U.S. patent application number 11/762985 was filed with the patent office on 2007-12-27 for gallium nitride material devices and methods of forming the same.
This patent application is currently assigned to Nitronex Corporation. Invention is credited to Kevin J. Linthicum, T. Warren JR. Weeks.
Application Number | 20070295985 11/762985 |
Document ID | / |
Family ID | 34273355 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070295985 |
Kind Code |
A1 |
Weeks; T. Warren JR. ; et
al. |
December 27, 2007 |
GALLIUM NITRIDE MATERIAL DEVICES AND METHODS OF FORMING THE
SAME
Abstract
The invention provides gallium nitride material devices,
structures and methods of forming the same. The devices include a
gallium nitride material formed over a substrate, such as silicon.
Exemplary devices include light emitting devices (e.g., LED's,
lasers), light detecting devices (such as detectors and sensors),
power rectifier diodes and FETs (e.g., HFETs), amongst others.
Inventors: |
Weeks; T. Warren JR.;
(Raleigh, NC) ; Linthicum; Kevin J.; (Cary,
NC) |
Correspondence
Address: |
WOLF GREENFIELD & SACKS, P.C.
600 ATLANTIC AVENUE
BOSTON
MA
02210-2206
US
|
Assignee: |
Nitronex Corporation
Durham
NC
|
Family ID: |
34273355 |
Appl. No.: |
11/762985 |
Filed: |
June 14, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10650122 |
Aug 25, 2003 |
7233028 |
|
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11762985 |
Jun 14, 2007 |
|
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09792414 |
Feb 23, 2001 |
6611002 |
|
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10650122 |
Aug 25, 2003 |
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Current U.S.
Class: |
257/183 ;
257/103; 257/E21.366; 257/E21.407; 257/E29.022; 257/E33.025;
257/E33.07 |
Current CPC
Class: |
H01L 29/0657 20130101;
H01L 2924/10155 20130101; H01S 5/32341 20130101; H01L 29/66204
20130101; H01L 29/417 20130101; H01L 31/03044 20130101; H01L
31/1856 20130101; H01L 33/0093 20200501; Y02E 10/544 20130101; H01L
33/007 20130101; H01L 47/026 20130101; H01L 29/2003 20130101; H01L
33/20 20130101; H01S 5/04254 20190801; H01L 33/32 20130101; H01L
29/861 20130101; H01L 29/66462 20130101; H01L 31/03048 20130101;
H01L 33/382 20130101; H01L 29/802 20130101; H01L 29/7786 20130101;
H01L 33/38 20130101; H01L 31/1848 20130101; H01S 5/0207
20130101 |
Class at
Publication: |
257/103 ;
257/E33.025; 257/E33.07 |
International
Class: |
H01L 33/00 20060101
H01L033/00 |
Claims
1. A semiconductor device comprising: a substrate; and a gallium
nitride material region formed over the substrate, wherein the
semiconductor device has at least one via extending from a first
side of the semiconductor device, wherein the via is free of an
electrical contact formed therein.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/650,122, filed Aug. 25, 2003, and entitled
"Gallium Nitride Material Devices and Methods of Forming the Same",
which is a continuation-in-part of U.S. patent application Ser. No.
09/792,414 (now U.S. Pat. No. 6,611,002), filed Feb. 23, 2001, and
entitled "Gallium Nitride Material Devices and Methods Including
Backside Vias". All of the above-mentioned disclosures are
incorporated herein by reference.
FIELD OF INVENTION
[0002] The invention relates generally to semiconductor materials
and, more particularly, to gallium nitride materials and methods of
producing gallium nitride materials.
BACKGROUND OF INVENTION
[0003] Gallium nitride materials include gallium nitride (GaN) and
its alloys such as aluminum gallium nitride (AlGaN), indium gallium
nitride (InGaN), and aluminum indium gallium nitride (AlInGaN).
