 2005
with bonding surface 2026 optionally coated with layer 2028.
Optionally, the alternative substrate coated with layer 2028 may
result in predetermined warpage of substrate 2027. Step 2007 shows
convex surface bowing due to predetermined film stress 2028 or
concave warpage in 2008. If alternative substrate is geometrically
modified by layer 2028, then surface 2032 or 2033 is used for
intimate contact with final exposed surface of 2023 or 2024.
[0143] For clarity, the following process steps are described
without alternative substrate geometry modification. FIG. 25B
schematically describes the physical joining 2029 and subsequent
bonding of surfaces 2026 and 2025 forming composite article 2031
comprising parent substrate 2021, sacrificial layer 2022, thin film
semiconductor layer 2023, IBL 2024 and alternative substrate 2027.
The wafer bonding process is performed such that the surfaces 2025
and 2026 when in contact are free from contamination, particulate
and voids, forming a well defined and homogeneous interface.
[0144] FIG. 25C schematically described the selective and lateral
modification of the sacrificial layer 2022 by process 2040. The
initial process 2011 is continued until the sacrificial layer is
consumed and/or modified in entirety. The lateral process
completing at the center of the composite article, thereby forming
uniform region 2041 in step 2013. Other than the sacrificial layer
2022, all other layers and substrate are substantially unaffected
by process 2040.
[0145] FIG. 26 schematically describes the possible layer
separation paths. The selective layer modification of 2022 into
2041 results in composite article 3000. Process 2040 or by the
action of subsequent mechanical or chemical or reactive process
provides a physical separation of the thin film semiconductor layer
2023 from the parent substrate 2021. The thin film semiconductor
layer is bonded to alternative substrate. In one embodiment, thin
film semiconductor layer 2023 is chosen from single crystal
silicon, germanium or silicon-germanium alloy; in alternative
embodiments a substrate may be chosen from a group comprising
sapphire, silicon carbide, III-V compounds, and II-VI compounds.
The parent substrate 2021 is chosen from single crystal silicon
substrate. The alternative substrate is chosen from amorphous
material such as glass, Pyrex.TM., metal foil, metal substrate
and/or flexible substrate. Process paths 3001, 3002 and 3003 all
result in thin film semiconductor on alternate substrate 2027.
Process path 3001 shows residual sacrificial layer 2041 can be
substantially, completely separated from thin film semiconductor
layer 2023 upon physical separation. Alternately, a portion of
layer 2041 remains in contact with the surface of layer 2023, as
shown in process path 3002.
[0146] FIG. 27 discloses an embodiment for sacrificial layer
composition and the possible selective process reactions for
modification of the composition and crystallographic structure. The
sacrificial layer is composed of rare-earth oxide (RE.sub.2O.sub.3
or REO.sub.2 or generally RE.sub.yO.sub.x, where 0<x,
y.ltoreq.5) and can be deposited in single crystal form on silicon
or other substrates. By way of example, and not limited to,
rare-earth oxide crystals readily undergo chemical reaction with
hydrogen, water and carbon-dioxide. Other reactions are also
possible and are incorporated herein. For example, single crystal
rare-earth oxide can be hydrated 4007 by immersion of REO.sub.x
4001 in water H.sub.2O.sub.(1) and/or reacted with steam
H.sub.2O.sub.(g) 4004. Typically, single crystal REO.sub.x,
x.apprxeq.1.5, reacts with water to form hydrated clusters
RE.sub.2O.sub.x(H.sub.2O).sub.y thereby destroying the single
crystal structure. Other reactions such as hydrogenation 4005 and
carbonization 4006 are possible with reactant products shown.
Hydrogenation 4005 by reacting REO.sub.x 4001 with H.sub.2(g) 4002
forms rare-earth hydroxyl compounds. Carbonization occurs by
reacting REO.sub.x with gaseous carbon, forming rare-earth carbide
or oxy-carbide compounds.
[0147] The processes of hydration 4007, hydrogenation 4005 and
carbonization 4006 of single crystal rare-earth oxide 4001 results
in morphological change in structure. For example, single crystal
REOx can be transformed into amorphous or polycrystalline granules
with increase in volume. This process is advantageous for cleaving
of composite article 3000 into at least one of process paths 3001,
3002, and 3003.
