U.S. patent application number 13/970732 was filed with the patent office on 2014-07-24 for transparent conductive structure, device comprising the same, and the manufacturing method thereof.
This patent application is currently assigned to EPISTAR CORPORATION. The applicant listed for this patent is EPISTAR CORPORATION. Invention is credited to Yung-Fu Chang, Chong-Long Ho, Ai-Sen Liu, Meng-Chyi Wu.
Application Number | 20140203322 13/970732 |
Document ID | / |
Family ID | 51207054 |
Filed Date | 2014-07-24 |
United States Patent
Application |
20140203322 |
Kind Code |
A1 |
Chang; Yung-Fu ; et
al. |
July 24, 2014 |
Transparent Conductive Structure, Device comprising the same, and
the Manufacturing Method thereof
Abstract
An optical electrical device comprises a base and a transparent
conductive structure on the base is disclosed. The base further
comprises a light-emitting device and the transparent conductive
structure comprises a transparent conductive oxide layer and a
passivation layer on the transparent conductive oxide layer. The
material of the transparent conductive oxide layer comprises
transparent conductive metal oxide, such as ZnO. Furthermore, the
transparent conductive metal oxide also comprises impurities, such
as a carrier e.g. gallium.
Inventors: |
Chang; Yung-Fu; (New Taipei,
TW) ; Wu; Meng-Chyi; (Hsinchu, TW) ; Ho;
Chong-Long; (Taoyuan, TW) ; Liu; Ai-Sen;
(Hsinchu, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EPISTAR CORPORATION |
Hsinchu |
|
TW |
|
|
Assignee: |
EPISTAR CORPORATION
Hsinchu
TW
|
Family ID: |
51207054 |
Appl. No.: |
13/970732 |
Filed: |
August 20, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61755514 |
Jan 23, 2013 |
|
|
|
Current U.S.
Class: |
257/99 |
Current CPC
Class: |
H01L 33/42 20130101;
H01L 31/02963 20130101; H01L 31/1884 20130101; Y02P 70/50 20151101;
H01L 31/1844 20130101; H01L 33/06 20130101; H01L 33/44 20130101;
H01L 31/022483 20130101; Y02P 70/521 20151101; H01L 33/32 20130101;
H01L 2933/0025 20130101; Y02E 10/544 20130101 |
Class at
Publication: |
257/99 |
International
Class: |
H01L 33/62 20060101
H01L033/62 |
Claims
1. An optical electrical device, comprising: a base; a first
transparent conductive layer comprising a first metal oxide having
a first metal element and a fourth metal element on the base; a
second transparent conductive layer comprising a second metal oxide
having a second metal element and a third metal element on the
first transparent conductive layer; and a passivation layer
comprising a dielectric material on the second transparent
conductive layer, wherein the first metal element is different from
the second element.
2. The optical electrical device to claim 1, wherein a mole
fraction of the fourth metal element is greater than that of the
first metal element in the first metal oxide.
3. The optical electrical device to claim 1, wherein a mole
fraction of the second metal element is greater than that of the
third metal element in the second metal oxide.
4. The optical electrical device to claim 1, wherein a mole
fraction of the first metal element in the first metal oxide is
less than 15%.
5. The optical electrical device to claim 1, wherein a valence
state of the first metal element is different from that of the
second metal element.
6. The optical electrical device to claim 1, wherein a valence
state difference between the first metal element and the second
metal element is two.
7. The optical electrical device to claim 6, wherein the first
metal is in group IVA.
8. The optical electrical device to claim 1, wherein the second
metal element and the third metal element belong to groups directly
next to each other in a standard periodic table.
9. The optical electrical device to claim 1, wherein the third
metal element is trivalent.
10. The optical electrical device to claim 1, wherein the third
metal element and the fourth metal element are different elements
of a same group in a standard periodic table.
11. The optical electrical device to claim 10, wherein the same
group is group IIIA.
12. The optical electrical device to claim 1, wherein a mole
fraction of the third metal element in the second metal oxide is
less than 10%.
13. The optical electrical device to claim 1, wherein the
dielectric material comprises aluminum oxide or silicon oxide.
14. The optical electrical device to claim 1, wherein resistivities
of the first transparent conductive layer and the second
transparent conductive layer are both less than 3.3.times.10.sup.-4
.OMEGA.-cm.
15. The optical electrical device to claim 1, wherein the base
comprises a light-emitting semiconductor stack configured to emit
an incoherent light, wherein the light-emitting semiconductor stack
comprises an n-type semiconductor layer, a p-type semiconductor
layer, and an active layer between the n-type semiconductor layer
and the p-type semiconductor layer.
16. The optical electrical device to claim 15, wherein the p-type
semiconductor layer comprises a plurality of hexagonal-pyramid
cavities.