These materials are semiconductor compounds that have a relatively
wide, direct bandgap which permits highly energetic electronic
transitions to occur. Such electronic transitions can result in
gallium nitride materials having a number of attractive properties
including the ability to efficiently emit visible (e.g., blue,
green) or UV light, the ability to transmit signals at high
frequency, and others. Accordingly, gallium nitride materials are
being widely investigated in many semiconductor device applications
such as transistors, field emitters, and optoelectronic
devices.
[0004] Gallium nitride materials have been formed on a number of
different substrates including silicon carbide (SiC), sapphire, and
silicon. Silicon substrates are readily available and relatively
inexpensive, and silicon processing technology has been well
developed. However, forming gallium nitride materials on silicon
substrates to produce semiconductor devices presents challenges
which arise from differences in the lattice constant, thermal
expansion, and band gap between silicon and gallium nitride.
SUMMARY OF INVENTION
[0005] The invention includes providing gallium nitride material
structures, devices and methods of forming the structures and
devices.
[0006] In one aspect, a semiconductor device is provided. The
device comprises a substrate, and a gallium nitride material region
formed over the substrate. The semiconductor device has at least
one via extending from a first side of the semiconductor device,
wherein the via is free of an electrical contact formed
therein.
[0007] In another aspect, a method of forming a semiconductor
device is provided. The method comprises forming a gallium nitride
material region over a substrate, and forming a via extending from
a first side of the semiconductor device. The via is free of an
electrical contact formed therein.
[0008] In another aspect, a semiconductor device is provided. The
semiconductor device comprises a silicon substrate and a gallium
nitride material region formed over the silicon substrate. The
device further comprises a first electrical contact formed over a
portion of the gallium nitride material region, and a second
electrical contact formed over a portion of the gallium nitride
material region. The semiconductor device has at least one via
extending from a backside of the semiconductor device.
[0009] In another aspect, a method of forming a semiconductor
device is provided. The method comprises forming a gallium nitride
material region over a silicon substrate, forming a first
electrical contact over the gallium nitride material region, and
forming a second electrical contact over the gallium nitride
material region. The method further comprises forming a via
extending from a backside of the semiconductor device.
[0010] In another aspect, an opto-electronic device is provided.
The opto-electronic device comprises a silicon substrate, a
compositionally-graded transition layer formed over the silicon
substrate, and a gallium nitride material region formed over the
compositionally-graded transition layer. The gallium nitride
material region includes an active region.
[0011] In another aspect, a method of forming a opto-electronic
device is provided. The method comprises forming a
compositionally-graded transition layer formed over a silicon
substrate, and forming a gallium nitride material region over the
compositionally-graded transition layer. The gallium nitride
material region includes an active region.
[0012] In another aspect, a method of forming a semiconductor
structure is provided. The method comprises forming a first
transition layer over a silicon substrate, forming a gallium
nitride material region over the first transition layer, and
removing the silicon substrate to expose a backside of the
transition layer.
[0013] In another aspect, an opto-electronic device is provided.
The opto-electronic device comprises a transition layer comprising
a gallium nitride alloy, aluminum nitride, or an aluminum nitride
alloy. The transition layer has an exposed back surface. The device
further comprises a gallium nitride material region formed over a
front surface of the transition layer. The gallium nitride material
region includes an active region.
[0014] In another aspect, an opto-electronic device is provided.
The opto-electronic device comprises a transition layer comprising
a gallium nitride alloy, aluminum nitride, or an aluminum nitride
alloy. The device further comprises an electrical contact formed
directly on a back surface of the transition layer, and a gallium
nitride material region formed over a front surface of the
transition layer. The gallium nitride material region includes an
active region.
[0015] In another aspect, an opto-electronic device is provided.
The opto-electronic device comprises a silicon substrate, a gallium
nitride material region formed over the substrate. The gallium
nitride material region includes an active region, wherein the
active region has a non-rectangular plane-view cross-section.
[0016] In another aspect, an opto-electronic device is provided.