[0148] An alternative method for layer separation using rare-earth
oxide sacrificial layer is via use of inherent catalyst function,
as shown in FIG. 28. Rare-earth oxide compound layer 5002 is
deposited as sacrificial layer as single crystal structure as
described in the present invention. The REO.sub.x can behave as a
catalyst when reacted with incident gaseous compounds R.sub.A and
R.sub.B 5006 transforming input gaseous species into a new compound
R.sub.c 5008 through catalytic action of REO.sub.x 5002 and
consuming reactants R.sub.A & R.sub.B 5006. The single crystal
sacrificial layer 5002 is not chemically consumed in the catalytic
reaction but the process does modify the crystal structure from
homogeneous single crystal layer into non-uniform fragments of REOx
regions 5009. For example, FIG. 29 shows the catalytic process of
reactants R.sub.A & R.sub.B 6003 transforming into byproduct
R.sub.c 6006 via catalyst REOx 6002. The long range order of the
REOx crystal structure is destroyed during the process forming
disordered polycrystalline REO.sub.x in the form of granules,
micro-crystalline, nanocrystalline or powder. That is, the REOx
epitaxial layer 6002 is structurally destroyed or modified 6007 by
action of the catalytic process 6003/6004/6005.
[0149] Rare-earth oxides crystallize as fluorite or bixbyite
crystallographic structures, depending upon the specific RE species
chosen. Both fluorite (REO.sub.2) and bixbyite (RE.sub.2O.sub.3)
rare-earth oxide crystals exhibit defects, such as oxygen or metal
vacancies or interstitials. Oxygen vacancies allow the relatively
free transport of oxygen and/or other atomic or diatomic species or
molecular species through the bulk of the REO.sub.x crystal. For
example, O, N, H, C, P, O.sub.2, N.sub.2O, H.sub.2O, CO.sub.2,
H.sub.2, P.sub.2, PH.sub.3, etc. may penetrate the single crystal
REO.sub.x structure. Furthermore, RE.sub.yO.sub.x single crystals
may possess defects such as oxygen vacancies preferentially aligned
along crystallographic axes, allowing long range transport through
the bulk of the crystal. This property is advantageous for the
present invention for use as layer separation mechanism.
[0150] Another example of sacrificial layer separation using
rare-earth based material is via selective etching and/or removal
of the sacrificial layer 7002 via process gases or liquids or
reagents or reactive species 7003, as shown in FIG. 30. As the
sacrificial layer is consumed 7004 by formation of reactants 7005
the layer 7002 is ultimately removed from the surface of the
substrate 7001. This process is shown as step 1009 in FIG. 24C and
results in the layer separation of thin film semiconductor onto
alternative substrate.
[0151] The advantage of the present invention is that optimized
growth of the initial single crystal article can be accomplished
independent of the alternative substrate. The single crystal
article, for example 2031, comprising thin film semiconductor on
single crystal rare-earth oxide layer deposited upon parent
substrate can be fabricated prior to wafer bonding alternate
substrate. The selective removal and/or modification of the single
crystal sacrificial layer can be performed at conditions suitable
for processing alternative substrate composite article. That is, a
low thermal budget process such as steam hydration can be used to
perform thin film layer separation.
[0152] In one embodiment, single crystal silicon substrates are
utilized as the primary or parent substrate. The substantially
single crystal sacrificial layer is formed using the general
compound of rare-earth-oxygen-nitrogen-phosphorus-carbon of general
chemical formula RE.sub.xO.sub.yN.sub.zP.sub.wC.sub.v.
Alternatively, thin film semiconductor layers may be chosen from
Si, Ge, or SiGe alloys, GaAs, GaN, InN, InP, SiC or alternative
Group IV, Group III-V or Group II-VI semiconductors; alternatively,
a semiconductor substrate, primary or secondary is chosen from
Group IV, Group III-V, or Group II-VI materials or combinations
thereof.
[0153] Thin film semiconductor devices can be patterned laterally
upon alternative substrate using selective area epitaxy of
crystalline sacrificial layer and removal of the same. FIGS. 31,
32, 33 and 34 describe the selective area thin film device
manufacture on alternative substrate. FIG. 31 shows the selective
area epitaxy of sacrificial layer 8004 disposed upon single crystal
parent substrate 8006. For example, the selective areas 8004 in
step 8100 may be deposited and patterned by use of a shadow mask
8002 position between the source material flux 8001 and the parent
substrate surface 8006. Step 8200 shows the thin film crystalline
semiconductor 8011 blanket deposited 8010 upon the patterned parent
substrate comprising selective areas of crystalline sacrificial
regions 8004. The thin film semiconductor layer (not necessarily
the same composition as the parent substrate) is deposited with
thickness substantially comprising uniform crystalline structure
and thickness in regions where direct epitaxy on sacrificial layer
occurs.