17. The optical electrical device to claim 1, wherein a
transmittance of the second transparent conductive layer is larger
than 95% for a light with a dominant wavelength between 450 nm and
550 nm.
18. The optical electrical device to claim 1, further comprising a
recess formed in the passivation layer.
19. The optical electrical device to claim 18, further comprising
an electrode pad formed in the recess.
20. The optical electrical device to claim 1, wherein a mole
fraction of the first metal element in the first metal oxide is
larger than that of the third metal element in the second metal
oxide.
Description
TECHNICAL FIELD
[0001] This present application relates to a device comprising a
base and a transparent conductive structure on the base and the
method of manufacturing thereof.
BACKGROUND OF THE DISCLOSURE
[0002] An optical electrical device such as light-emitting diode
(LED) of the solid-state lighting elements have the characteristics
of low heat generation, long operational life and the light emitted
by the LEDs has a stable wavelength range so the LEDs have been
widely used in various applications. Efforts have been devoted to
the luminance of the LED in order to apply the device to the
lighting domain and further achieve the goal of energy conservation
and carbon reduction.
[0003] Many improvements on structures or materials to enhance the
light emitting efficiency of an LED have been realized. One of
those improvements is to add an enhanced film to increase light
extraction, optic-electrical transition efficiency, contact
resistance, forward voltage, or the like. However, the high
temperature during manufacturing damages the electrical and/or
light properties of the enhanced film, and induces the resistances
of the enhanced films increasing and the wavelength of maximum
transmittance shifting.
SUMMARY OF THE DISCLOSURE
[0004] An optical electrical device comprises a base and a
transparent conductive structure on the base is disclosed. The base
further comprises a light-emitting device which comprises a first
semiconductor layer, an active layer, and a second semiconductor
layer. The transparent conductive structure comprises a transparent
conductive oxide layer and a passivation layer on the transparent
conductive oxide layer. The transparent conductive structure
prevents carrier out-diffusion from the base. The material of the
passivation layer comprises dielectric material, such as insulating
oxide material comprising aluminum oxide and silicon oxide. The
material of the transparent conductive oxide layer comprises
transparent conductive metal oxide, such as ZnO. Furthermore,
transparent conductive metal oxide also comprises impurities, such
as a carrier e.g. gallium.
[0005] The present disclosure provides a manufacturing method of an
optical electrical device comprises steps of providing a base and
forming a transparent conductive structure on the base. The step of
forming a base further comprises providing a substrate, forming
semiconductor layers on the substrate and growing an active layer
located between the semiconductor layers. The step of forming a
transparent conductive structure further comprises forming a
transparent conductive oxide layer on the base and forming a
passivation layer on the transparent conductive oxide layer.
Moreover, an annealing process is applied after the base and the
transparent conductive structure formed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 shows an embodiment of a device having a transparent
conductive layer in accordance with the present disclosure;
[0007] FIGS. 2(a) and 2(b) depict the resistivity of the
transparent conductive oxide layer with and without the passivation
layer thereon on different base related to the annealing
temperature in various ambient in accordance with the present
disclosure.
[0008] FIGS. 3(a) and 3(b) depict the impurity concentration of the
transparent conductive oxide layer with and without the passivation
layer thereon on different base related to the annealing
temperature in various ambient in accordance with the present
disclosure.
[0009] FIGS. 4(a) and 4(b) depict the mobility of the element doped
in transparent conductive oxide layer with and without the
passivation layer thereon on different base related to the
annealing temperature in various ambient in accordance with the
present disclosure.
[0010] FIGS. 5(a)-5(b) depict the transmittance spectra of the
transparent conductive oxide layer without the passivation layer
thereon;
[0011] FIG. 5(c) depicts the transmittance spectra of the
transparent conductive oxide layer with the passivation layer
thereon related to the wavelength in various ambient in accordance
with the present disclosure.
[0012] FIGS. 6(a)-6(d) show an embodiment of method for forming a
device in accordance with the present disclosure;
[0013] FIG. 7 shows an embodiment in accordance with the present
disclosure.
[0014] FIG. 8 shows an embodiment in accordance with the present
disclosure.
[0015] FIG. 9 shows an embodiment in accordance with the present
disclosure.
DETAILED DESCRIPTION OF THE PRESENT DISCLOSURE
[0016] FIG. 1 shows a device 1 having a transparent conductive
structure 105 in accordance with an embodiment of the present
disclosure. The device 1 comprises a base 100 and a transparenet
conductive structure 105 on the base 100. The transparent
conductive structure 105 comprises a transparent conductive oxide
layer 106 on the base 100 and a passivation layer 108 on the
transparent conductive oxide layer 106. The passivation layer 108
prevents a element doped in the transparent conductive oxide layer
106 from diffusing outside the transparent conductive oxide layer
106 by a thermal annealing process applied to the transparent
conductive structure 105. In other aspect, the passivation layer
108 prevents a doped element from being oxidizied by oxygen and
further decreasing the doping concentration of the doped element.
