U.S. patent application number 14/171696 was filed with the patent office on 2015-01-08 for vertically structured led by integrating nitride semiconductors with zn(mg,cd,be)o(s,se) and method for making same.
This patent application is currently assigned to ZN Technology, Inc.. The applicant listed for this patent is ZN Technology, Inc.. Invention is credited to Jin Joo Song, Jizhi Zhang.
Application Number | 20150008461 14/171696 |
Document ID | / |
Family ID | 42677442 |
Filed Date | 2015-01-08 |
United States Patent
Application |
20150008461 |
Kind Code |
A1 |
Zhang; Jizhi ; et
al. |
January 8, 2015 |
VERTICALLY STRUCTURED LED BY INTEGRATING NITRIDE SEMICONDUCTORS
WITH Zn(Mg,Cd,Be)O(S,Se) AND METHOD FOR MAKING SAME
Abstract
A light emitting diode (LED) with a vertical structure,
including electrical contacts on opposing sides, provides increased
brightness. In some embodiments an LED includes a nitride
semiconductor light emitting component grown on a sapphire
substrate, a Zn(Mg,Cd,Be)O(S,Se) assembly formed on the nitride
semiconductor component, and a further Zn(Mg,Cd,Be)O(S,Se) assembly
bonded on an opposing side of the light emitting component, which
is exposed by removing the sapphire substrate. Electrical contacts
may be connected to the Zn(Mg,Cd,Be)O(S,Se) assembly and the
further Zn(Mg,Cd,Be)O(S,Se) assembly. Herein Zn(Mg,Cd,Be)O(S,Se) is
a II-VI semiconductor satisfying a formula
Zn.sub.1-a-b-cMg.sub.aCd.sub.bBe.sub.cO.sub.1-p-qS.sub.pSe.sub.q,
wherein a=0.about.1, b=0.about.1, c=0.about.1, p=0.about.1, and
q=0.about.1.
Inventors: |
Zhang; Jizhi; (Brea, CA)
; Song; Jin Joo; (Brea, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ZN Technology, Inc. |
Brea |
CA |
US |
|
|
Assignee: |
ZN Technology, Inc.
Brea
CA
|
Family ID: |
42677442 |
Appl. No.: |
14/171696 |
Filed: |
February 3, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12397224 |
Mar 3, 2009 |
8642369 |
|
|
14171696 |
|
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Current U.S.
Class: |
257/94 |
Current CPC
Class: |
H01L 21/0242 20130101;
H01L 21/02554 20130101; H01L 33/40 20130101; H01L 33/08 20130101;
H01L 33/32 20130101; H01L 33/46 20130101; H01L 21/02565 20130101;
H01L 33/26 20130101; H01L 21/0256 20130101; H01L 33/0093 20200501;
H01L 33/504 20130101; H01L 21/02557 20130101; H01L 21/02568
20130101; H01L 33/0025 20130101 |
Class at
Publication: |
257/94 |
International
Class: |
H01L 33/00 20060101
H01L033/00; H01L 33/50 20060101 H01L033/50; H01L 33/46 20060101
H01L033/46 |
Claims
1. A light emitting diode (LED), comprising: a nitride
semiconductor light emitting component containing at least a p-type
nitride semiconductor and an n-type nitride semiconductor, the
nitride semiconductor light emitting component having a positive
side and a negative side; a conductive Zn(Mg,Cd,Be)O(S,Se) assembly
attached to the positive side of the nitride semiconductor light
emitting component; a positive electrode coupled to the conductive
Zn(Mg,Cd,Be)O(S,Se) assembly; and a negative electrode coupled to
the negative side of the nitride semiconductor light emitting
component.
2. The LED of claim 1, further comprising a further conductive
Zn(Mg,Cd,Be)O(S,Se) assembly attached to the negative side of the
nitride semiconductor light emitting component, with the negative
electrode coupled to the negative side of the nitride semiconductor
light emitting component by way of the further conductive
Zn(Mg,Cd,Be)O(S,Se) assembly.
3. The LED of claim 1, wherein said Zn(Mg,Cd,Be)O(S,Se) represents
any of the group II-VI semiconductors satisfying a formula
Zn.sub.1-a-b-cMg.sub.aCd.sub.bBe.sub.cO.sub.1-p-qS.sub.pSe.sub.q,
wherein a=0.about.1, b=0.about.1, c=0.about.1, p=0.about.1, and
q=0.about.1.
4. The LED of claim 1, wherein the nitride semiconductor light
emitting component comprises: an n-type nitride semiconductor; a
nitride active region on the n-type nitride semiconductor; and a
p-type nitride semiconductor on the nitride active region.
5. The LED of claim 1, wherein the nitride semiconductors satisfy
the formula Al.sub.xGa.sub.yIn.sub.1-x-yN, inclusive of x=0, y=0,
and x=y=0.
6. The LED of claim 1, wherein said nitride semiconductor light
emitting component is configured to emit infrared, red, yellow,
green, blue, violet, or ultraviolet portion of the electromagnetic
spectrum.
7. The LED of claim 1, wherein the conductive Zn(Mg,Cd,Be)O(S,Se)
assembly comprises at least one conductive Zn(Mg,Cd,Be)O(S,Se)
layer.
8. The LED of claim 7, wherein the conductive Zn(Mg,Cd,Be)O(S,Se)
layer is doped with one or several elements from a group including
Ga, Al, In, B, Tl, Zn, Cu, Ag, Au, C, Si, Ge, N, P, As, Sb, Pb, F,
Cl, Br, and I.
9. The LED of claim 1, wherein at least one of the conductive
Zn(Mg,Cd,Be)O(S,Se) assembly and the further conductive
Zn(Mg,Cd,Be)O(S,Se) assembly includes Zn(Mg,Cd,Be)O(S,Se)-hosted
phosphors for color conversion or blending.
10. The LED of claim 9, wherein the Zn(Mg,Cd,Be)O(S,Se)-hosted
phosphors include at least one of transition metals or rare earth
ions in the periodic table of elements.
11. The LED of claim 1, wherein at least one surface or layer
interface is a roughened surface or layer interface for light
extraction enhancement.
12. The LED of claim 2, wherein the further conductive
Zn(Mg,Cd,Be)O(S,Se) assembly contains at least a
Zn(Mg,Cd,Be)O(S,Se) layer.
13. The LED of claim 1, wherein one of the electrodes is used as a
light reflector.
14.-23. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to light emitting
diodes (LEDs) and more particularly to LEDs comprised of a nitride
semiconductor light emitting component and a conductive group II-V
semiconductor, preferably satisfying a formula
Zn.sub.1-a-b-cMg.sub.aCd.sub.bBe.sub.cO.sub.1-p-qS.sub.pSe.sub.q,
wherein a=0.about.1, b=0.about.1, c=0.about.1, p=0.about.1, and
q=0.about.1.