The opto-electronic device comprises a substrate, a gallium nitride
material region formed over the substrate. The gallium nitride
material region includes an active region, wherein the active
region has a non-rectangular plane-view cross-section. A non-active
region of the opto-electronic device has a non-rectangular
plane-view cross-section.
[0017] In another aspect, a method is provided. The method
comprises forming an active region having a non-rectangular
plane-view cross-section. The active region is a portion of a
gallium nitride material region formed on a silicon substrate.
[0018] In another aspect, a method is provided. The method
comprises forming an active region having a non-rectangular
plane-view cross-section. The active region is a portion of a
gallium nitride material region formed on a substrate. The method
further comprises forming a non-active region having a
non-rectangular plane-view cross-section.
[0019] Other aspects, embodiments and features of the invention
will become apparent from the following detailed description of the
invention when considered in conjunction with the accompanying
drawings. The accompanying figures are schematic and are not
intended to be drawn to scale. In the figures, each identical, or
substantially similar component that is illustrated in various
figures is represented by a single numeral or notation. For
purposes of clarity, not every component is labeled in every
figure. Nor is every component of each embodiment of the invention
shown where illustration is not necessary to allow those of
ordinary skill in the art to understand the invention. All patent
applications and patents incorporated herein by reference are
incorporated by reference in their entirety. In case of conflict,
the present specification, including definitions, will control.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 illustrates a semiconductor device including a
backside via according to one embodiment of the present
invention.
[0021] FIG. 2 illustrates a semiconductor device including multiple
backside vias according to another embodiment of the present
invention.
[0022] FIG. 3 illustrates a semiconductor device including multiple
backside vias and no topside vias according to another embodiment
of the present invention.
[0023] FIG. 4 illustrates an LED according to another embodiment of
the present invention.
[0024] FIG. 5 illustrates a laser diode according to another
embodiment of the present invention.
[0025] FIG. 6 illustrates a power rectifier diode according to
another embodiment of the present invention.
[0026] FIG. 7 illustrates a double-gate HFET according to another
embodiment of the present invention.
[0027] FIG. 8 illustrates an LED including multiple backside vias
and no topside vias according to another embodiment of the present
invention.
[0028] FIG. 9 illustrates a semiconductor device including a
backside via free of an electrical contact according to another
embodiment of the present invention.
[0029] FIG. 10 illustrates a semiconductor device including a
backside via having a backside via that is shaped to enhance
internal reflection of light according to another embodiment of the
present invention.
[0030] FIG. 11 illustrates a semiconductor device including a
positive and negative contact formed on a backside of the device
according to another embodiment of the present invention.
[0031] FIG. 12 illustrates a semiconductor device after the
substrate has been removed during processing according to another
embodiment of the present invention.
[0032] FIG. 13 illustrates a light emitting device that includes
two topside contacts according to another embodiment of the present
invention.
[0033] FIG. 14 illustrates a light emitting device including two
topside contacts according to another embodiment of the present
invention.
[0034] FIG. 15 illustrates a light emitting device after the
substrate has been removed during processing according to another
embodiment of the present invention.
[0035] FIG. 16 illustrates a light emitting device including a
reflector region according to another embodiment of the present
invention.
[0036] FIG. 17 illustrates a light emitting device including a
reflector region according to another embodiment of the present
invention.
[0037] FIG. 18 illustrates a light emitting device including a
medium containing phosphor according to another embodiment of the
present invention.
[0038] FIG. 19 illustrates a light emitting device including a
reflector region formed within a via according to another
embodiment of the present invention.
[0039] FIG. 20 illustrates a light emitting device that has been
flipped during use according to another embodiment of the present
invention.
[0040] FIG. 21 illustrates an LED designed to emit UV light
according to another embodiment of the present invention.
[0041] FIG. 22 illustrates a view of a backside the device of FIG.
1.