The doped element is used to increase conductivity of the
transparent conductive oxide layer 106. In other words, part of the
doped element induces carriers, such as electron, to improve
conductivity of the transparent conductive oxide layer 106.
However, the concentration of the doped element is not directly
corresponding to the concentration of the carrier induced by the
doped element. Since one doped element may induce one or more
electrons and not all doped elements induce carriers, the
concentration of the carrier is related to the doping
concentration. The base 100 can be a substrate only or a substrate
having a device structure thereon, wherein the device structure
comprises passive and active components. The passive components
comprises capacitors and resistors. The active components comprises
integrated-circuit structure and photonic-electronic structure
comprising a semiconductor light-emitting structure, a
semiconductor, a solar cell structure, or combination thereof. The
transparent conductive oxide layer 106 comprises metal oxide, such
as zinc oxide(ZnO) doped with group IIIA element, e.g.
aluminum-doped ZnO (AZO), gallium-doped ZnO (GZO), or indium-doped
ZnO (IZO). Furthermore, the mole fraction of the group IIIA element
doped is less than 10% of the transparent conductive oxide layer
106. In an embodiment, the mole fraction of the element doped is
about 5%. In one embodiment, the base 100 comprises a GaN-based
light-emitting structure, and the transparent conductive oxide
layer 106 comprises a ZnO-based semiconducting material having a
band gap (-3.37 eV) wider than that of GaN-based light-emitting
structure and an exciton binding energy (-60 meV) larger than that
of GaN-based light-emitting structure. The electrical property of
the transparent conductive oxide layer 106 is adjustable by
controlling a doping concentration of the element doped in the
transparent conductive oxide layer 106. The passivation layer 108
comprises a dielectric material, such as insulating oxide material,
e.g. aluminum oxide or silicon oxide. The thickness of passivation
layer is about from 50 nm to 300 nm.
[0017] The method for manufacturing the device 1 comprises steps of
providing the base 100, depositing the transparent conductive oxide
layer 106 on the base 100, depositing the passivation layer 108 on
the transparent conductive oxide layer 106, and performing a
thermal annealing process to the device 1 for annealing the
transparent conductive oxide layer 106 in an annealing chamber. The
method for depositing the transparent conductive oxide layer 106
comprises atomic layer deposition (ALD), chemical vapor deposition
(CVD), sol-gel, or spray pyrolysis. The thermal annealing process
comprises rapid thermal annealing (RTA). The method for depositing
the passivation layer 108 comprises e-beam coating. In one
embodiment, the base 100 comprises GaN-based light-emitting
structure, the thermal annealing process is applied to the device 1
for improving the ohmic contact between the interface of the
transparent conductive oxide layer 106 and the GaN-based
light-emitting structure. The light-emitting structure comprises an
n-type semiconductor layer, a p-type semiconductor layer, and a
active layer configured to emit a incoherent light.
[0018] In one embodiment, the transparent conductive oxide layer
106 comprising Ga-doped ZnO is deposited on the base 100 by
thermal-mode ALD with H.sub.2O as an oxidant source. Diethylzinc
(DEZ) and triethylgallium (TEG) are used as the precursors for zinc
and gallium, respectively, while H.sub.2O is used as the precursor
for oxygen or the oxidant source. Argon is used as purge gas and
carrier gas during the deposition. The deposition temperature is
325.degree. C. Precursors are sequentially injected with a pulse
into the reaction chamber with a carrier gas flow of 200 sccm at
the base pressure 0.2 torr. DEZ and H.sub.2O are alternatively
injected into the chamber for ZnO deposition, and the recipe for
the deposition is repeated in cycles. A few cycles of DEZ is
replaced by TEG to dope gallium into ZnO with a ratio of Zn:Ga
around 20:1. The method of injecting the precursors such as DEZ,
TEG, and H.sub.2O having an interval of a pulsetime and a wait
timekept at 0.02 secs and 10 secs. That is, the precursors is
injected following a loop of injecting 0.02 secs and stop for 10
secs. The thickness of ALD-deposited transparent conductive oxide
layer 106 is between 100 nm and 500 nm.
[0019] The thermal annealing process comprising rapid thermal
annealing (RTA) for annealing the transparent conductive oxide
layer 106 is under conditions of an annealing time of 5 minutes, an
annealing temperature range of 300-500.degree. C. for the base 100
being a glass substrate and 400-700.degree. C. for the base 100
being a sapphire substrate. The electrical properties of the
transparent conductive oxide layer 108 are characterized by Hall
method. Transmittance of the transparent conductive oxide layer 108
is measured by using a visible spectrophotometer.