[0002] Most LED structures composed of group III nitride
semiconductors are grown on sapphire substrates. The drawback of
sapphire in this application is that it is electrically an
insulator. As a result, a positive electrode 100 and a negative
electrode 500 of an LED structure can not sandwich a light-emitting
component 300 and have to be made on the same side of a sapphire
substrate 401, as typically shown in FIG. 2, which is known as
lateral injection structure.
[0003] LEDs of the said lateral injection structure are known to
have low wall-plug efficiency, which results from three major
facts. First, the effective current injection area or a light
emitting area 310 is restricted by the area of the positive
electrode 100. In the lateral injection structure, the positive
electrode 100, having poor transparency, can only be fabricated to
cover a small portion of a p-type nitride semiconductor 301, or
most of the light will not be extracted. Because the p-type nitride
semiconductor 301 is a poor semiconductor, significantly less
conductive than an n-type nitride semiconductor 303, the injected
current can not be effectively spread laterally and the current
injection is only restricted under the positive electrode 100.
Second, a significant amount of output light is blocked by the
electrode 100. Third, LEDs of the lateral injection structure have
an additional series resistance, caused by a current crowding
effect in a thin n-type nitride semiconductor 303 as the electrical
current passes by laterally. This inevitably results in a
significant reduction of light emission efficiency due to thermal
effects.
[0004] If a highly conductive, transparent material replaces the
insulative sapphire substrate 401 and another highly conductive,
transparent material is attached onto the top of the less
conductive, p-type layer 301, then a vertically structured LED is
generally formed as shown in FIG. 3 (although, it should be
emphasized, not as later specifically discussed with respect to
FIG. 3). Compared to the said lateral injection structure, the
vertically structured LED has an enlarged effective current
injection area or light emitting area 310 and an enhanced ratio of
the output light to the light blocked by the positive electrode
100. Also there is no more considerable said additional series
resistance associated with the lateral transport in the n-type
nitride semiconductor 303. Therefore, the vertically structured LED
has a significantly improved wall plug efficiency. The effective
current injection area or light emitting area 310 herein has the
same normal as that of the sapphire substrate surface.
[0005] Theoretically, GaN could be an ideal substrate to replace
the insulator, sapphire substrate 401 for the said vertical LED
structure. However, high crystalline, high conductive GaN
substrates are not available with low cost. Moreover, homoepitaxy
growth of nitride LED structure on GaN substrates has so far been
considered very challenging.
[0006] SiC substrate has been used as a conductive substrate for
the said vertical LED structure. Yet, the bulk growth of SiC is
very difficult since the melting point of hexagonal SiC is over
3000.degree. C. and, consequently, SiC substrates are expensive.
There are also significantly large a and c axis lattice parameter
mismatches between SiC and GaN, 3.6% and 94%, respectively.
[0007] Silicon could also be another alternative conductive
substrate for vertical LED. However, it is a narrow bandgap
semiconductor and known to significantly absorb ultraviolet,
violet, blue, green, yellow, red, and near infrared light.
Therefore nitride LEDs formed on silicon substrates have low
efficiency.
SUMMARY OF THE INVENTION
[0008] This invention provides a vertically structured LED. In some
aspects the invention provides an LED with improved brightness and
reliability by integrating a light-emitting component made from
nitride semiconductors satisfying a formula
Al.sub.xGa.sub.yIn.sub.1-x-yN, inclusive of x=0, y=0, and x=y=0
with a conductive group II-VI semiconductor satisfying a formula
Zn.sub.1-a-b-cMg.sub.aCd.sub.bBe.sub.cO.sub.1-p-qS.sub.pSe.sub.q,
wherein a=0.about.1, b=0.about.1, c=0.about.1, p=0.about.1, and
q=0.about.1. Hereafter, Zn(Mg,Cd,Be)O(S,Se) is used to denote any
of the said group II-VI semiconductor family satisfying the formula
Zn.sub.1-a-b-cMg.sub.aCd.sub.bBe.sub.cO.sub.1-p-qS.sub.pSe.sub.q,
wherein a=0.about.1, b=0.about.1, c=0.about.1, p=0.about.1, and
q=0.about.1. In particular, the flow pattern of electrical current
in the said LED is improved by employing at least one conductive
Zn(Mg,Cd,Be)O(S,Se) assembly composed of at least one highly
conductive Zn(Mg,Cd,Be)O(S,Se) layer attached to the said
light-emitting component. The said conductive Zn(Mg,Cd,Be)O(S,Se)
assembly may contain several Zn(Mg,Cd,Be)O(S,Se) layers or bulks of
various shapes.
[0009] A first manufacturing method is provided for forming a first
vertically structured LED that includes two conductive
Zn(Mg,Cd,Be)O(S,Se) assemblies, generally comprising:
[0010] Forming a light-emitting component made from nitride
semiconductors satisfying the formula
Al.sub.xGa.sub.yIn.sub.1-x-yN, inclusive of x=0, y=0, and x=y=0
preferably on a sacrificial substrate that is to be removed. The
sacrificial substrate is preferably sapphire or silicon, but could
be some other type of substrate. In some embodiments, a thin buffer
layer is preferably formed on the sacrificial substrate prior to
forming the light-emitting component. The light-emitting component
includes an n-type nitride semiconductor, a nitride active region
composed of one quantum well (QW) or multiple QWs, and a p-type
nitride semiconductor, which are subsequently formed on the said
thin buffer layer. It may also include an n.sup.+ nitride layer
formed on the said p-type nitride semiconductor. Additionally, the
light-emitting component has polarity because it contains a p-n
junction;
[0011] Forming a first conductive Zn(Mg,Cd,Be)O(S,Se) assembly that
has an n.sup.+ Zn(Mg,Cd,Be)O(S,Se) layer attached onto the nitride
semiconductor side (not the side on the said substrate) of the
light-emitting component, wherein the said nitride semiconductor
side is the positive side of the light-emitting component;
[0012] Removing the said sacrificial substrate and the said thin
buffer layer. If a sapphire substrate is employed as the
sacrificial substrate, then the sapphire substrate could be removed
using, for example, a laser lift-off (LLO) process. With the LLO
process for the sapphire substrate removal, the thin buffer layer
is generally damaged during the laser lift-off process, therefore,
the said n-type nitride semiconductor is exposed. In another
aspect, if a silicon substrate is used as the sacrificial
substrate, then the silicon wafer can be removed using, for
example, selective wet etching, or a combination of mechanical
lapping and selective wet etching. This is followed by a short time
dry etching to remove the said thin buffer layer so that the said
n-type nitride semiconductor can be exposed. For the sacrificial
substrate removal, other methods may also be used, depending on the
specific sacrificial substrate used;
[0013] Forming the second conductive Zn(Mg,Cd,Be)O(S,Se) assembly
on the exposed side of the n-type nitride semiconductor after the
sacrificial substrate removal. The exposed side of the n-type
nitride semiconductor herein is the negative side of the
light-emitting component; and
[0014] Forming the positive and the negative electrodes attached to
the first conductive Zn(Mg,Cd,Be)O(S,Se) and the second conductive
Zn(Mg,Cd,Be)O(S,Se) assemblies, respectively. In some embodiments,
one of the electrodes is made as a light reflector so that light
extraction can be enhanced.
