U.S. patent application number 16/505022 was filed with the patent office on 2020-01-30 for artificially engineered iii-nitride digital alloy.
The applicant listed for this patent is LEHIGH UNIVERSITY. Invention is credited to Wei SUN, Chee-Keong TAN, Nelson TANSU.
Application Number | 20200035790 16/505022 |
Document ID | / |
Family ID | 56849906 |
Filed Date | 2020-01-30 |
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United States Patent
Application |
20200035790 |
Kind Code |
A1 |
TANSU; Nelson ; et
al. |
January 30, 2020 |
ARTIFICIALLY ENGINEERED III-NITRIDE DIGITAL ALLOY
Abstract
A material structure and system for generating a III-Nitride
digital alloy.
Inventors: |
TANSU; Nelson; (Bethlehem,
PA) ; SUN; Wei; (Bethlehem, PA) ; TAN;
Chee-Keong; (Bethlehem, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LEHIGH UNIVERSITY |
Bethlehem |
PA |
US |
|
|
Family ID: |
56849906 |
Appl. No.: |
16/505022 |
Filed: |
July 8, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15061156 |
Mar 4, 2016 |
10347722 |
|
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16505022 |
|
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62128112 |
Mar 4, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 21/02507 20130101;
H01L 29/155 20130101; H01L 21/0254 20130101; H01L 21/02458
20130101; H01L 29/2003 20130101 |
International
Class: |
H01L 29/15 20060101
H01L029/15; H01L 21/02 20060101 H01L021/02; H01L 29/20 20060101
H01L029/20 |
Goverment Interests
STATEMENT REGARDING GOVERNMENT SUPPORT
[0002] This invention was made with government support under U.S.
National Science Foundation Award Nos. ECCS-1408051 and
DMR-1505122. The U.S. government has certain rights in the
invention.
Claims
1-20. (canceled)
21. A method for forming a III-Nitride optoelectronic device, the
method comprising: establishing a wavelength for the optoelectronic
device; providing first and second III-Nitride binary alloy
materials; and epitaxially layering the first and second
III-Nitride binary alloy materials proximate to each other with
thicknesses based on the established wavelength, wherein the first
and second III-Nitride binary alloy materials are different.
22. The method of claim 21, further comprising: epitaxially
layering, proximate to at least one of the first or the second
III-Nitride binary alloy materials, a third III-Nitride binary
alloy material that differs from the first and second III-Nitride
binary alloy materials to form a quaternary optoelectronic device,
wherein a thickness of the third III-Nitride binary alloy material
is based on the established wavelength.
23. The method of claim 21, wherein: the established wavelength is
selectable within a range of about 510 nanometers to about 1900
nanometers.
24. The method of claim 21, wherein: the established wavelength is
selectable within a range of about 240 nanometers to about 310
nanometers.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 15/061,156, filed Mar. 4, 2016, which claims priority under 35
U.S.C. .sctn. 119(e) to U.S. Provisional Patent Application Ser.
No. 62/128,112, filed Mar. 4, 2015, the entire content of which is
hereby incorporated herein by reference.
FIELD OF INVENTION
[0003] In general, the invention relates generally to III-Nitride
materials and fabrication methods. In more detail, the invention
relates to a material structure and method for generating a
III-Nitride digital alloy.
BACKGROUND
[0004] III-Nitride materials have been extensively studied and
implemented in advanced solid state lighting technologies in recent
decades. The III-Nitride platform has also attracted tremendous
efforts in developing high performance active region for
optoelectronic devices including detectors and solar energy
convertors. Specifically, the demand for integrating devices
covering a broad spectral regime in a single nitride-based material
platform drives the further pursuit of III-Nitride materials with a
tunable band gap property.