[0020] FIG. 2(a) shows the resistivity of the transparent
conductive oxide layer 106 comprising GZO with and without the
passivation layer 108 thereon on the base 100 which comprises a
glass substrate annealed under various temperature and ambients.
That is, different gases are used as a carrier gas in the annealing
chamber including nitrogen, oxygen, or the mixture of nitrogen and
oxygen with a ratio of 4:1. The transparent conductive oxide layer
106 comprising GZO has a resistivity of 3.9.times.10.sup.-4
.OMEGA.-cm. The thermal annealing process is found deleterious to
the conductivity of the transparent conductive oxide layer 106. The
resistivity of the transparent conductive oxide layer 106 with the
passivation layer 108 thereon and annealed in the oxygen abmient or
the mixture ambient of nitrogen and oxygen is three orders of
magnitude higher than that of the transparent conductive oxide
layer 106 without the passivation layer 108 thereon. This evidence
shows that no matter how much the oxygen content is, the
resistivity of the transparent conductive oxide layer increases
during the thermal annealing process with the oxygen ambient. In
other words, the resistivity of the transparent conductive oxide
layer 106 deposited by ALD is sensitive to oxygen during annealing.
Although the resistivity of the transparent conductive oxide layer
106 deposited on a glass substrate increases over 1000 times after
annealing in an oxygen ambient, the crystallinity of the
transparent conductive oxide layer 106 do not show an obvious
change observed from X-ray diffraction patterns. On the other hand,
it is found that the resistivity of The transparent conductive
oxide layer 106 can be preserved by depositing the passivation
layer 108 onto transparent conductive oxide layer 106. The
transparent conductive oxide layer 106 with the passivation layer
108 thereon has a resistivity lower than that without the
passivation layer 108 thereon after the thermal annealing process.
The resistivity of the transparent conductive oxide layer 106 with
the passivation layer 108 thereon only slightly increases with the
annealing temperature. Meanwhile, the transparent conductive oxide
layer 106 with the SiO.sub.2 passivation layer 108 thereon exhibits
a lower resistivity of 8.2.times.10.sup.-4 .OMEGA.-cm than the
transparent conductive oxide layer 106 with the Al.sub.2O.sub.3
passivation layer of 1.4.times.10.sup.-3 .OMEGA.-cm after annealing
at 500.degree. C. in nitrogen ambient. The transparent conductive
oxide layer 106 covered with the passivation layer 108 thereon can
effectively avoid the increase of resistivity. The resistivity of
the transparent conductive oxide layer 106 increases to
1.85.times.10.sup.-1 .OMEGA.-cm while the carrier gas in the
annealing chamber changes to 80% nitrogen and 20% oxygen filled in
the annealing chamber. The resistivity of the transparent
conductive oxide layer 106 is increased after RTA, especially when
oxygen is added into the annealing chamber as the carrier gas. The
increase of resistivity of the transparent conductive oxide layer
106 also increases the forward operating voltage of a
light-emitting device while using the transparent conductive oxide
layer 106 in a device structure comprising a semiconductor
light-emitting structure. Thus the light emitting efficiency, which
is luminous per watt, is decreased. To sum up, FIG. 2(a) shows the
transparent conductive oxide layer 106 covered by the passivation
layer 108 composed of either silicon oxide or aluminum oxide may
reduce the increase of resistivity of the transparent conductive
oxide layer 106 after RTA.
[0021] FIG. 2(b) shows the resistivity of the transparent
conductive oxide layer 106 comprising GZO with and without the
passivation layer 108 thereon on the base 100 composed of a
sapphire substrate under various temperature and ambients. That is,
different gases are used as a carrier gas in the annealing chamber
including nitrogen and oxygen. The resistivity of the transparent
conductive oxide layer 106 deposited on the sapphire substrate is
3.7.times.10.sup.-4 .OMEGA.-cm, which is lower than that deposited
on the glass substrate. Similar to the trend of the embodiment in
FIG. 2(a), the low resistivity of the transparent conductive oxide
layer 106 deposited on a sapphire substrate with a passivation
layer thereon could be preserved even after RTA. The resistivity
can be reduced to 3.3.times.10.sup.-4 .OMEGA.-cm capped by
SiO.sub.2 passivation layer and reduced to 3.29.times.10.sup.-4
.OMEGA.-cm capped by Al.sub.2O.sub.3 passivation layer after
400.degree. C. RTA. The resistivity still keeps at
6.7.times.10.sup.-4 .OMEGA.-cm for the transparent conductive oxide
layer 106 capped by SiO.sub.2 passivation layer annealed at
700.degree. C. Moreover, it can be observed that the transparent
conductive oxide layer 106 has as low resistivity after the thermal
annealing process as that of the transparent conductive oxide layer
106 before the thermal annealing process. Similar to FIG. 2(a), the
resistivity of the transparent conductive oxide layer 106 formed on
a sapphire substrate is also increased after the thermal annealing
process. In an embodiment, the increase of the resistivity also
increases the forward operating voltage of a light-emitting
device.