[0015] A second manufacturing method is provided for forming a
second vertically structured LED of this invention, including one
conductive Zn(Mg,Cd,Be)O(S,Se) assembly (namely, still called as
the first conductive Zn(Mg,Cd,Be)O(S,Se) assembly). This method
generally comprises:
[0016] Forming a light-emitting component made from nitride
semiconductors satisfying the formula
Al.sub.xGa.sub.yIn.sub.1-x-yN, inclusive of x=0, y=0, and x=y=0 on
a sacrificial substrate. The sacrificial substrate is preferably to
be sapphire or silicon, but could be else. In some embodiments, a
thin buffer layer is preferably formed on the sacrificial substrate
prior to forming the said light-emitting component. The said
light-emitting component includes an n-type nitride semiconductor,
a nitride active region composed of one quantum well (QW) or
multiple QWs, and a p-type nitride semiconductor, which are
subsequently formed on the said thin buffer layer. It may also
include an n.sup.+ nitride layer formed on the said p-type nitride
semiconductor;
[0017] Forming the first conductive Zn(Mg,Cd,Be)O(S,Se) assembly
that has an n.sup.+ Zn(Mg,Cd,Be)O(S,Se) layer attached onto the
nitride semiconductor side (not the substrate side) of the
light-emitting component, wherein the said nitride semiconductor
side is the positive side of the light-emitting component;
[0018] Removing the sacrificial substrate and the said thin buffer
layer to expose the n-type nitride semiconductor; and
[0019] Forming the positive electrode attached to the first
conductive Zn(Mg,Cd,Be)O(S,Se) assembly and the negative electrode
attached to the exposed side of the n-type nitride semiconductor.
The said exposed side of the n-type nitride semiconductor herein is
the negative side of the light-emitting component. One of the two
electrodes is made as a light reflector so that light extraction
can be enhanced.
[0020] The said Zn(Mg,Cd)O(S,Se) assemblies of this invention may
contain at least a layer or a portion that is doped with phosphors.
After absorption of the original light emitted from the said
nitride active region, the phosphors remit lights of their own
characteristic colors. The overall effect to an observer or a
detector is that the color of the said original light is converted
or blended. By choosing the proper phosphor type or types and
controlling the corresponding amounts, the LED of this invention is
capable of emitting light of various colors, such as infrared, red,
yellow, green, blue, violet, and ultraviolet portions of the
electromagnetic spectrum. Herein Zn(Mg,Cd,Be)O(S,Se) is used as the
phosphor host. The said phosphors are typically composed of at
least one of the transition metals or rare earth ions of various
types.
[0021] In another aspect, the vertically structured LED of this
invention may employ at least one light scattering medium for LED
brightness enhancement. The said light scattering medium or media
may be used to reduce light trapped in the LED structure due to
total internal reflection so that external quantum efficiency can
be significantly improved. This may be implemented by roughening
the interface between the first Zn(Mg,Cd,Be)O(S,Se) assembly 200
and the light-emitting component 300. This can also be implemented
by roughening any surface of any Zn(Mg,Cd,Be)O(S,Se) and nitride
layers of the said vertically structured LED. The roughening
methods could be wet chemical etching, dry etching, growth
parameter control, or other methods.
[0022] In another aspect the invention provides a light emitting
diode (LED), comprising a nitride semiconductor light emitting
component containing at least a p-type nitride semiconductor and an
n-type nitride semiconductor, the nitride semiconductor light
emitting component having a positive side and a negative side; a
conductive Zn(Mg,Cd,Be)O(S,Se) assembly attached to the positive
side of the nitride semiconductor light emitting component; a
positive electrode coupled to the conductive Zn(Mg,Cd,Be)O(S,Se)
assembly; and a negative electrode coupled to the negative side of
the nitride semiconductor light emitting component.
[0023] Yet, in another aspect the invention provides a method of
forming a light emitting diode (LED), comprising limning a
light-emitting component made from nitride semiconductors
satisfying the formula Al.sub.xGa.sub.yIn.sub.1-x-yN, inclusive of
x=0, y=0, and x=y=0, on a sacrificial substrate; forming a
conductive Zn(Mg,Cd,Be)O(S,Se) assembly that has a n+
Zn(Mg,Cd,Be)O(S,Se) layer on the light emitting component; removing
the sacrificial substrate and a thin buffer layer thereon to expose
a negative side of the light emitting component; forming a positive
electrode coupled to the conductive Zn(Mg,Cd,Be)O(S,Se) assembly;
and forming a negative electrode coupled to the negative side of
the light emitting component.
[0024] Other systems, methods, features and advantages of the
invention will be or become apparent to one with skill in the art
upon examination of this disclosure, including the figures and
detailed description. It is intended that all such additional
systems, methods, features and advantages be included within this
description, be within the scope of aspects of the invention, and
the novel and unobvious aspects be protected by the accompanying
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Aspects of the invention can be better understood with
reference to the accompanying figures. The components in the
figures are not necessarily to scale, with emphasis instead being
placed upon illustrating the principles of aspects of the
invention. In the figures, like reference numerals designate
corresponding parts throughout the different views.
[0026] FIG. 1 is a cross-sectional diagram of a vertically
structured LED according to the present invention.
[0027] FIG. 2 is a cross-sectional diagram of an LED structure
grown on a sapphire substrate, showing the localized current
injection pattern.
[0028] FIG. 3 is a cross-sectional diagram of an LED integrated
with conductive Zn(Mg,Cd,Be)O(S,Se) assemblies, showing
significantly enlarged current injection pattern.
[0029] FIG. 4a is a schematic drawing showing the optical
phenomenon of total internal reflection; FIG. 4b is a schematic
drawing showing how light extraction is enhanced with a roughened
interface.
[0030] FIG. 5 shows a flow chart illustrating how a vertically
structured LED integrated with two conductive Zn(Mg,Cd,Be)O(S,Se)
assemblies is formed.
[0031] FIGS. 6a and 6b illustrate cross-sectional views of two
vertically structured LED styles according to a first embodiment of
this invention, with 6a for a bottom emission style and 6b for a
top emission style, respectively.
[0032] FIG. 7 shows a flow chart illustrating how the vertically
structured LED integrated with one conductive Zn(Mg,Cd,Be)O(S,Se)
assembly is formed.
[0033] FIGS. 8a and 8b illustrate cross-sectional views of two
vertically structured LED styles according to a second embodiment
of this invention, with 8a for a bottom emission style and 8b for a
top emission style, respectively.
[0034] FIG. 9 is a comparative plot of the light output power of
diodes according to the present invention and those of reference
diodes drawn as functions of input electrical power.