[0005] The identification of the narrow bandgap in InN binary
alloys (.about.0.64 eV) and large bandgap in AlN binary alloys
(.about.6 eV) has enabled access to broad energy gap coverage by
utilizing corresponding ternary and quaternary alloys with
different Indium (In)/Gallium (Ga)/Aluminum (Al) composition. For
example, varying the Indium (In) composition in InGaN ternary alloy
from very low to high In-content provides the ability to cover a
broad optical regime from .about.3.4 eV (GaN) to .about.0.64 eV
(InN). Similarly, tuning the Aluminum (Al) composition in the AlGaN
ternary alloy allows the transition energy to change from
.about.3.4 eV (GaN) to .about.6 eV (AlN).
[0006] The InGaN ternary alloy with high In content has been
recognized for its importance in achieving optical emission and
absorption devices covering the visible spectral regime from blue
to red emission, while the AlGaN ternary alloy is critical for
application in deep-UV regime. However, the experimental
realization of such material systems has been limited by the
challenges in growing conventional ternary and quaternary alloys
with high indium and aluminum composition.
[0007] In particular, the conventional epitaxy of InGaN alloy with
high In composition results in a phase separated material system,
which leads to detrimental issues in the electronics and
optoelectronic properties of this alloy. The limitation of growing
high quality InGaN alloy with high In content has been one of the
major barriers in the realization of high performance
optoelectronic devices employing indium rich InGaN alloys for
longer wavelength applications. Therefore, new strategies are
necessary to access the epitaxy of high crystalline quality
III-Nitride quaternary and ternary material systems and eventually
achieve the broad tunability of optoelectronic properties in the
III-Nitride platform.
SUMMARY OF INVENTION
[0008] The following presents a simplified summary of the invention
in order to provide a basic understanding of some aspects of the
invention. This summary is not an extensive overview of the
invention. It is not intended to identify key/critical elements of
the invention or to delineate the scope of the invention. Its sole
purpose is to present some concepts of the invention in a
simplified form as a prelude to the more detailed description that
is presented later.
[0009] According to one embodiment, a method of forming a
III-Nitride quaternary digital alloy ("DA") of AlGaInN comprises
generating a periodic structure of closely separated binary alloy
layers, each of said binary alloy layers comprising one of AlN, GaN
and InN, wherein each of said binary alloy layers has a respective
thickness of 1-2 monolayers ("ML"s) and said periodic structure of
binary alloy layers has a total thickness of between 10-50
periods.
[0010] A method of forming a III-Nitride ternary DA comprises
generating a periodic structure of closely separated binary alloy
layers of a first type and a second type, each of said first type
of binary alloy layer comprising one of AlN, GaN and InN and each
of said second type of binary alloy layer comprising one of AlN,
GaN and InN, wherein the first type of binary alloy layer is
different from the second type of binary alloy layer and each of
said binary alloy layers has a respective thickness of 1-4 MLs and
said periodic structure of binary alloy layers has a total
thickness of between 10-50 periods.
[0011] A III-Nitride quaternary DA of AlGaInN comprises a periodic
structure of closely separated binary alloy layers, each of said
binary alloy layers comprising one of AlN, GaN and InN, wherein
each of said binary alloy layers has a respective thickness of 1-2
monolayers ("ML"s) and said periodic structure of binary alloy
layers has a total thickness of between 10-50 periods.
BRIEF DESCRIPTION OF DRAWINGS
[0012] FIG. 1 is a schematic illustration showing how various
ternary and quaternary DAs can be achieved according to one
embodiment.
[0013] FIG. 2A is a schematic illustration of a quaternary
III-Nitride digital alloy achieved by generating a periodic
structure of closely separated binary alloy layers according to one
embodiment.
[0014] FIG. 2B is a schematic illustration of a ternary III-Nitride
digital alloy achieved by generating a periodic structure of two
different closely separated binary alloys according to one
embodiment.
[0015] FIG. 3 illustrates one particular embodiment of a quaternary
AlGaInN DA according to one embodiment.
[0016] FIGS. 4A illustrates a particular embodiments of a ternary
DA of InGaN according to one embodiment.
[0017] FIGS. 4B illustrates a particular embodiments of a ternary
DA of AlGaN according to one embodiment.
[0018] FIGS. 4C illustrates a particular embodiments of a ternary
DA of AlInN according to one embodiment.