[0022] FIG. 3(a) shows the doped concentration of the doped element
in the transparent conductive oxide layer 106 with or without the
passivation layer thereon on the base 100 composed of a glass
substrate under various temperature and ambients. That is,
different gases are used as a carrier gas in the annealing chamber
including nitrogen, oxygen, or the mixture of nitrogen and oxygen
with a ratio of 4:1. FIG. 3(b) show the doped concentration of the
doped element in the transparent conductive oxide layer 106 with or
without the passivation layer thereon on the base 100 composed of a
sapphire substrate under various temperature and ambients. That is,
different gases are used as a carrier gas in the annealing chamber
including nitrogen and oxygen. In an embodiment, the doped element
in the transparent conductive oxide layer 106 induces carrier, thus
the carrier concentration is related to the concentration of the
doped element. The transparent conductive oxide layer 106
comprising GZO has n-type conductivity and an electron
concentration of 10.sup.21 cm.sup.-3 from Hall measurements. As
shown in FIG. 3(a), the doped concentration decays during the RTA,
especially in oxygen ambient. It is attributed to the bonding of
gallium donors in ZnO with oxygen and the bonding of oxygen
vacancies with oxygen. That is the reason the resistivity of GZO is
much sensitive when GZO is annealed in oxygen ambient. When the
transparent conductive oxide layer 106 is annealed in nitrogen
ambient, the doped concentration in the transparent conductive
oxide layer 106 also decays during annealing. It is suggested that
zinc is lost or evaporated during annealing, and causes oxygen
content increasing and vacancy decreasing in the transparent
conductive oxide layer 106. Because of the increase of oxygen
content in the transparent conductive oxide layer 106, the type of
gallium oxide formed in the transparent conductive oxide layer 106
changes from GaO (Ga atoms substitute the Zn sites) to
Ga.sub.2O.sub.3 due to the combination with oxygen. Then the
concentration of doped element, i.e. Ga, for improving conduction
of the transparent conductive oxide layer 106 is reduced, and the
conduction mechanism during annealing in nitrogen ambient is
degraded. As the same trend, the transparent conductive oxide layer
106 with a passivation layer 108 thereon keeps the doped
concentration constant after annealing. It is suggested that the
passivation layer 108 prevents zinc in the GZO from evaporating
during annealing. To be more specific, no matter the transparent
conductive oxide layer 106 is formed on a glass substrate depicted
in FIG. 3(a) or a sapphire substrate depicted in FIG. 3(b), a
passivation layer 108 comprising silicon oxide or aluminum oxide
formed on the transparent conductive oxide layer 106 can reduce the
decrease of the doped concentration of the transparent conductive
oxide layer 106 caused by RTA.
[0023] FIG. 4(a) illustrates the mobility of the doped element in
the transparent conductive oxide layer 106 comprising GZO with and
without the passivation layer deposited on the base 100 composed of
a glass substrate under various temperature and an ambient. That
is, nitrogen is used as a carrier gas in the annealing chamber.
FIG. 4(b) illustrates the mobility of the doped element in the
transparent conductive oxide layer 106 comprising GZO with and
without the passivation layer deposited on the base 100 composed of
a sapphire substrate under various temperature and ambients. That
is, different gases are used as a carrier gas in the annealing
chamber including nitrogen, oxygen, and the mixture of nitrogen and
oxygen with a ratio of 4:1. The doped elements in the transparent
conductive oxide layer 106 induces carriers thus the mobility of
the doped elements indicates the mobility of the carriers in the
transparent conductive oxide layer 106. The transparent conductive
oxide layer 106 comprising GZO has a mobity of about 16
cm.sup.2/V-sec. Reffering to FIGS. 4(a)-4(b), the mobility of GZO
transparent conductive oxide layer 106 deposited on a glass
substrate remains almost the same value by capping the passivation
layer 108 before and after RTA. However, capping SiO.sub.2
passivation layer provides better protection than capping
Al.sub.2O.sub.3 passivation layer. Similar to the case of the
transparent conductive oxide layer 106 deposited on a glass
substrate, the mobility of GZO deposited on the sapphire substrate
is also enhanced with a passivation layer thereon. For the
transparent conductive oxide layer 106 annealed at 700.degree. C.,
the mobility keeps at 17.6 cm.sup.2/V-sec by Al.sub.2O.sub.3
passivation layer, and enhances to 30.2 cm.sup.2/V-sec by SiO.sub.2
passivation layer, as shown in FIG. 4(b). The mobility of the
transparent conductive oxide layer 106 deposited on the sapphire
substrate is higher than that of the transparent conductive oxide
layer 106 deposited on the glass substrate, which is resulted from
the sapphire substrate being crystal-oriented and thus improves the
film quality. To compared with the transparent conductive oxide
layer 106 formed on the base 100 composed of different materials in
FIGS. 4(a) and 4(b), mobilities of the transparent conductive oxide
layer 106 are all decreased after RTA though the amount of the
decrease are different due to the different materials of the base
100. Besides, the passivation layer 108 formed on the transparent
conductive oxide layer 106 in FIGS. 4(a) and 4(b) prevents the
decrease of the mobility of the transparent conductive oxide layer
106 and increases the mobility of the transparent conductive oxide
layer 106 under some circumstances after the thermal annealing
process.