[0154] For the case of homo-epitaxy of semiconductor upon parent
substrate, the crystal quality will also be high. The thin film
semiconductor layer thickness 8012 is substantially the same for
direct epitaxy on parent substrate and sacrificial layer surfaces.
Generally, the sacrificial layer thickness 8005 is thicker than the
thin film semiconductor layer thickness 8012.
[0155] FIG. 32 step 8300 shows the wafer bonding 8013 of
alternative substrate surface 8012 with regions formed by thin film
semiconductor layer surface 8011 deposited upon sacrificial layer
8004. The joined article 8200 in step 8400 comprises alternative
substrate and selective area patterned thin film regions with
intentional voids between alternative substrate and thin film
semiconductor regions deposited directly upon parent substrate.
FIG. 33 step 8500 schematically depicts the selective area
modification and or removal 8014 of the sacrificial layer 8004 via
material selective process 8015. Step 8600 results in physical
layer separation by virtue of sacrificial layer removal into
desired selective area thin film semiconductor on alternative
substrate article 9001 and remaining patterned parent substrate
9002.
[0156] The separated parent substrate containing patterned thin
film semiconductor regions 9002 can be recycled directly for use in
step 8200, bypassing the need for step 8100.
[0157] FIG. 34 step 8700 shows the released completed thin film
semiconductor on alternative substrate article comprising patterned
thin film semiconductor region 8011. Regions 8011 may be single
crystal or polycrystal or combinations thereof. Step 8800
schematically shows subsequent processing to produce thin film
electron or optoelectronic devices 8016 disposed upon alternative
substrate.
[0158] A multi-junction solar cell can be fabricated using
amorphous-crystalline (a-c) semiconductors via the present
invention. However, the effective band gap of an amorphous
semiconductor is typically larger relative to the single crystal
semiconductor form. Hetero-junction formation between the same
chemical composition materials but dissimilar structural forms,
such as amorphous and single crystalline semiconductor, offer
improved optical response for solar cell device. For example,
amorphous Si (a-Si) exhibits an effective band gap of
1.5.ltoreq.E.sub.g(a-Si).ltoreq.2.0 eV, compared to crystalline Si
(c-Si) with E.sub.g (c-Si)=1.1 eV.
[0159] FIG. 35 shows processing steps for further deposition of
thin film semiconductors upon the selective area patterned single
crystal regions formed on amorphous substrate 8012. For example,
the alternative substrate is transparent to solar radiation and
comprised of glass. The thin film semiconductor 8011 is chosen from
Si or Ge and formed using the sacrificial layer separation
technique described herein.
[0160] Further epitaxy or deposition upon the article in step 9100
results in new thin film layers disposed upon amorphous substrate
8012 or single crystal semiconductor regions 8011, as shown in step
9200. For example, the thin film semiconductor 8011 is chosen from
single crystal Si and further epitaxy of the same species during
subsequent deposition 9020 forms single crystal regions 9030 seeded
by region 8011 and amorphous regions 9025 deposited upon amorphous
substrate 8012. The deposited layers can be chosen to exhibit
different conductivity type, such as n-type or p-type. For example,
thin film layer 8011 can be deposited as n-type Si and subsequent
processing in step 9200 can deposit p-type c-Si 9030 and p-type
a-Si 9025. The regions can be metallized to form electrical
contacts to the p-type Si region 9030 via contact 9031 and p-type
a-Si region 9025 via electrode 9026.
[0161] The deposition process used for layers 9025 and 9030 can be
via different process, for example, PECVD, CVD and the like,
forming hydrogenated amorphous Si (H:a-Si). The hydrogen content
can be used as an effective means for passivating junctions between
9025/8011 and surfaces of 9030. The resulting structure of FIG. 13
comprises a p/n diode c-Si junction and p-type a-Si/n-type c-Si
junction. The band gap energy variation as a function of direction
parallel (x) and perpendicular (y) to the plane of the alternative
substrate. The wide band gap a-Si region 9025 forms a structural
heterojunction with the c-Si region 8011. The p-type 9030 and
n-type 8011 c-Si homojunction forms a p/n diode.