[0019] FIG. 5A is a plot illustrating Indium (In)-content in InGaN
DA as a function of thickness of each binary alloy layer
respectively according to one embodiment.
[0020] FIG. 5B is a plot illustrating Aluminum (Al)-content in
AlGaN DA as a function of thickness of each binary alloy layer
respectively according to one embodiment.
[0021] FIG. 6A is a plot illustrating calculated miniband
structures of InGaN DA utilizing 2 ML GaN with 2 ML InN as one
single period element according to one embodiment.
[0022] FIG. 6B is a plot illustrating calculated miniband
structures of InGaN DA utilizing 2 ML GaN with 4 ML InN as one
single period element according to one embodiment.
[0023] FIG. 6C is a plot illustrating calculated miniband
structures of InGaN DA utilizing 4 ML GaN with 2 ML InN as one
single period element according to one embodiment.
[0024] FIG. 6D is a plot illustrating calculated miniband
structures of InGaN DA utilizing 4 ML GaN with 4 ML InN as one
single period element according to one embodiment.
[0025] FIG. 7A is a plot illustrating calculated miniband
structures of AlGaN DA utilizing 2 ML GaN with 2 ML AlN as one
single period element according to one embodiment.
[0026] FIG. 7B is a plot illustrating calculated miniband
structures of AlGaN DA utilizing 4 ML GaN with 2 ML AlN as one
single period element according to one embodiment.
[0027] FIG. 7C is a plot illustrating calculated miniband
structures of AlGaN DA utilizing 2 ML GaN with 4 ML AlN as one
single period element according to one embodiment.
[0028] FIG. 7D is a plot illustrating calculated miniband
structures of AlGaN DA utilizing 4 ML GaN with 4 ML AlN as one
single period element according to one embodiment.
[0029] FIG. 8A shows tunable energy gaps of InGaN DAs formed by M
ML GaN and N ML InN ultra-thin binary-alloy layers according to one
embodiment.
[0030] FIG. 8B shows tunable energy gaps of AlGaN DAs formed by M
ML AlN and N ML GaN ultra-thin binary-alloy layers according to one
embodiment.
[0031] FIG. 9A show calculated wave functions overlap of
ground-state electron and heavy hole as a function of the thickness
of each binary-alloy layer for InGaN DA.
[0032] FIGS. 9B show calculated wave functions overlap of
ground-state electron and heavy hole as a function of the thickness
of each binary-alloy layer for AlGaN DA.
[0033] FIG. 10 illustrates the calculated band edge energy position
of the valence sub-bands (HH and CH bands) in AlGaN DA as a
function of the thickness of each ultra-thin binary alloy
layer.
DETAILED DESCRIPTION
[0034] Applicants have devised a method and system for accessing
all possible ternary and quaternary III-Nitride alloys without the
need for employing high In content and/or high Al content in
III-Nitride structures. According to one embodiment, a set of
artificially engineered nano-structures based on finite
short-period superlattice structures in which different III-Nitride
ultra-thin binary-alloys are utilized to overcome conventional
limitations in growing high quality III-Nitride alloys. To this
end, Applicants have devised a structure, herein referred to as a
III-Nitride Digital Alloy ("DA") comprising a set of artificially
engineered nano-structures, which are based on finite short-period
superlattices formed by closely-separated binary alloy layers.
[0035] According to embodiments described herein, DAs provide an
artificial engineered material structure exhibiting a large
tunability in their respective optoelectronic properties. Based on
the concept of DA, the phase separation issue of conventional
ternary alloys is avoided naturally in this nano-structure through
the alternate epitaxy of high quality binary alloys. Moreover,
employing very thin GaN and InN binary layers introduces strong
inter-well resonant coupling effect within the superlattice
structure and therefore forms miniband structures. Taking advantage
of such resonant coupling effect, miniband engineering can be
performed by carefully designing the DA nano-structure and
controlling the thickness of those binary thin layers during
epitaxy. In this fashion, an effective "digital alloy" can be
achieved with tunable optoelectronic properties comparable to that
of bulk alloy. The thickness of each binary layer in the DA,
represented by a monolayer (ML), determines the tunable
optoelectronic properties of the resultant material. In particular,
according to one embodiment, employing ultra-thin binary layers
with thickness ranging from 1 to 4 MLs introduces a strong
inter-well resonant coupling effect within the superlattice
structure resulting in the formation of miniband structures.