[0024] FIG. 5(a) shows the transmittance spectra of the transparent
conductive oxide layer 106 comprising GZO deposited on the base 100
composed of a glass substrate and annealed at various temperatures
in the nitrogen ambient. As shown in FIG. 5(a), the maximum
transmittance of the transparent conductive oxide layer 106 occurs
at 92.9% at 455 nm and 89% at 710 nm, and the wavelength of the
maximum transmittance shifts toward greater wavelength (i.e.
red-shift) and the intensity increases as the annealing temperature
is increased. The transmittance increases in the longer wavelength
range which is different from the transmittance decreasing in the
longer wavelength range of the transparent conductive oxide layer
106 without passivation formed above. Furthermore, the
transmittance is enhanced in the longer wavelength range after the
thermal annealing process. The transmittance of wavelength at 900
nm raises from 84.4% to 84.9%, 91%, and 96.7% by the annealing
temperature of 300.degree. C., 400.degree. C., and 500.degree. C.,
respectively. As shown in FIG. 5(a), the wavelength spectra of the
transparent conductive oxide layer 106 deposited on the base 100
composed of a glass substrate shifts after 500.degree. C. of RTA
with nitrogen as a carrier gas in the annealing chamber.
[0025] FIG. 5(b) shows the transmittance spectra of the transparent
conductive oxide layer 106 deposited on the base 100 composed of a
glass substrate and annealed at 500.degree. C. in the various
ambients. Similarily, the maximum transmittance shifts to loger
wavelength, i.e. red-shift, while more oxygen flows to the
annealing chamber. This suggests that the maximum transmittance is
dependent on the annealing temperature only, while the wavelength
of maximum transmittance is dependent on the annealing temperature
and the ambient, i.e. the carrier gas in the annealing chamber.
Refferring to FIG. 5(b), the transmittance of the transparent
conductive oxide layer 106 larger than 95% is in a range of
wavelength between 450-550 nm. In comparison with the transmittance
spectra changing of the transparent conductive oxide layer 106
under different RTA conditions, the composition of carrier gas
affects the transmittance spectra and also causes the wavelength
shift. To be more specific, more oxygen added in the carrier gas
induces more wavelength spectra shift of the transparent conductive
oxide layer.
[0026] The wavelength of maximum transmittance in the blue or red
range can be modulated by controlling the thickness of the
passivation layer as an anti-reflective coating layer. FIG. 5(c)
shows the effects of the annealing temperature and ambient gas
during the thermal annealing process on the transmittance spectra
of the transparent conductive oxide layer 106 comprising GZO with
and without the passivation layer 108 deposited on the base 100
composed of a glass substrate. The maximum transmittance of the
transparent conductive oxide layer 106 is 92.9% at wavelength of
455 nm and 89% at 710 nm before annealing. After the thermal
annealing process, the maximum transmittance of the transparent
conductive oxide layer 106 is not only kept in the fixed wavelength
range but also enhanced in the blue and red ranges. The maximum
transmittance of the transparent conductive oxide layer 106 with
the passivation layer 108 is improved to 99.6% at wavelength of 659
nm when capping a Al.sub.2O.sub.3 passivation layer and improved to
99.2% at wavelength of 649 nm when capping a SiO.sub.2 passivation
layer, wherein the improvements are at wavelengths in the red light
range. Besides, the transmittance is improved to 96.2% at 452 nm
when capping a Al.sub.2O.sub.3 passivation layer, and improved to
96.3% at 430 nm when capping a SiO.sub.2 passivation layer, wherein
the improvents are at wavelengths in the blue light range. Addition
of the passivation layer and suitable annealing process
significantly improve both the electrical and optical
characteristics of the transparent conductive oxide layer, which
are beneficial to the applications for optoelectronic devices. To
be more specific, FIG. 5(c) describes the transmittance spectra of
the transparent conductive oxide layer 106 with and without a
passivation layer. FIG. 5(c) shows the increase of the
transmittance while the passivation layer is formed on the
transparent conductive oxide layer 106.