[0162] Operation of structure in FIG. 36 as solar cell energy
conversion device is achieved by orienting structure such that
solar radiation is incident in a direction substantially from the
alternative substrate surface into the active thin film
semiconductor layers. The metallization/electrodes can behave as
reflectors enabling multi-pass reflection in thin film layers. The
a-Si region is responsive to higher energy photons (shorter
wavelength .about.600 nm) and the c-Si is responsive to lower
energy photons (in the vicinity of the indirect band gap absorption
edge>1 eV, i.e. .about.1200 nm). The vertical and horizontal
diodes formed by the present invention constitutes a two junction
solar cell with solar cell efficiency exceeding that from single
junction c-Si p/n solar cell.
[0163] In one embodiment a solar cell device for converting
radiation to electrical energy comprises an active layer for the
converting comprising at least a large band gap material and a
small band gap material and an optically transparent conducting
oxide over at least a portion of the surface of the active layer
first receiving the radiation.
[0164] In some embodiments a device for converting radiation to
electrical energy comprises; active layer for converting incident
radiation to electrical energy comprising a Group IV semiconductor;
transparent substrate; and transparent barrier layer consisting of
one or more a rare earth compounds; wherein the barrier layer
separates the active layer and the substrate and substantially
prevents unwanted ions from the substrate migrating to the active
layer wherein the active layer comprises one or more layers of a
large band gap material; and one or more layers of a small band gap
material; wherein the large band gap material is chosen from a
group consisting of rare-earth oxide (RE.sub.xO.sub.z), rare-earth
germanium oxide (RE.sub.xGe.sub.yO.sub.z), rare-earth silicon oxide
(RE.sub.xSi.sub.yO.sub.z), rare-earth-silicon-oxide-phosphide
(RE.sub.xSi.sub.yO.sub.zP.sub.w), rare-earth-silicon-oxide-nitride
(RE.sub.xSi.sub.yO.sub.zN.sub.w),
rare-earth-silicon-oxide-nitride-phosphide
(RE.sub.xSi.sub.yO.sub.zN.sub.wP.sub.q) wherein X, Z>0 and Y, W,
Q are .gtoreq.0, such that the band gap is greater than about 3 eV
and wherein said small band gap material is chosen from a group
consisting of rare-earth-silicon (RE.sub.xSi.sub.y),
rare-earth-germanium (RE.sub.xGe.sub.y), rare-earth-phosphide
(RE.sub.xP.sub.y), and rare-earth-nitride (RE.sub.xN.sub.y) and
mixtures thereof and wherein X, Y>0 and said small band gap is
less than about 3 eV; optionally, the active layer comprises at
least one lateral p-n junction; optionally, the barrier layer
consists of one or more rare earth compounds and charged oxygen
vacancies, (O.sub.y.sup.n), such that migration of alkaline ions
across said barrier layer is functionally impeded; optionally, the
barrier layer comprises at least two layers wherein at least one of
the at least two layers has a band gap greater than about 3 eV;
optionally, the active layer comprises one or more layers of a
large band gap material; and one or more layers of a small band gap
material; wherein the large band gap material is chosen from a
group consisting of rare-earth oxide (RE.sub.xO.sub.z), rare-earth
germanium oxide (RE.sub.xGe.sub.yO.sub.z), rare-earth silicon oxide