[0042] FIGS. 23A-23K illustrate a series of plane-view
cross-sections of respective active regions of opto-electronic
devices according to additional embodiments of the invention.
[0043] FIG. 24 illustrates an opto-electronic device including an
active region according to another embodiment of the invention.
[0044] FIG. 25 illustrates a light emitting device that is mounted
to a carrier according to another embodiment of the present
invention.
[0045] FIG. 26 illustrates a semiconductor device according to an
embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0046] The invention provides gallium nitride material structures,
devices and methods of forming the structures and devices.
[0047] Referring to FIG. 1, a semiconductor device 10 according to
one embodiment of the invention is shown. Semiconductor device 10
includes a substrate 12 and a gallium nitride material device
region 14 formed over the substrate. As described further below,
device structures are typically formed, at least in part, within
gallium nitride material region 14. Device 10 further includes a
transition layer 15 formed on substrate 12, for example, to
facilitate the subsequent deposition of gallium nitride material
device region 14. In some cases, the transition layer (or, at least
a portion of the transition layer) may be non-conducting. A topside
electrical contact 16 (on a topside 18 of the device) and a
backside electrical contact 20 (on a backside 22 of the device) are
provided for connection to an external power supply that powers the
device. Backside contact 20 is deposited within a via 24 that
extends from backside 22 of the device. Via 24 extends through
transition layer 15 and into a conducting region (e.g., device
region 14) within device 10. As a result of the deposition of
backside contact 20 within via 24, current can flow between the
backside contact and topside contact 16 through device region 14
without being blocked by transition layer 15, when the transition
layer is non-conducting. Thus, vertical conduction through device
10 between backside contact 20 and topside contact 16 may be
achieved despite the presence of a non-conducting transition layer
15.
[0048] FIG. 22 illustrates a view of backside 22 of device 10.
[0049] As used herein, "non-conducting" refers to a layer that
prevents current flow or limits current flow to negligible amounts
in one or more directions. "Non-conducting" layers, for example,
may be formed of non-conductor materials, or may be formed of
semiconductor materials which have a band sufficiently offset from
the layer adjacent the "non-conducting" layer. A "non-conducting"
layer may be conductive in and of itself, but may still be
non-conducting (e.g., in a vertical direction) as a result of a
band offset or discontinuity with an adjacent layer. As used
herein, "vertical conduction" refers to electrical current flow in
a vertical direction within a device. "Vertical conduction" may be
between backside contact and topside contact or may be between
different layers within the device that are separated
vertically.
[0050] It should be understood that when a layer is referred to as
being "on" or "over" another layer or substrate, it can be directly
on the layer or substrate, or an intervening layer also may be
present. A layer that is "directly on" another layer or substrate
means that no intervening layer is present. It should also be
understood that when a layer is referred to as being "on" or "over"
another layer or substrate, it may cover the entire layer or
substrate, or a portion of the layer or substrate.
[0051] As shown in the figures, the term "topside" refers to the
upper surface of a structure or device and the term "backside"
refers to the bottom surface of a structure or device. It should be
understood that the substrate also has a "topside" and a
"backside." When processing a typical structure, layer(s) are grown
from the topside of the substrate and the resulting upper growth
surface defines the topside of the structure or device. In some
cases, during use, a device may be flipped so that its backside
faces upward and its topside faces downward (e.g., See FIG. 20). In
these "flip chip" embodiments, the topside of the device may be
mounted to another surface (e.g., to provide a source of power to
electrodes on the topside).
[0052] In certain preferred embodiments, substrate 12 is a silicon
substrate. As used herein, silicon substrate 14 refers to any
substrate that includes a silicon layer. Examples of suitable
silicon substrates include substrates that are composed entirely of
silicon (e.g., bulk silicon wafers), silicon-on-insulator (SOI)
substrates, silicon-on-sapphire substrate (SOS), and SIMOX
substrates, amongst others. Suitable silicon substrates also
include substrates that have a silicon wafer bonded to another
material such as diamond, AlN, or other polycrystalline materials.