[0036] DAs can be deposited by an epitaxial method employing
alternate growth of ultra thin layers of high crystalline quality
AlN, GaN, and InN binary alloys. By designing the combination of
these binary alloys, a quaternary DA of AlGaInN and a ternary DA of
AlGaN, InGaN, and AlInN can be obtained.
[0037] FIG. 1 is a schematic illustration showing how various
ternary and quaternary DAs can be achieved according to one
embodiment. In particular, the center of the triangle shown in FIG.
1 illustrates generation of a quaternary DA alloy. The sides of the
triangle shown in FIG. 1 illustrate the generation of a ternary DA.
Thus, as shown in FIG. 1 a quaternary alloy of AlGaInN may be
obtained by a periodic structure of closely separated, thin binary
layers of InN, GaN and AlN. A ternary DA of AlInN to be generated
via a periodic structure of closely separated thin binary layers of
AlN and InN. A ternary DA of InGaN may be generated via a periodic
structure of close separated thin binary layers of InN and GaN. A
ternary DA of AlGaN may be generated via a periodic structure of
closely separated thin binary layers of AlN and GaN.
[0038] By performing an alternate epitaxy of high quality
ultra-thin III-Nitride binary alloys, the growth issues of
conventional III-Nitride alloys are naturally avoided using the DA
method described herein. In particular, FIG. 2A is a schematic
illustration of a quaternary III-Nitride digital alloy achieved by
generating a periodic structure of closely separated binary alloy
layers according to one embodiment. As shown in FIG. 2A, a
quaternary DA 110 is achieved by generating a periodic structure
utilizing a periodic element 102, wherein periodic element 102
comprises a group of three different ultra-thin binary-alloy layers
(104, 106 and 108), which are closely-separated from one another.
According to one embodiment, the binary alloy layers comprising
periodic element 102 may be AlN, GaN and InN. By combining all
three ultra-thin binary-alloy layers (e.g. AlN, GaN, and InN) to
form a short-period superlattice, an AlGaInN quaternary DA can be
achieved. Thus, referring to FIG. 2A, a quaternary DA may be
achieved via a periodic structure of P periods of periodic elements
102(1)-102(P), wherein each periodic element comprises three
digital alloys (e.g., 104(1), 106(1) and 108(1)-104(P), 106(P) and
108(P).
[0039] Further, each of the binary alloys (e.g., AlN, GaN and InN)
within a periodic element 102 is associated with a respective
thickness represented in monolayer ("ML") units. Thus, referring
again to FIG. 2A, the AlN binary layers may exhibit a thickness of
L ML, the GaN digital alloy may exhibit a thickness of M ML and the
AlN digital alloy may exhibit a thickness of N ML. By varying the
respective thicknesses of the digital alloys (i.e., M, L and N)
within a periodic element, the optoelectronic properties of the DA
may be tuned.
[0040] Quaternary DA 110 is also associated with a total thickness
T. According to one embodiment, the total thickness T must be
finite and is determined in order to preserve a coherency of a wave
function in quaternary DA 110.
[0041] FIG. 2B is a schematic illustration of a ternary III-Nitride
digital alloy achieved by generating a periodic structure of two
different closely separated binary alloys according to one
embodiment. According to one embodiment, the binary alloy layers
may be two different alloys of AlN, GaN, and InN. In particular,
FIG. 2B is a schematic illustration of a ternary III-Nitride
digital alloy achieved by generating a periodic structure of
closely separated binary alloy layers according to one embodiment.