(RE.sub.xSi.sub.yO.sub.z), rare-earth-silicon-oxide-phosphide
(RE.sub.xSi.sub.yO.sub.zP.sub.w), rare-earth-silicon-oxide-nitride
(RE.sub.xSi.sub.yO.sub.zN.sub.w),
rare-earth-silicon-oxide-nitride-phosphide
(RE.sub.xSi.sub.yO.sub.zN.sub.wP.sub.q) wherein X, Z>0 and Y, W,
Q are .gtoreq.0, such that the band gap is greater than about 3 eV;
optionally, the transparent barrier layer consists of one or more
rare earth compounds and at least one charged oxygen vacancy,
(O.sub.y.sup.n; optionally, the small band gap material is chosen
from a group consisting of rare-earth-silicon (RE.sub.xSi.sub.y),
rare-earth-germanium (RE.sub.xGe.sub.y), rare-earth-phosphide
(RE.sub.xP.sub.y), and rare-earth-nitride (RE.sub.xN.sub.y) and
mixtures thereof and wherein X, Y>0 and said small band gap is
less than about 3 eV; optionally, the transparent barrier layer
comprises a first and second layer wherein the first layer is in
contact with the transparent substrate and the second layer is in
contact with the active layer and wherein at least one of the first
layer and second layer consists of one or more compounds chosen
from a group consisting of calcium oxide (CaO), sodium oxide
(Na.sub.2O), potassium oxide (K.sub.2O), aluminum oxide
(Al.sub.2O.sub.3), boron oxide (B.sub.2O.sub.3), zirconium oxide
(ZrO.sub.2), zircon (ZrSiO.sub.4), lead oxide (PbO), alkaline earth
metal oxides (AEOx), phosphate glass, phosphorous silicate glass,
rare-earth sesquioxide (RE.sub.2O.sub.3), rare-earth dioxide
(REO.sub.2), rare-earth monoxide (REO), rare-earth nitride (REN),
rare-earth oxynitride (REO.sub.xN.sub.y), rare-earth phosphide
(REP), rare-earth oxyphosphide (REO.sub.xP.sub.y), rare-earth
carbide (REC.sub.y), rare-earth oxycarbide (REO.sub.xC.sub.y),
aluminum rare-earth oxide (RE.sub.xAl.sub.yO.sub.w), rare-earth
aluminosilicate (RE.sub.xAl.sub.ySi.sub.zO.sub.w), silicon nitride
(SiN.sub.x), (Si.sub.xAl.sub.yN.sub.z), N:Al.sub.2O.sub.3, aluminum
oxynitride (AlO.sub.xN.sub.y), aluminum nitride (AlN.sub.x),
silicon-aluminum-oxynitride (Si.sub.zAl.sub.yO.sub.xN.sub.y),
silicon-carbon-nitride (Si.sub.zC.sub.xN.sub.y),
aluminum-carbon-oxynitride (Al.sub.zC.sub.yO.sub.xN.sub.y),
silicon, SiO.sub.x, rare-earth material, germanium and mixtures of
silicon-germanium and combinations and non-stoichiometric
combinations thereof; optionally, the transparent barrier layer
comprises a first and second layer wherein the first layer is in
contact with the transparent substrate and the second layer is in
contact with the active layer and wherein the first layer consists
of one or more a compounds described by
[RE].sub.x[RE].sub.y[RE].sub.z[C].sub.m[O].sub.n[N].sub.p[P].sub.r[Si].su-
b.s[Ge].sub.t[Al].sub.u wherein x>0 and at least one of y, z, m,
n, p, r, s, t, or u are >O and RE is a rare earth; optionally,
the transparent substrate is chosen from a group consisting of
sapphire, aluminum oxide (Al.sub.2O.sub.3), diamond (C.sub.4),
calcium fluoride (CaF.sub.2), zircon (Zr.sub.xSi.sub.1-xO.sub.4),
zinc oxide (ZnO), aluminum nitride (AlN), glass, sodium-silicate
glass (Na.sub.2O).sub.x.(SiO.sub.2).sub.1-x, alkali-metal oxides
(AMO.sub.x), alkaline-earth metal oxides, a ceramic and
crystallized bauxite; optionally, the transparent barrier layer
comprises a transparent conducting oxide layer; optionally, the
transparent substrate is flexible.