Silicon substrates having different crystallographic orientations
may be used. In some cases, silicon (111) substrates are preferred.
In other cases, silicon (100) substrates are preferred.
[0053] It should be understood that in other embodiments,
substrates other than silicon substrates may be used such as
sapphire and silicon carbide substrates.
[0054] Substrate 12 may have any suitable dimensions and its
particular dimensions are dictated by the application. Suitable
diameters include, but are not limited to, 2 inches (50 mm), 4
inches (100 mm), 6 inches (150 mm), and 8 inches (200 mm). In some
embodiments, silicon substrate 12 is relatively thick, for example,
greater than 250 microns. Thicker substrates are generally able to
resist bending which can occur, in some cases, in thinner
substrates. In some embodiments, silicon substrate 12 is preferably
thin, for example less than 250 microns, or less than 100 microns,
to facilitate the formation of via 24 therethrough.
[0055] Transition layer 15 may be formed on substrate 12 prior to
the deposition of gallium nitride material device region 14, for
example, to accomplish one or more of the following: reducing crack
formation in gallium nitride material device region 14 by lowering
thermal stresses arising from differences between the thermal
expansion rates of gallium nitride materials and the substrate;
reducing defect formation in gallium nitride material device region
14 by lowering lattice stresses arising from differences between
the lattice constants of gallium nitride materials and the
substrate; and, increasing conduction between substrate 12 and
gallium nitride material device region 14 by reducing differences
between the band gaps of substrate 12 and gallium nitride
materials. The presence of transition layer 15 may be particularly
preferred when utilizing silicon substrates because of the large
differences in thermal expansion rates and lattice constant between
gallium nitride materials and silicon. It should be understood that
transition layer 15 also may be formed between substrate 12 and
gallium nitride material device region for a variety of other
reasons. As noted above, transition layer 15 may be non-conducting,
although, in some cases, transition layer 15 may be conducting.
[0056] The composition of transition layer 15 depends, at least in
part, upon the type of substrate and the composition of gallium
nitride material device region 14. In some embodiments which
utilize a silicon substrate, transition layer 15 may preferably
comprise a compositionally-graded transition layer having a
composition that is varied across at least a portion of the layer.
Suitable compositionally-graded transition layers, for example,
have been described in co-pending, commonly-owned, U.S. patent
application Ser. No. 09/736,972, entitled "Gallium Nitride
Materials and Methods," filed on Dec. 14, 2000, which is
incorporated herein by reference. Compositionally-graded transition
layers are particularly effective in reducing crack formation in
gallium nitride material device region 14 by lowering thermal
stresses that result from differences in thermal expansion rates
between the gallium nitride material and substrate 12 (e.g.,
silicon). In some embodiments, when compositionally-graded,
transition layer 15 is formed of an alloy of gallium nitride such
as Al.sub.xIn.sub.yGa.sub.(1-x-y)N, Al.sub.xGa.sub.(1-x)N, or
In.sub.yGa.sub.(1-y)N. In these embodiments, the concentration of
at least one of the elements (e.g., Ga, Al, In) of the alloy is
typically varied across at least a portion of the cross-sectional
thickness of the layer.
[0057] In other embodiments, transition layer 15 has a constant
(i.e., non-varying) composition across its thickness. Such layers
may be referred to as buffer layers and/or intermediate layers.
Suitable intermediate layers, for example, have been described in
U.S. patent application Ser. No. 09/736,972, referenced above. In
some embodiments, transition layer 15 has a constant composition of
a gallium nitride alloy (such as Al.sub.xIn.sub.yGa.sub.(1-x-y)N,
Al.sub.xGa.sub.(1-x)N, or In.sub.yGa.sub.(1-y)N), aluminum nitride,
or an aluminum nitride alloy.