[0027] The disclosure presented above have demonstrated the effects
of the passivation layer and the thermal annealing process on the
transparent conductive oxide layer comprising Ga-doped ZnO grown by
thermal-ALD with using H.sub.2O as oxidant source. The transparent
conductive oxide layer 106 have the resistivity of
3.9.times.10.sup.-4 .OMEGA.-cm grown on a glass substrate and
3.7.times.10.sup.-4 .OMEGA.-cm grown on a sapphire substrate. The
resistivity and transmittance of the transparent conductive oxide
layer 106 increase after the thermal annealing process. The
resistivity of the transparent conductive oxide layer is sensitive
to oxygen during annealing, and increases from 10.sup.-4 to
10.sup.-1 .OMEGA.-cm during the thermal annealing process in the
oxygen ambient. Using aluminium oxide or silicon dioxide as a
passivation layer on the transparent conductive oxide layer 106 is
able to preserve the low resistivity of .about.3.3.times.10.sup.-4
.OMEGA.-cm at a 400.degree. C. RTA process. The maximum
transmittance rises from 92.9% at 455 nm for the transparent
conductive oxide layer to 96.5% at 486 nm at a 500.degree. C. RTA
process in the nitrogen ambient. With the passivation layer, the
maximum transmittance of GZO would improve to .about.99% in red
light range, and .about.96% in blue light range after the thermal
annealing process. Addition of the passivation layer and suitable
annealing process would significantly improve both the electrical
and optical characteristics of the transparent conductive oxide
layer, which are beneficial to the applications for optoelectronic
devices. With the disclosure presented above, the passivation
layers used to preserve the optical and electrical characteristics
of the transparent conductive oxide layer decay after annealing or
even enhance the transmittance and mobility. Since the transparent
conductive oxide layer is used as a light extracting layer, it is
suitable to apply the transparent conductive structure to a
light-emitting device to enhance the optical and electrical
characteristic.
[0028] FIGS. 6(a)-6(d) show an embodiment of a method for forming a
light-emitting device 10 in accordance with one embodiment of the
present disclosure. The method comprises steps of providing a
substrate 102 as shown in FIG. 6(a), epitaxially growing a first
semiconductor layer 1042 of a first conductivity-type on the
substrate 102, epitaxially growing an active layer 1044 having
multi-quantum wells on the first semiconductor layer 1042 for
emitting an incoherent light, and epitaxially growing a second
semiconductor layer 1046 of a second conductivity-type on the
active layer 1044 to form a light-emitting stack 104 as shown in
FIG. 6(b). The first semiconductor layer 1042 and the second
semiconductor layer 1046 has different conductivity types, e.g. the
first semiconductor layer 1042 can be an n-type semiconductor layer
and the second semiconductor layer 1046 can be a p-type
semiconductor layer. A transparent conductive oxide layer 106 is
then deposited on the light-emitting stack 104 and a passivation
layer 108 is then formed on the transparent conductive oxide layer
106 as shown in the FIG. 6(c). The method of manufacturing and the
properties of the transparent conductive oxide layer 106 and the
passivation layer 108 are as the foregoing embodiments from FIG. 1
to FIG. 5(c). The method of forming the transparent conductive
oxide layer 106 comprising providing a metal to form a metal oxide
and providing an element as an impurity for doping. The metal oxide
comprises zinc oxide and the impurity comprises gallium. Moreover,
the step of forming the transparent conductive oxide layer 106
comprises changing the concentration of the gas injected during
forming the transparent conductive oxide layer 106. To be more
specific, injecting the impurity at a first concentration into the
the transparent conductive oxide layer 106 while forming a first
portion of the the transparent conductive oxide layer 106 and
injecting the impurity at a second concentration into the the
transparent conductive oxide layer 106 while forming a second
portion of the the transparent conductive oxide layer 106. Besides,
a concentration ratio between the impurity provided and the metal
of the metal oxide provided to form transparent conductive oxide
layer 106 is larger than 3%. To be more specific, the ratio is
between 5%-20%.
[0029] Referring to the FIG. 6(d), a recess 114 is formed in the
passivation layer 108 to expose a part of the transparent
conductive oxide layer 106, and a first electrode pad 110 is then
formed on the exposed transparent conductive oxide layer 106. A
second electrode pad 112 is formed on a side of the substrate 102
oppossing to the light-emitting stack 104. A thermal annealing
process is performed on the light-emitting device 10, and a
vertical-type light-emitting device as shown in FIG. 6(d) is
formed. In another embodiment, the thermal annealing process is
performed after the passivation layer 108 is formed and before
forming the electrode pad is formed. The detail of the thermal
annealing process are disclosed as the foregoing embodiments from
FIG. 1 to FIG. 5(c). FIG. 7 shows a horizontal-type light-emitting
device 11 in accordance with an embodiment of this application. The
light-emitting stack 104 is etched to exposed a part of the first
semiconductor layer 1042, and the second electrode pad 112 is
formed on the exposed part of the first semiconductor layer
1042.