As shown in FIG. 2B, ternary DA 112 is achieved by generating a
periodic structure utilizing a periodic element 102, wherein
periodic element 102 comprises a group of two different ultra-thin
binary-alloy layers (104, 106), which are closely-separated from
one another. According to one embodiment, the binary alloy layers
comprising periodic element 102 may be any two different ones from
the group of AlN, GaN and InN. Thus, according to one embodiment,
by combining two ultra-thin binary-alloy layers (e.g. two from the
group of AlN, GaN, and InN) to form a short-period superlattice,
either an AlGaN, AlInN or InGaN ternary DA 112 may be achieved.
Thus, referring to FIG. 2B, a ternary DA may be achieved via a
periodic structure of P periods of periodic elements 102(1)-102(P),
wherein each periodic element comprises two digital alloys (e.g.,
104(1), 106(1)-104(P), 106(P)).
[0042] Further, each of the binary alloys (e.g., AlN, GaN and InN)
within a periodic element 102 is associated with a respective
thickness represented in monolayer units. Thus, referring again to
FIG. 2B, the AlN binary layers may exhibit a thickness of L
monolayers, the GaN digital alloy may exhibit a thickness of M ML
and the AlN digital alloy may exhibit a thickness of N ML. By
varying the respective thicknesses of the digital alloys within a
periodic element (i.e., M and L), the optoelectronic properties of
the DA may be tuned.
[0043] Ternary DA 112 is also associated with a total thickness T.
The total thickness T must be finite and is determined according to
one embodiment in order to preserve a coherency of the wave
function in the structure.
[0044] FIG. 3 illustrates one particular embodiment of a quaternary
AlGaInN DA according to one embodiment. Referring to FIG. 3 AlGaInN
DA 302 comprises a periodic structure of periodic elements, wherein
each periodic element comprises three binary digital alloys of AlN,
GaN and InN. As shown in FIG. 3, AlGaInN DA 302 is achieved by
generating a periodic structure utilizing a plurality of periodic
elements 102 (only one specific periodic element 102 is called out
in FIG. 3), wherein periodic element 102 comprises a group of three
different ultra-thin binary-alloy layers of AlN, GaN, and InN,
which are closely-separated from one another.
[0045] As shown in FIG. 3, each periodic element, 102, comprises L
ML layers of InN, M ML of GaN and N ML of AlN. According to one
embodiment, the thicknesses of each layer of InN, GaN and AlN in ML
may be varied to tune the optoelectric properties of quaternary DA
302. That is, the variables L, M, N representing the number of ML
of InN, GaN and AlN may be varied to tune the optoelectrical
properties of AlGaInN DA 302.
[0046] FIGS. 4A-4C illustrate particular embodiments of ternary DAs
of AlGaN, InGaN and AlInN respectively according to one embodiment.
Referring to FIG. 4A InGaN DA 402 comprises a periodic structure of
periodic elements, wherein each periodic element comprises two
binary alloys of InN and GaN. InGaN DA 402 is achieved by
generating a periodic structure utilizing a plurality of periodic
elements 102 (only one specific periodic element 102 is called out
in FIG. 4A), wherein periodic element 102 comprises a group of two
ultra-thin binary-alloy layers of GaN, and InN, which are
closely-separated from one another.
[0047] As shown in FIG. 4A, each periodic element, 102, comprises M
ML layers of GaN and N ML of InN. According to one embodiment, the
thicknesses of each layer of GaN and InN in ML may be varied to
tune the optoelectric properties of ternary DA 402. That is, the
variables M and N representing the number of ML of GaN and InN may
be varied to tune the optoelectrical properties of DA 402.
[0048] According to one embodiment, M and N are varied between 1-4
ML. Further, a total thickness T of 10-50 periods is used.
[0049] Referring to FIG. 4B AlGaN DA 404 comprises a periodic
structure of periodic elements, wherein each periodic element
comprises two binary alloys of AlN and GaN. AlGaN DA 404 is
achieved by generating a periodic structure utilizing a plurality
of periodic elements 102 (only one specific periodic element 102 is
called out in FIG. 4B), wherein periodic element 102 comprises a
group of two ultra-thin binary-alloy layers of AlN, and GaN, which
are closely-separated from one another.