[0035] FIG. 10 is a plot of emission wavelength deviation versus
light output power for diodes according to the present invention,
in contrast to those of reference diodes.
DETAILED DESCRIPTION
[0036] The present invention provides a vertically structured LED
that integrates a nitride semiconductor light emitting component
with at least one conductive Zn(Mg,Cd,Be)O(S,Se) assembly. The
nitride semiconductor light emitting component is integrated with
the conductive Zn(Mg,Cd,Be)O(S,Se) assembly or Zn(Mg,Cd,Be)O(S,Se)
assemblies such that the effective current injection area or light
emitting area 310 is significantly enhanced. In the vertically
structured LED, a portion of the said conductive
Zn(Mg,Cd,Be)O(S,Se) assembly or Zn(Mg,Cd,Be)O(S,Se) assemblies may
be doped with at least one of the transition metals or rare earth
ions of various types as a phosphor host, therefore the present
invention is also a vertical injection apparatus capable of
emitting high brightness light with colors of white, ultraviolet,
violet, blue, green, yellow, red, and infrared.
[0037] FIG. 1 shows an embodiment of structure in accordance with
aspects of the invention. The structure is composed of a positive
electrode 100, a first conductive Zn(Mg,Cd,Be)O(S,Se) assembly 200,
a nitride semiconductor light emitting component 300, a second
conductive Zn(Mg,Cd,Be)O(S,Se) assembly 400, and a negative
electrode 500. In some embodiments the first conductive
Zn(Mg,Cd,Be)O(S,Se) assembly comprises ZnO, or some other member of
the Zn(Mg,Cd,Be)O(S,Se) family. Similarly, in some embodiments the
second conductive Zn(Mg,Cd,Be)O(S,Se) assembly comprises ZnO, or
some other member of the Zn(Mg,Cd,Be)O(S,Se) family. As shown in
FIG. 1, the first conductive Zn(Mg,Cd)O(S,Se) assembly and the
second conductive Zn(Mg,Cd)O(S,Se) assembly sandwich the nitride
semiconductor light emitting component. The positive electrode is
coupled to the first conductive Zn(Mg,Cd,Be)O(S,Se) assembly, on a
side opposite the nitride semiconductor light emitting component.
Similarly, the negative electrode is coupled to the second
conductive Zn(Mg,Cd)O(S,Se) assembly, also on a side opposite the
nitride semiconductor light emitting component. Other structures
will become apparent to one with skill in the art upon
understanding the spirit of various aspects of the invention.
[0038] The II-VI semiconductor family Zn(Mg,Cd,Be)O(S,Se) is a
material that may be used for fabrication of a vertically
structured LED with the insulator, sapphire substrate 401 removed.
Among the said II-VI semiconductor family, ZnO is a typical
representative. ZnO is a wide bandgap semiconductor, transparent
with respect to visible light, and can be conductive when doped
with certain elements. In contrast to SiC, ZnO has several
advantages, including but not limited to the following. First, bulk
growth of ZnO is relatively easy as the melting point of ZnO is
significantly lower (1975.degree. C.), therefore, the cost of a ZnO
wafer is believed much lower as the market grows. Second, the a and
c lattice parameter mismatches between ZnO and GaN are very low
(1.9% and 0.5%, respectively) and are much less than those between
SiC and GaN. This could potentially lead to significant improvement
of the reliability of the said nitride LEDs. Third, ZnO has a wider
bandgap than SiC resulting in a wider transparent range in the
light spectrum. Furthermore, highly conductive ZnO films can be
easily achieved. For example, highly conductive ZnO films for this
invention have been successfully grown with resistivities as low as
2.5.times.10.sup.-4 .OMEGA.cm.
[0039] In another aspect, single-phase Zn.sub.1-aMg.sub.aO,
Zn.sub.1-bCd.sub.bO, and Zn.sub.1-cBe.sub.cO ternaries of various
compositions have been successfully achieved with crystallographic
structures similar to that of GaN. In particular, the a-axis
lattice mismatches of Zn.sub.1-aMg.sub.aO and Zn.sub.1-bCd.sub.bO,
with compositions a<33% and b<7% have been measured less than
0.4% with respect to GaN (See, "Band gap engineering based on
Mg.sub.xZn.sub.1-xO and Cd.sub.yZn.sub.1-yO ternary alloy films",
T. Makino, Y. Segawa, M. Kawasaki, A. Ohtomo, R. Shiroki, K.
Tamura, and T. Yasuda, Appl. Phys. Lett. 78, (2001) 1237,
incorporated by reference herein). Other ternaries
Zn.sub.1-cBe.sub.cO, ZnO.sub.1-pS.sub.p, ZnO.sub.1-qSe.sub.q, etc.,
may also have crystallographic structures similar to GaN.
Therefore, the Zn(Mg,Cd,Be)O(S,Se) family, for example ZnO,
Zn.sub.1-aMg.sub.aO, Zn.sub.1-bCd.sub.bO, Zn.sub.1-cBe.sub.cO,
ZnO.sub.1-pS.sub.p, and ZnO.sub.1-qSe.sub.q can also be used to
form the vertical LED, in addition to, for example, ZnO.
[0040] Unlike sapphire and SiC for which etching is very difficult,
most Zn(Mg,Cd,Be)O(S,Se) materials are amenable to etching,
especially wet chemical etching--a process that could lead to lower
manufacture cost. Patterns of various shapes can be formed on most
Zn(Mg,Cd,Be)O(S,Se) films or wafers by wet etching using various
acids, some bases, and even some salt solutions with low cost. This
property can be employed for the roughening step in LED manufacture
process, which can significantly enhance light extraction (See,
e.g. "Improved Light Extraction in AlGaInP-Based LEDs Using a
Roughened Window Layer", Ray-Hua Horng, Tzong-Ming Wu, and
Dong-Sing Wuu, Journal of The Electrochemical Society, 155 (10),
(2008) H710-H715 incorporated for all purposes by referenced
herein).
[0041] The conductive Zn(Mg,Cd,Be)O(S,Se) assemblies enlarge the
effective current injection area or light emitting area 310,
enhancing the wall-plug efficiency of the device. This effect can
be seen more explicitly in FIG. 3, where the injected current
pattern is drawn and the light emitting component 300 is detailed.
In FIG. 3, the LED has the first conductive Zn(Mg,Cd,Be)O(S,Se)
assembly 200 attached to the less conductive p-type nitride
semiconductor layer 301, and the second conductive
Zn(Mg,Cd,Be)O(S,Se) assembly 400 replacing the insulative sapphire
substrate 401. The positive electrode 100 and the negative
electrode 500 form Ohmic contacts, respectively, to the first and
the second conductive Zn(Mg,Cd,Be)O(S,Se) assemblies 200 and 400
sandwiching the light emitting component 300. With the conductive
Zn(Mg,Cd,Be)O(S,Se) assemblies, injected current is effectively
spread beyond the electrode (100 and 500) areas. The areas
mentioned here have the same normal as that of the sapphire
substrate surface. Therefore, the effective current injection area
or light emitting area 310 can be approximately equal to the area
of the p-type nitride semiconductor 301 or the area of the active
region 302 where radiative recombination takes place, significantly
larger than that as shown in FIG. 2. Accordingly, the area for
light extraction can be enhanced approximately equal to the area of
the p-type nitride semiconductor 301. As a result, the wall plug in
efficiency is greatly improved.