[0165] In some embodiments a device for converting radiation to
electrical energy comprises an active layer for the converting
radiation to electrical energy comprising a first semiconductor
layer of first conductivity type of thickness between about 30 nm
and 150 nm; a second semiconductor layer of second conductivity
type of thickness between about 30 nm and 150 nm; a transparent
barrier layer consisting of one or more a rare earth compounds; and
a substrate transparent to a majority of the radiation for
converting, wherein the barrier layer separates the active layer
and the substrate such that migration of deleterious species across
the barrier layer is functionally impeded and wherein the first and
second semiconductor layers comprise one or more layers of a large
band gap material; and one or more layers of a small band gap
material; wherein the large band gap material is chosen from a
group consisting of rare-earth oxide (RE.sub.xO.sub.z), rare-earth
germanium oxide (RE.sub.xGe.sub.yO.sub.z), rare-earth silicon oxide
(RE.sub.xSi.sub.yO.sub.z), rare-earth-silicon-oxide-phosphide
(RE.sub.xSi.sub.yO.sub.zP.sub.w), rare-earth-silicon-oxide-nitride
(RE.sub.xSi.sub.yO.sub.zN.sub.w),
rare-earth-silicon-oxide-nitride-phosphide
(RE.sub.xSi.sub.yO.sub.zN.sub.wP.sub.q) wherein X, Z>0 and Y, W,
Q are .gtoreq.0, such that the band gap is greater than about 3 eV
and wherein said small band gap material is chosen from a group
consisting of rare-earth-silicon (RE.sub.xSi.sub.y),
rare-earth-germanium (RE.sub.xGe.sub.y), rare-earth-phosphide
(RE.sub.xP.sub.y), and rare-earth-nitride (RE.sub.xN.sub.y)
and_mixtures thereof and wherein X, Y>0 and said small band gap
is less than about 3 eV; optionally, the substrate is chosen from a
group consisting of sapphire, aluminum oxide (Al.sub.2O.sub.3),
diamond (C.sub.4), calcium fluoride (CaF.sub.2), zircon
(Zr.sub.xSi.sub.1-xO.sub.4), zinc oxide (ZnO), aluminum nitride
(AlN), glass, sodium-silicate glass
(Na.sub.2O).sub.x.(SiO.sub.2).sub.1-x, alkali-metal oxides
(AMO.sub.x), alkaline-earth metal oxides, a ceramic and
crystallised bauxite; optionally, the barrier layer comprises one
or more layers wherein at least one of the one or more layers is
chosen from a group consisting of calcium oxide (CaO), sodium oxide
(Na.sub.2O), potassium oxide (K.sub.2O), aluminum oxide
(Al.sub.2O.sub.3), boron oxide (B.sub.2O.sub.3), zirconium oxide
(ZrO.sub.2), zircon (ZrSiO.sub.4), lead oxide (PbO), alkaline earth
metal oxides (AEOx), phosphate glass, phosphorous silicate glass,
rare-earth sesquioxide (RE.sub.2O.sub.3), rare-earth dioxide
(REO.sub.2), rare-earth monoxide (REO), rare-earth nitride (REN),
rare-earth oxynitride (REO.sub.xN.sub.y), rare-earth phosphide
(REP), rare-earth oxyphosphide (REO.sub.xP.sub.y), rare-earth
carbide (REC.sub.y), rare-earth oxycarbide (REO.sub.xC.sub.y),
aluminum rare-earth oxide (RE.sub.xAl.sub.yO.sub.w), rare-earth
aluminosilicate (RE.sub.xAl.sub.ySi.sub.zO.sub.w), silicon nitride
(SiN.sub.x), (Si.sub.xAl.sub.yN.sub.z), N:Al.sub.2O.sub.3, aluminum
oxynitride (AlO.sub.xN.sub.y), aluminum nitride (AlN.sub.x),
silicon-aluminum-oxynitride (Si.sub.zAl.sub.vO.sub.xN.sub.y),
silicon-carbon-nitride (Si.sub.zC.sub.xN.sub.y),
aluminum-carbon-oxynitride (Al.sub.zC.sub.vO.sub.xN.sub.y),
silicon, SiO.sub.x, rare-earth material, germanium and mixtures of
silicon-germanium and combinations and non-stoichiometric
combinations thereof; optionally, the active layer comprises a
composition chosen from at least one of silicon, germanium, and
carbon or mixtures thereof.