[0050] As shown in FIG. 4B, each periodic element, 102, comprises M
ML layers of GaN and N ML of AlN. According to one embodiment, the
thicknesses of each layer of GaN and AlN in ML may be varied to
tune the optoelectric properties of ternary DA 404. That is, the
variables M and N representing the number of ML of GaN and AlN may
be varied to tune the optoelectrical properties of AlGaN DA
404.
[0051] According to one embodiment, M and N are varied between 1-4
ML. Further, a total thickness T of 10-50 periods is used.
[0052] Referring to FIG. 4C AlInN DA 406 comprises a periodic
structure of periodic elements, wherein each periodic element
comprises two binary alloys of AlN and InN. AlInN DA 406 is
achieved by generating a periodic structure utilizing a plurality
of periodic elements 102 (only one specific periodic element 102 is
called out in FIG. 4C), wherein periodic element 102 comprises a
group of two ultra-thin binary-alloy layers of AlN, and InN, which
are closely-separated from one another.
[0053] As shown in FIG. 4C, each periodic element, 102, comprises M
ML layers of InN and N ML of AlN. According to one embodiment, the
thicknesses of each layer of InN and AlN in ML may be varied to
tune the optoelectric properties of ternary DA 406. That is, the
variables M and N representing the number of ML of InN and AlN may
be varied to tune the optoelectrical properties of DA 406.
[0054] According to one embodiment, M and N are varied between 1-4
ML. Further, a total thickness T of 10-50 periods is used.
[0055] FIGS. 5A-5B illustrate Indium (In)-content in InGaN DA 402
and Aluminum (Al)-content in AlGaN DA 404 as a function of the
thickness of each binary alloy layer respectively. According to one
embodiment, the In-content x in the In.sub.xGa.sub.1-xN DA (and the
Al-content x in the Al.sub.xGa.sub.1-xN) is determined by the duty
cycle x=n/(m+n). Referring to FIGS. 5A-5B, the In-content and
Al-content can both be tuned from 20% to 80% by varying the
thickness of each layer from 1 to 4 MLs in InGaN DA 402 and AlGaN
DA 404.
[0056] FIGS. 6A-6D illustrate calculated miniband structures of
four exemplary InGaN DAs according to one embodiment. In
particular, FIG. 6A shows an InGaN DA 402 utilizing 2 ML GaN with 2
ML InN as one single period element. FIG. 6B shows an InGaN DA 402
utilizing 2 ML GaN with 4 ML InN as one single period element. FIG.
6C shows an InGaN DA 402 utilizing 4 ML GaN with 2 ML InN as one
single period element. FIG. 6D shows an InGaN DA 402 utilizing 4 ML
GaN with 4 ML InN as one single period element.
[0057] FIGS. 6A-6D illustrate that the effective energy gap between
the ground-state miniband in conduction band (C-1) and the
ground-state miniband in valence band (HH-1) is reduced as the
thickness of those InN binary layers increased. Further, as the
thickness of the GaN and InN layers is reduced, the bandwidth of
each miniband increases. These trends suggest that the energy gap
as well as the optoelectronic properties of the DA can be
engineered by simply tuning the thickness of each ultra-thin
binary-alloy layer in the DAs.
[0058] Similar phenomenon can be observed in the AlGaN DA as shown
in FIGS. 7A-7D. In particular, FIGS. 7A-7D illustrate calculated
miniband structures of four exemplary AlGaN DAs according to one
embodiment. In particular, FIG. 7A shows an AlGaN DA 404 utilizing
2 ML GaN with 2 ML AN as one single period element. FIG. 7B shows
an AlGaN DA 404 utilizing 2 ML AN with 4 ML GaN as one single
period element. FIG. 7C shows an AlGaN DA 404 utilizing 4 ML AN
with 2 ML GaN as one single period element. FIG. 7D shows an AlGaN
DA 404 utilizing 4 ML GaN with 4 ML AN as one single period
element.