[0042] The said first conductive Zn(Mg,Cd,Be)O(S,Se) assembly or
the second conductive Zn(Mg,Cd,Be)O(S,Se) assembly can contain
several conductive Zn(Mg,Cd,Be)O(S,Se) layers or bulks of various
shapes, or can only be one conductive Zn(Mg,Cd,Be)O(S,Se) layer.
Each said Zn(Mg,Cd,Be)O(S,Se) layer or bulk may have any of Zn, Mg,
Cd, Be, S, and Se composition the same or different from others.
The said conductive layers or bulks are typically n-type, but could
be p-type. The two electrodes 100 and 500 are preferably metal
alloys composed of Ti, Au, or TiAu alloy. They can also be other
metals or alloys including Al, TiAl, Ni, NiAl, NiAu, Cr, CrAu, and
the like that can form ohmic contact to the
Zn(Mg,Cd,Be)O(S,Se).
[0043] The light emitting component 300 is a combination of
epitaxial semiconductors and is preferably grown by MOCVD or MBE.
It is preferably composed of, in successive layers, an n-type
nitride semiconductor 303, an active region 302 made from nitrides
and containing a single quantum well or multiple quantum wells, and
a p-type nitride semiconductor 301. Here the said nitrides are
group III nitride semiconductors satisfying the formula
Al.sub.xGa.sub.yIn.sub.1-x-yN, inclusive of x=0, y=0, and x=y=0. As
known to some other electronic structures, a quantum well is a well
of potentials which localizes both electrons and holes.
Recombination of electrons and holes in the well(s) results in
light emission. The well(s) is formed by thin layers of nitride
semiconductors satisfying the formula
Al.sub.xGa.sub.yIn.sub.1-x-yN, inclusive of x=0, y=0, and x=y=0. By
adjusting the well width and the compositions, namely x and y of
the said formula Al.sub.xGa.sub.yIn.sub.1-x-yN, inclusive of x=0,
y=0, and x=y=0, the light emitted from the active region can be
ultraviolet, violet, blue, green, yellow, red, and infrared.
Generally, the said light emitting component 300 can comprise of
other layers or configurations for improved quantum efficiency,
which may contain quantum dots as the active media. In addition,
the light emitting component 300 has polarity because it contains a
p-n junction. A positive side and a negative side are thus defined
for the light emitting component 300 with the positive side
referred to the p side and the negative side referred to the n side
of the p-n junction, respectively, as shown in FIG. 1.
[0044] A sacrificial substrate is employed for the growth of the
light emitting component 300. This sacrificial substrate should be
removed after the first conductive Zn(Mg,Cd,Be)O(S,Se) assembly is
formed on the light emitting component 300. The preferable
sacrificial substrate is sapphire or silicon, but in various
embodiments could be any from a group including but not limited to
SiC, Ge, Zn(Mg,Cd,Be)O(S,Se), LiAlO.sub.2, MgAl.sub.2O.sub.4,
ScAlMgO.sub.4, Al.sub.1-x-yIn.sub.xGa.sub.yN (where x=0.about.1,
y=0.about.1), InP, GaAs, quartz, and glass.
[0045] Prior to the growth of the light emitting component 300, a
thin buffer layer is preferably deposited on the said sacrificial
substrate. It can be formed by MOCVD, MBE, VPE, thermal
evaporation, e-beam evaporation, PLD, or sputter. Other deposition
methods may also be used. Although the said thin buffer layer is
primarily to improve the crystallinity of the light emitting
component 300 grown thereon, it may also act as an etch stop for
etch removal of the said sacrificial substrate. The material of the
buffer layer can comprise one of any of nitride semiconductors
satisfying the formula Al.sub.xGa.sub.yIn.sub.1-x-yN, inclusive of
x=0, y=0, and x=y=0, silicon nitride, silicon oxide, silicon
carbide, zirconium nitride, zirconium oxide, zirconium carbide, and
others. As the thin buffer layer may be electrically highly
resistive and adversely affect LED performance, it needs to be
removed to expose the n-type nitride semiconductor 303 that is
electrically conductive. The methods to remove the thin buffer
layer generally include dry and wet etching.
[0046] The first and second conductive Zn(Mg,Cd,Be)O(S,Se)
assemblies 200 and 400 are preferably intentionally doped for
conduction improvement but could comprised of undoped
Zn(Mg,Cd,Be)O(S,Se) since most unintentionally doped
Zn(Mg,Cd,Be)O(S,Se) films and bulks are of n-type and conductive.
The doping sources for conductive Zn(Mg,Cd)O(S,Se) are preferably
Ga compounds, Al compounds, or elemental Ga and Al metals and their
alloys. Other effective doping sources for conductive
Zn(Mg,Cd,Be)O(S,Se) include but are not limited to the compounds of
In, B, Tl, Zn, Cu, Ag, Au, C, Si, Ge, N, P, As, Sb, Pb, F, Cl, Br,
and I, or their elemental forms. Although for most cases, the
doping is done with one doping source, it could be done with two
sources or more. The first conductive Zn(Mg,Cd,Be)O(S,Se) assembly
200 preferably comprises one highly conductive Zn(Mg,Cd,Be)O(S,Se)
layer that attaches onto the positive side of the nitride light
emitting component 300 grown on a sacrificial substrate using
MOCVD.
[0047] Furthermore, at least a layer or a portion of the said
Zn(Mg,Cd,Be)O(S,Se) assemblies 200 and 400 may be doped with
phosphors, forming a compact LED with color conversion and blending
function. The Zn(Mg,Cd,Be)O(S,Se) hosted phosphors therein absorb
the light emitted from the nitride active region 302 and re-emit
light with characteristic wavelengths or colors of their own, which
are different from the color of the original light emitted from the
nitride active region 302. As a result, the output light of the LED
has a color after blending the phosphor-reemitted light and the
original light from the nitride active region 302. One particular
application is white light generation. White light can be
generated, for example, by blending light from a blue LED and
phosphors excited by the blue LED for green and red emission, or by
blending lights from a blue LED and phosphors excited by the blue
LED for yellow emission. Ce.sup.3+ and Eu.sup.2+ could be phosphor
sources for the green and red emissions, respectively. (See,
"Ce.sup.3+/Eu.sup.2+ codoped with Ba.sub.2ZnS.sub.3: A blue
radiation-converting phosphor for white light-emitting diodes",
Woan-Jen Yang and Teng-Ming Chen, Appl. Phys. Lett. 90, (2007)
171908, incorporated by reference herein). Zn, Tb, Cu, and other
transition metals or rare earth ions of various types can also be
effective phosphor sources. Using the Zn(Mg,Cd,Be)O(S,Se)-hosted
phosphors, the color of the output light of the LED can generally
be white, infrared, red, green, yellow, blue, violet, and
ultraviolet portions of the electromagnetic spectrum, depending on
the characteristic wavelengths of the specific phosphors doped, the
absorption effect of the phosphors, and the color and the
brightness of the original light from the said nitride active
region 302.