[0166] In some embodiments a device for converting radiation to
electrical energy comprises an active layer for the converting
radiation to electrical energy comprising a first semiconductor
layer of first conductivity type of thickness between about 30 nm
and 150 nm; a second semiconductor layer of second conductivity
type of thickness between about 30 nm and 150 nm; a transparent
barrier layer consisting of one or more rare earth compounds; and a
substrate transparent to a majority of the radiation for
converting, wherein the barrier layer separates the active layer
and the substrate such that migration of deleterious species across
the barrier layer is functionally impeded and wherein the first and
second semiconductor layers comprise one or more layers chosen from
a group consisting of germanium carbide (GeC.sub.x), germanium
nitride (GeN.sub.x), tin germanium (SnGe.sub.x), tin oxide
(SnO.sub.x), gallium phosphide (GaP), gallium nitride (GaNx),
indium nitride (InNx), aluminium nitride (AlNx), zinc oxide
(ZnO.sub.x), magnesium oxide (MgO.sub.x) and
Si.sub.ySn.sub.yGe.sub.zC.sub.w or combinations and
non-stoichiometric combinations thereof wherein 0<x.ltoreq.20
and 0<v, y, z.ltoreq.1 and 0.ltoreq.w.ltoreq.1; optionally, the
first and second semiconductor layers comprise one or more layers
chosen from a group consisting of Zn.sub.xMg.sub.yO.sub.zN.sub.w
and non-stoichiometric combinations thereof wherein at least one of
x or y is >0 and at least one of z or w is >0; optionally,
the first and second semiconductor layers comprise one or more
layers chosen from a group consisting of
In.sub.xGa.sub.yAl.sub.zN.sub.w and non-stoichiometric combinations
thereof wherein 0<w, y.ltoreq.1 and 0.ltoreq.x, z.ltoreq.1;
optionally, the barrier layer comprises at least two layers wherein
at least one of the at least two layers has a band gap greater than
about 3 eV; optionally, the transparent barrier layer comprises a
first and second layer wherein the first layer is in contact with
the transparent substrate and wherein the first layer or second
layer consists of one or more compounds chosen from a group
consisting of calcium oxide (CaO), sodium oxide (Na.sub.2O),
potassium oxide (K.sub.2O), aluminum oxide (Al.sub.2O.sub.3), boron
oxide (B.sub.2O.sub.3), zirconium oxide (ZrO.sub.2), zircon
(ZrSiO.sub.4), lead oxide (PbO), alkaline earth metal oxides
(AEOx), phosphate glass, phosphorous silicate glass, rare-earth
sesquioxide (RE.sub.2O.sub.3), rare-earth dioxide (REO.sub.2),
rare-earth monoxide (REO), rare-earth nitride (REN), rare-earth
oxynitride (REO.sub.xN.sub.y), rare-earth phosphide (REP),
rare-earth oxyphosphide (REO.sub.xP.sub.y), rare-earth carbide
(REC.sub.y), rare-earth oxycarbide (REO.sub.xC.sub.y), aluminum
rare-earth oxide (RE.sub.xAl.sub.yO.sub.w), rare-earth
aluminosilicate (RE.sub.xAl.sub.ySi.sub.zO.sub.w), silicon nitride
(SiN.sub.x), (Si.sub.xAl.sub.yN.sub.z), N:Al.sub.2O.sub.3, aluminum
oxynitride (AlO.sub.xN.sub.y), aluminum nitride (AlN.sub.x),
silicon-aluminum-oxynitride (Si.sub.zAlO.sub.xN.sub.y),
silicon-carbon-nitride (Si.sub.zC.sub.xN.sub.y),
aluminum-carbon-oxynitride (Al.sub.zC.sub.vO.sub.xN.sub.y),
SiO.sub.x, rare-earth material, mixtures of silicon-germanium and
combinations and non-stoichiometric combinations thereof;
optionally, the transparent barrier layer comprises a first and
second layer wherein the first layer is in contact with the
transparent substrate and wherein the first layer or second layer
consists of one or more compounds chosen from a group consisting of
[RE].sub.x[RE].sub.y[RE].sub.z[C].sub.m[O].sub.n[N].sub.p[P].sub.r[Si].su-
b.s[Ge].sub.t[Al].sub.u wherein x>0 and at least one of y, z, m,
n, p, r, s, t, or u are >0 and RE is a rare earth; optionally,
the transparent substrate is chosen from a group consisting of
sapphire, aluminum oxide (Al.sub.2O.sub.3), diamond (C.sub.4),
calcium fluoride (CaF.sub.2), zircon (Zr.sub.xSi.sub.1-xO.sub.4),
zinc oxide (ZnO), aluminum nitride (AlN), glass, sodium-silicate
glass (Na.sub.2O).sub.x.(SiO.sub.2).sub.1-x, alkali-metal oxides
(AMO.sub.x), alkaline-earth metal oxides, a ceramic and
crystallized bauxite.
[0167] Foregoing described embodiments of the invention are
provided as illustrations and descriptions. They are not intended
to limit the invention to precise form described. In particular, it
is contemplated that functional implementation of invention
described herein may be implemented equivalently. Alternative
construction techniques and processes are apparent to one
knowledgeable with integrated circuit, solar cell, flexible circuit
and MEMS technology. Other variations and embodiments are possible
in light of above teachings, and it is thus intended that the scope
of invention not be limited by this Detailed Description, but
rather by Claims following.
* * * * *