[0059] FIG. 8A shows tunable energy gaps of InGaN DAs formed by M
ML GaN and N ML InN ultra-thin binary-alloy layers according to one
embodiment. In particular, according to one embodiment, the
effective energy gap of InGaN DAs 402 can be engineered from 0.63
eV (with 1 ML GaN and 4 MLs InN) to 2.4 eV (with 4 MLs GaN and 1 ML
InN). Correspondingly, according to one embodiment, a transition
wavelength of InGaN DA 402 varied between .about.510 nm to
.about.1900 nm covering the green up to infrared regime.
[0060] FIG. 8B shows tunable energy gaps of AlGaN DAs formed by M
ML AlN and N ML GaN ultra-thin binary-alloy layers according to one
embodiment. As shown in FIG. 8B, the tunable energy gap be
engineered from 3.96 eV (with 1 ML AlN and 4 MLs GaN) to 5.20 eV
(with 4 MLs AlN and 1 ML GaN). The corresponding transition
wavelength of AlGaN DA 404 according to this embodiment ranged from
18 240 nm to .about.310 nm covering the deep-UV regime. The broad
tunability of energy gaps covered by InGaN DAs and AlGaN DAs
implies great potential of such III-Nitride DAs as nano-engineered
active regions for optoelectronics applications.
[0061] FIG. 9A show calculated wave function overlap of
ground-state electron and heavy hole as a function of the thickness
of each binary-alloy layer for InGaN DA. As shown in FIG. 9A, the
ground state carrier wavefunction overlap in InGaN DA is varied
from 86% to 99% while the thickness of the GaN and InN binary-alloy
layer changes from 1 to 4 MLs.
[0062] FIG. 9B show calculated wave function overlap of
ground-state electron and heavy hole as a function of the thickness
of each binary-alloy layer for AlGaN DA. As shown in FIG. 9B, the
ground-state carrier wavefunction overlap in the AlGaN DA ranges
from 75% to 97% while the thickness of the AlN and GaN binary-alloy
layer changes from 1 to 4 MLs.
[0063] As shown in FIGS. 9A-9B, for InGaN and AlGaN, the
polarization induced charge separation issue is effectively
suppressed within the III-Nitride DA structures by employing
ultra-thin binary-alloy layers. Eventually, the entire III-Nitride
DA performs as a complete "active alloy" that exhibits comparable
characteristics of a conventional alloy. The large overlaps
observed in these DAs provide a strong suggestion that these
nano-structures behave as an effective "alloy".
[0064] By employing a AlGaN DA structure, the valence band cross
over issue in the conventional AlGaN ternary alloy with high
Al-content can be solved. The valence band cross over issue is
attributed to relocation of the crystal-field spilt-off hole (CH)
band sufficiently higher than the heavy hole (HH) band. Thus the
dominant transition in the conventional AlGaN active region will
switch from C--HH to C--CH leading to a dominant TM-polarized
emission. Such dominant TM-polarized emission is not preferable in
the top emitter application due to its low extraction
efficiency.
[0065] FIG. 10 illustrates the calculated band edge energy position
of the valence sub-bands (HH and CH bands) in AlGaN DA as a
function of the thickness of each ultra-thin binary alloy layer.
Referring to FIG. 10, it is clear to see that the HH band is always
located sufficiently high above the CH band due to the valence band
rearrangement. Such phenomenon indicates that the dominant
transition in the AlGaN DA can be always the C--HH transition
leading to the dominant TE-polarized emission with high efficiency
for the top emitter application.
[0066] These and other advantages maybe realized in accordance with
the specific embodiments described as well as other variations. It
is to be understood that the above description is intended to be
illustrative, and not restrictive. Many other embodiments and
modifications within the spirit and scope of the claims will be
apparent to those of skill in the art upon reviewing the above
description. The scope of the invention should, therefore, be
determined with reference to the appended claims, along with the
full scope of equivalents to which such claims are entitled. In the
appended claims, the terms "including" are used as the
plain-English equivalents of the respective terms "comprising" and
"wherein." Moreover, in the following claims, the terms "first,"
"second," and "third," etc. are used merely as labels, and are not
intended to impose numerical requirements on their objects.
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