[0048] Moreover, a roughening process can be applied on the
surfaces or at the interfaces of the vertical LED structure to
improve the LED brightness. Schematically shown in FIG. 4a, total
internal reflection occurs when a ray R1 striking a flat interface
with the angle of incidence .theta. less than the critical angle
.theta.c determined by the refractive indexes of the two media 410
and 420 that form the interface. The light outcoupling efficiency
from a GaN flat surface to air is estimated to be only .about.3%
for a nitride LED because of the total internal reflection (Ref.
"Integrated ZnO nanotips on GaN light emitting diodes for enhanced
emission efficiency", J. Zhong, H. Chen, G. Saraf, and Y. Lu, Appl.
Phys. Lett. 90, (2007) 203515, incorporated herein by reference).
However, light extraction can be significantly enhanced if a
roughened surface or interface is employed. In this case, the
incident angle could locally become more than the critical angle
.theta.c at the incident point, as shown by FIG. 4b. In some
embodiments, a roughening process may or may not be employed at the
interface between the first conductive Zn(Mg,Cd,Be)O(S,Se) assembly
200 and the light emitting component 300. If necessary, the
roughening at the interface can be realized by controlling the
growth conditions such as growth temperature, growth pressure, and
flows of the carrier gas and precursors. Other roughening methods,
such as wet chemical etch or dry etch, can also be used. In
addition, in various embodiments the roughening process can not
only be applied to the interface between the first conductive
Zn(Mg,Cd,Be)O(S,Se) assembly 200 and the light emitting component
300, but also any other surfaces or interfaces of the vertical LED
structure to improve the LED brightness, as long as optical
refractive indexes of the two materials on the two sides of the
surface or the interface is significantly different.
[0049] In other aspects of this invention, the first electrode 100
and the second electrode 500 can be made with various areas and
shapes, depending on specific embodiments of the present invention.
In general, if the majority of the light is extracted from the
upper side via the top surface of the first conductive
Zn(Mg,Cd,Be)O(S,Se) assembly 200, the area of the first electrode
100 connecting to the first conductive Zn(Mg,Cd,Be)O(S,Se) assembly
200 is preferably less than 20% of the total top surface area of
the first conductive Zn(Mg,Cd,Be)O(S,Se) assembly. The second
electrode 500 preferably covers the whole bottom surface of the
second conductive Zn(Mg,Cd,Be)O(S,Se) assembly 400. The second
electrode 500 can act as a reflection mirror such that incident
light can be reflected back towards the surface designed to
efficiently extract the light. The total thickness of the second
electrode 500 should be more than 10 nm and typically less than 500
nm. However, it could be of several hundreds of microns. In this
case the second electrode 500 is also used as a heat sink for heat
dissipation. Vice versa, if the majority of the light is extracted
from the bottom side via the bottom surface of the second
conductive Zn(Mg,Cd,Be)O(S,Se) assembly 400, the area of the second
electrode 500 is preferably less than 20% of the total bottom
surface area of the second conductive Zn(Mg,Cd,Be)O(S,Se) assembly
400. The first electrode 100 preferably covers the whole top
surface of the first conductive Zn(Mg,Cd,Be)O(S,Se) assembly 200.
The first electrode 100 can act as the reflection mirror such that
incident light can be reflected back towards the surface designed
to efficiently extract the light. The total thickness of the second
electrode 100 should be more than 10 nm but typically less than 500
nm. However, the second electrode 100 could have a thickness in the
range of several hundreds of microns or more so that it can also be
used as a heat sink.
[0050] The vertically structured LED and formation methods
according to the present invention are further explained in the
following embodiments, but these are not to be construed to limit
the scope thereof.
[0051] FIG. 5 is a flow chart showing an embodiment of a process
for forming a vertically structured LED integrated with two
conductive Zn(Mg,Cd,Be)O(S,Se) assemblies in accordance with
aspects of the invention. Schematic LED structures based on the
method described in FIG. 5 are shown in FIG. 6a and FIG. 6b with
FIG. 6a for a bottom emission style and FIG. 6b for a top emission
style, respectively.
[0052] Refer to FIG. 5, the light emitting component 300 includes,
but is not limited to an n-type nitride semiconductor 303, an
active region 302 made from nitrides and containing a single
quantum well or multiple quantum wells that are doped or undoped,
and a p-type nitride semiconductor 301. As described from block 501
to block 505, a thin buffer layer 304 and these nitride
semiconductors (303, 302, and 301) of the light emitting component
300 were subsequently grown on a sacrificial substrate using a
preferable growth method, MOCVD. Other growth methods such as HVPE
or MBE may also be used. Here the said nitride is any group III
nitride compound semiconductor satisfying the formula
Al.sub.xGa.sub.yIn.sub.1-x-yN, inclusive of x=0, y=0, and x=y=0.
The preferable sacrificial substrate is sapphire or silicon, but
could be else. Since the thin buffer layer 304 is primarily used
for improving the crystallinity of the nitrides grown thereon and
may also be used as an etch stop for the sacrificial substrate
removal, selection of the buffer layer material relies on
considerations for both. If the substrate material is sapphire,
then the thin buffer layer 304 is preferably GaN, while if the
substrate material is silicon, then the thin buffer layer 304 can
be a combination of thinner AlN and thinner SiN.sub.X layers (See
e.g., "High-performance III-nitride blue LEDs grown and fabricated
on patterned Si substrates", B. Zhang, H. Liang, Y. Wang, Z. Feng,
K. W. Ng, and K. M. Lau, Journal of Crystal Growth 298, (2007)
725-730, incorporated herein by reference.). Additionally, the said
light emitting component 300 may include an n.sup.+ nitride layer
grown on the said p-type nitride semiconductor 301. The top layer
(with exposed surface) of the light emitting component 300 can be
flat or roughened.
[0053] In somewhat more detail, in block 502 a thin buffer layer is
deposited on a sapphire substrate or a silicon substrate. In block
503 an n-type nitride semiconductor is deposited on the buffer
layer. In block 504 a nitride active region including one or more
quantum wells is formed on the n-type nitride semiconductor. In
block 505 a p-type nitride semiconductor is formed on the nitride
active region.