[0030] In another embodiment, a transparent conductive layer is
adopted to enhance the conductivity. Referring to FIG. 8, the light
emitting device 20 comprises a first semiconductor layer 2042 of a
first conductivity-type on the substrate 202, an active layer 2044
on the first semiconductor layer 2042 for emitting an incoherent
light, and a second semiconductor layer 2046 of a second
conductivity-type on the active layer 2044 to form a light-emitting
stack 204. The first semiconductor layer 2042 and the second
semiconductor layer 2046 has different conductivity type, e.g. the
first semiconductor layer 2042 can be an n-type semiconductor layer
and the second semiconductor layer 2046 can be a p-type
semiconductor layer. The transparent conductive layer 205 is formed
on the second semiconductor layer 2046 and the material of the
transparent conductive layer 205 comprises indium tin oxide (ITO).
The ITO used in the transparent conductive layer 205 compriss a tin
of tetravalent state and an indium of trivalent state, and the mole
fraction of the tin is less than 15%. In another embodiment, the
mole fraction of tin in ITO is between 1%-10%. The two metal
elements used in the transparent conductive layer 205 are of
different valence state. To be more specific, tin is an element of
the group IVA and indium is an element of group IIIA wherein the
two different groups are next to each other. A transparent
conductive oxide layer 206 is formed on the transparent conductive
layer 205 and a passivation layer 208 is formed on the transparent
conductive oxide layer 206. In this embodiment, the material of the
transparent conductive oxide layer 206 comprises GZO. The GZO used
in the transparent conductive oxide layer 206 comprises a zinc of
bivalent state and a gallium of trivalent state, and the mole
fraction of the gallium is less than 10%. In an embodiment, the
concentration of the gallium can be 1%-5%. The two metal elements
used in the transparent conductive oxide layer 206 are of different
valence state. To be more specific, zinc is an element of the group
IIB and gallium is an element of group IIIA wherein the two
different groups are next to each other. In comparison with the
transparent conductive layer 205 and the transparent conductive
oxide layer 206, the two layers comprise metal elements of a group
(indium of the transparent conductive layer 205 and gallium of the
transparent conductive oxide layer 206) and metal elements have
different valence state (tin of tetravalent state in the
transparent conductive layer 205 and zinc of bivalent state in the
transparent conductive oxide layer 206). A recess 214 is formed in
the passivation layer 208 to expose a part of the transparent
conductive oxide layer 206, and a first electrode pad 210 is then
formed on the exposed transparent conductive oxide layer 206. A
second electrode 212 is formed on a side of the substrate 202
opposing to the light-emitting stack 204.
[0031] Referring to FIG. 9, a horizontal-type light-emitting device
21 in accordance with one embodiment of the present disclosure
comprises a substrate 202, a light-emitting stack 204, a
transparent conductive layer 205, a transparent conductive oxide
layer 206, a passivation layer 208, a first electrode pad 210 and a
second electrode pad 212. The light-emitting stack 204 comprises a
first semiconductor layer 2042, an active layer 2044, and a second
semiconductor layer 2046. In this embodiment, the light-emitting
stack 204 is etched to expose a part of the first semiconductor
layer 2042 wherein the second electrode pad 212 is formed on the
exposed part of the first semiconductor layer 2042. Moreover, the
second semiconductor layer 2046 is etched to form a plurality of
hexagonal-pyramid cavities 2052. Thus, convexs and concaves are
formed on the top surface 2051 of the second semiconductor layer
2046. Besides, the hexagonal-pyramid cavities 2052 are extended
downward from the top surface 2051 so each of the transparent
conductive layer 205 formed on the second semiconductor layer 2046
and the transparent conductive oxide layer 206 formed on the
transparent conductive layer 205 has a concave-convex surface. A
recess 214 is formed in the passivation layer 108 to expose a part
of the transparent conductive oxide layer 206, and a first
electrode pad 210 is then formed on the exposed part of the
transparent conductive oxide layer 206.
[0032] It will be apparent to those having ordinary skill in the
art that various modifications and variations can be made to the
devices in accordance with the present disclosure without departing
from the scope or spirit of the disclosure. In view of the
foregoing, it is intended that the present disclosure covers
modifications and variations of this disclosure provided they fall
within the scope of the following claims and their equivalents.
* * * * *