[0054] In block 506, the first conductive Zn(Mg,Cd,Be)O(S,Se)
assembly 200 is formed on the light emitting component 300 with a
flat surface or a roughened surface. This is realized by depositing
a highly conductive Zn(Mg,Cd,Be)O(S,Se) film on the light emitting
component 300, followed by wafer-bonding a conductive
Zn(Mg,Cd,Be)O(S,Se) bulk substrate onto the said highly conductive
Zn(Mg,Cd,Be)O(S,Se) film. The said highly conductive
Zn(Mg,Cd,Be)O(S,Se) film is preferably Ga-doped or Al-doped and
grown by MOCVD, but could be grown by other methods such as MBE,
sputtering, PLD, evaporation, CVD, or the like. The conductive
Zn(Mg,Cd,Be)O(S,Se) substrate is about 150 .mu.m thick with a
portion doped with phosphors. Other thickness of the said
conductive Zn(Mg,Cd,Be)O(S,Se) substrate is also possible. In this
embodiment, the first conductive Zn(Mg,Cd,Be)O(S,Se) assembly is
composed of the highly conductive Zn(Mg,Cd,Be)O(S,Se) film and the
conductive Zn(Mg,Cd,Be)O(S,Se) bulk substrate.
[0055] The wafer-bonding is a technique to firmly join two separate
substances together Each of the two substances preferably has at
least one flat surface that could be used as the bonding interface.
In the present invention, the two separate substances are either
Zn(Mg,Cd,Be)O(S,Se) or nitride semiconductor. In this wafer bonding
process, the said two substances are pressed into contact at room
temperature first with an apparatus, such as a vise, a weight, or
the like, called initial bonding. Then they are heated up to the
bonding temperature preferably of 800.degree. C. where atomic bonds
can be formed at the interface between the two substances. The time
duration at the said bonding temperature is 15 minutes, but could
be longer or shorter. Other bonding temperatures above 300.degree.
C. may also be used. This thermal process is preferably done in a
vacuum apparatus, however it may also be done in an environment
comprising, for example, N.sub.2O, SO.sub.2, H.sub.2S, H.sub.2Se,
NH.sub.3, H.sub.2, oxygen, ozone, water vapor, hydrogen peroxide
vapor, N.sub.2, He, Ne, or Ar. Additionally, an additional layer
201 may be used to improve the bonding interface. This additional
layer 201 can be a thin layer of metal such as Al, Ga, and In or a
metal alloy, preferably with a thickness less than 100 nm. It can
also be a transparent conductive film, such as NiO or ITO. After
the wafer-bonding process, the additional layer 201 may disappear
because the elements in the additional layer 201 could diffuse into
or react with the two substances, namely Zn(Mg,Cd,Be)O(S,Se) or
nitride, during the thermal process. This additional layer 201
should not significantly impede light transmission after the
bonding process.
[0056] After the first conductive Zn(Mg,Cd,Be)O(S,Se) assembly 200
is formed on the light emitting component 300, the sacrificial
substrate and the thin buffer layer are then removed in block 507.
If the material of the sacrificial substrate is sapphire, then the
sacrificial substrate and the thin buffer layer are preferably
removed using a technique called laser lift-off (LLO). In some
embodiments, a pulsed laser is employed for the LLO process with
the wavelength of the dominant emission tuned to 266 nm. The
exposed backside of the sapphire substrate 401 is polished so that
scattering of the laser beam for the LLO is minimized. Then, the
polished sapphire surface is exposed to the 266 nm laser beam with
the beam diameter expanded. This laser beam penetrates the sapphire
401 and strikes the interface between the thin buffer layer 304 and
the sapphire substrate 401. The thin buffer layer 304 preferably
made from GaN usually decomposes after absorption of the laser
beam, yielding mainly metal Ga droplets and nitrogen gas domains at
the interface. After this, the sapphire substrate 401 is lifted off
or removed on a hotplate with a temperature above the melting point
of Ga, 29.78.degree. C. The wavelength of the laser beam for the
LLO process can be varied, as long as it can penetrate the sapphire
substrate 401 without significant absorption, but should be shorter
than the intrinsic absorption wavelength (365.9 nm at room
temperature for GaN) of the buffer material such that the beam can
be absorbed by the buffer material at the interface between the
thin buffer layer 304 and the sapphire substrate 401. A similar LLO
processing has been reported by Chu et al. (Ref. "Study of GaN
Light-Emitting Diodes Fabricated by Laser Lift-off Technique",
Chen-Fu Chu, Fang-I Lai, Jung-Tong Chu, Chang-Chin Yu, Chia-Feng
Lin, Hao-Chung Kuo, and S. C. Wang, Journal of Applied Physics 95,
(2004) 3916-3922, incorporated herein by reference). After the LLO
process, the n-type nitride semiconductor 303 is exposed because
the thin nitride buffer layer 304 has decomposed. In another
aspect, if silicon is used as the sacrificial substrate, LLO can
not be used for the substrate removal because silicon is opaque to
the UV laser beam. However, the silicon substrate and the thin
buffer layer can be removed using, for example, an lapping and
etching combined (LEC) process as follows: 1) Use a mechanical
lapping method to thin the silicon wafer down to less than 50
microns with the first Zn(Mg,Cd,Be)O(S,Se) assembly protected, for
example, by wax; 2) Remove the rest silicon by the well known HNA
isotropic, wet etching method using the buffer layer as the etch
stop (See e.g. "Fabrication of suspended GaN microstructures using
GaN-on-patterned-silicon (GPS) technique", Z. Yang, R. N. Wang, S.
Jia, D. Wang, B. S. Zhang, K. M. Lau, and K. J. Chen, Physica
Status Solidi (a) 203, (2006) 1712-1715, incorporated herein by
reference); 3) Remove the protection wax and use acetone and other
solvents to clean the wax residue; 4) Remove the thin buffer layer
by dry etching with a low etching rate to expose the n-type nitride
semiconductor 303. (See e.g. "Hig rate etching of MN using
BCl.sub.3/Cl.sub.2/Ar inductively coupled plasma", F. A. Khan, L.
Zhou, V. Kumar, I. Adesida, and R. Okojie, Materials Science and
Engineering B95, (2002) 51-54, incorporated herein by
reference).
[0057] In block 508, the aforementioned wafer bonding process is
employed again to wafer-bond the second conductive
Zn(Mg,Cd,Be)O(S,Se) assembly 400 to the exposed surface of the
n-type nitride semiconductor 303. The second conductive
Zn(Mg,Cd,Be)O(S,Se) assembly 400 is preferably a 150 .mu.m thick,
conductive Zn(Mg,Cd,Be)O(S,Se) substrate with a portion doped by
phosphors. The conductive Zn(Mg,Cd,Be)O(S,Se) assembly 400 can also
be a Zn(Mg,Cd,Be)O(S,Se) bulk or bulks with shapes of various
types, a layer or several layers of Zn(Mg,Cd,Be)O(S,Se), or their
combinations.
[0058] In block 509, the positive and negative electrodes 100 and
500 are formed and connected to the first and the second conductive
Zn(Mg,Cd,Be)O(S,Se) assemblies 200 and 400, respectively, as shown
by FIG. 6a and FIG. 6b using conventional semiconductor device
fabrication processes. Herein, the conventional semiconductor
device processing generally includes, but is not limited to,
lithography, evaporation, etching, CVD, and thermal annealing. FIG.
6a schematically shows an LED of this embodiment, which emits light
downwards. The positive electrode 100 is used not only as an
electrode but also a light reflector. For this LED, the majority of
the emitted light is extracted from the second conductive
Zn(Mg,Cd,Be)O(S,Se) assembly 400. In contrast, FIG. 6b
schematically shows another LED of this embodiment with light
emitting upwards. Therein the negative electrode 500 is used not
only as an electrode but also a light reflector. Most light of the
LED is extracted from the first conductive Zn(Mg,Cd,Be)O(S,Se)
assembly 100.
[0059] FIG. 7 is a flow chart showing an embodiment of a process of
forming a vertically structured LED integrated with one conductive
Zn(Mg,Cd,Be)O(S,Se) assembly in accordance with aspects of the
invention. Schematic LED structures based on the method described
in FIG. 7 are shown in FIG. 8a and FIG. 8b with FIG. 8a for a
bottom emission style and FIG. 8b for a top emission style,
respectively.
[0060] Refer to FIG. 7, the light emitting component 300 includes,
but is not limited to an n-type nitride semiconductor 303, an
active region 302 made from nitrides and containing a single
quantum well or multiple quantum wells that are doped or undoped,
and a p-type nitride semiconductor 301. As described from block 701
to block 705, a thin buffer layer 304 and these nitride
semiconductors (303, 302, and 301) of the light emitting component
300 were subsequently grown on a sacrificial substrate using a
preferable growth method, MOCVD. Other growth methods such as HVPE
or MBE may also be used for the growth. Herein the said nitrides
are any group III nitride compound semiconductors satisfying the
formula Al.sub.xGa.sub.yIn.sub.1-x-yN, inclusive of x=0, y=0, and
x=y=0. The said sacrificial substrate is preferably a sapphire
substrate or a silicon substrate, but could be else. And the
material of the thin buffer layer 304 generally depends on the
substrate type. If the substrate material is sapphire, then the
thin buffer layer 304 is preferably GaN, while if the substrate
material is silicon, then the thin buffer layer 304 can be a
combination of thinner AlN and thinner SiN.sub.X layers.
Additionally, the said light emitting component 300 may include an
n.sup.+ nitride layer grown on the said p-type nitride
semiconductor 301. The top layer (with exposed surface) of the
light emitting component 300 can be flat or roughened.
[0061] In block 706, the first conductive Zn(Mg,Cd,Be)O(S,Se)
assembly 200 is formed on the surface of the said light emitting
component 300. This is realized by depositing a highly conductive
Zn(Mg,Cd,Be)O(S,Se) film on the light emitting component 300,
followed by wafer-bonding a conductive Zn(Mg,Cd,Be)O(S,Se) bulk
substrate onto the said highly conductive Zn(Mg,Cd,Be)O(S,Se) film.
The surface of the said light emitting component 300 can be flat or
roughened. The said highly conductive Zn(Mg,Cd,Be)O(S,Se) film is
preferably Ga-doped or Al-doped and grown by MOCVD, but could be
grown by other methods such as MBE, sputtering, PLD, or the like.
The said conductive Zn(Mg,Cd,Be)O(S,Se) substrate is about 150
.mu.m thick with a portion doped with phosphors. Other thickness of
the said conductive Zn(Mg,Cd,Be)O(S,Se) substrate is also possible.
The first conductive Zn(Mg,Cd,Be)O(S,Se) assembly herein is
composed of the said highly conductive Zn(Mg,Cd, Be)O(S,Se) film
and the said conductive Zn(Mg,Cd,Be)O(S,Se) bulk substrate.
[0062] In block 707, the said sacrificial substrate and the thin
buffer layer thereon are then removed. Sapphire and silicon are the
preferable substrates. If sapphire is used, then it can be removed
preferably using the said laser lift-off (LLO) technique. The
n-type nitride semiconductor 303 is exposed after the LLO process
because the thin nitride (GaN) buffer layer 304 has decomposed
during the LLO process. In another aspect, if silicon is used, the
substrate and the thin buffer layer can be removed using the said
LEC process.
[0063] Then in block 708, the positive and negative electrodes 100
and 500 are formed connecting to the first conductive
Zn(Mg,Cd,Be)O(S,Se) assembly and the exposed n-type nitride 303,
respectively, as shown by FIG. 8a and FIG. 8b using conventional
semiconductor device fabrication process. Herein, the said
conventional semiconductor device processing includes, but is not
limited to, lithography, evaporation, etching, CVD, and thermal
annealing. FIG. 8a schematically shows an LED of this embodiment,
which emits light downwards. In this configuration, the positive
electrode 100 is used not only as an electrode but also a light
reflector. The majority of light is extracted from the n-type
nitride semiconductor 303. In contrast, FIG. 8b schematically shows
another LED of this embodiment with light emitting upwards. Therein
the negative electrode 500 is used not only as an electrode but
also a light reflector. Most light of the LED is extracted from the
first conductive Zn(Mg,Cd,Be)O(S,Se) assembly 100.
[0064] FIG. 9 and FIG. 10 illustrate some of the advantages of the
LEDs designed and manufactured according to the present invention.
These two figures illustrate data measured from the said LEDs of
the present invention and the reference LEDs, respectively. The
reference LEDs were manufactured based on the conventional LED
structure as shown in FIG. 3. For comparison, the said LEDs of the
present invention and the said reference LEDs employed the same
light emission component 300, grown in the same MOCVD growth run.
FIG. 9 shows the said LEDs of the present invention are brighter
and more efficient than the said reference LEDs, as shown by higher
light output power at a given input electrical power. FIG. 10 shows
the said LEDs of the present invention are more color stable. Given
a specified emission wavelength tolerance of .+-.3 nm, the said
LEDs of the present invention have a larger operational light
output power range from 0 to 23 mW, while the said reference LEDs
have a lower operational light output power range from 0 to 15
mW.
[0065] Although the present invention has been described in
considerable detail with reference to certain preferred embodiments
thereof, other versions are possible. Other LED structures
integrating nitride semiconductor lighting component with
conductive Zn(Mg,Cd,Be)O(S,Se) can also be envisioned by one
skilled in the art. The new LED can have different arrangements of
Zn(Mg,Cd,Be)O(S,Se) layers or assemblies, different methods of
integrating Zn(Mg,Cd,Be)O(S,Se) and nitride semiconductor,
different growth methods of Zn(Mg,Cd,Be)O(S,Se) and nitride
semiconductor layers, different doping methods, different
roughening features, and different locations of the roughened
surfaces. Therefore, the spirit and scope of the appended claims
should not be limited to the preferred embodiments described
herein.
* * * * *