[0058] In the illustrative embodiment of FIG. 1, a single
transition layer 15 is shown between substrate 12 and gallium
nitride material device region 14. Other embodiments may include
more than one transition layer. For example, as shown in FIG. 2,
device 10a may include a compositionally-graded transition layer
15a formed on (in some cases, directly on) a transition layer 15b
having a constant composition (e.g., an intermediate layer of a
gallium nitride alloy, aluminum nitride, or an aluminum nitride
alloy). It should also be understood that constant composition
transition layer 15b may be formed on (in some cases, directly on)
compositionally-graded transition layer 15a. In some cases, the
device may include two constant composition transition layers--for
example, a first formed on the compositionally-graded transition
layer and a second formed on the substrate under the
compositionally-graded transition layer.
[0059] It also should be understood that in some embodiments, one
or more other types of layers (including conducting layers) may be
present between substrate 12 and gallium nitride material device
region 14 which may accomplish one or more of the above-described
features of the transition layer. In some cases, the transition
layer is the sole layer between the substrate and the gallium
nitride material device region. In embodiments, that include one or
more conducting layer, the structure may not include any
non-conducting layers.
[0060] In the embodiment of FIG. 1, via 24 extends through
transition layer 15 of substrate 12 so that vertical conduction can
occur in device 10 even when the transition layer is
non-conducting. Thus, in these embodiments, at a minimum, via 24
has a length (L) sufficient to create a conducting vertical path
between topside contact 16 and backside contact 20. Via 24, for
example, may extend to a position within gallium nitride material
device region 14 to form such a conducting path. In some cases, it
may be preferable to have via 24 extend to an etch-stop layer
(e.g., See 46, FIG. 5) within gallium nitride material device
region 14, to facilitate processing as described further below. In
certain embodiments, via 24 may extend to a position below gallium
nitride material device layer--for example, within an upper portion
of a doped, conductive transition layer and, thus, a vertical
conducting path is formed. In some cases, via 24 may extend to a
source region or a drain region formed within device 10.
[0061] The exact dimensions and shape of via 24 depend upon the
application. A typical cross-sectional area of via is about 100
microns by about 100 microns at backside 22. The cross-sectional
area of the via may be square (as shown in FIG. 22), circular or
another shape. It may be preferable for via 24 to be tapered
inward, as shown, thus giving the via a cone shape (i.e., a
truncated pyramid shape). The inward taper (i.e., a cross-sectional
area that decreases in a direction away from the backside) can
facilitate deposition of backside contact 20 on side walls 28 of
via 24 and may also, in some cases, be beneficial for enhancing
light extraction. In other cases, as described further below and
shown in FIG. 10, it may be preferable for the via to be tapered
outward (i.e., a cross-sectional area that increases in a direction
away from the backside). An outwardly tapered via may enhance
internal light reflection which can improve light extraction in
certain embodiments. In some cases, it may be preferable to have
via 24 positioned away from sides 29 of the device. That is, the
via does not intersect with a side of the device.
[0062] In FIG. 1, device 10 includes a single via 24. Other
embodiments, however, as described further below and shown in FIGS.
2-3, may include more than one via.
[0063] As used herein, the phrase "electrical contact" or "contact"
refers to any conducting structure on a semiconductor device that
is designed to be contacted by a power source. "Contacts" may also
be referred to as electrodes, terminals, contact pads, contact
areas, contact regions and the like. It should be understood that
certain types of conducting structures that are on, or part of, a
semiconductor device are not electrical contacts, as used herein.
For example, conducting regions or layers (e.g., reflector layer
120 in some cases) that are not contacted by a power source during
use are not electrical contacts as defined herein.
[0064] Backside contact 20 and topside contact 16 are formed of
conducting materials including certain metals. Any suitable
conducting material known in the art may be used. The composition
of contacts 16, 20 may depend upon the type of contact. For
example, contacts 16, 20 may contact n-type material or p-type
material. Suitable metals for n-type contacts include titanium,
nickel, aluminum, gold, copper, and alloys thereof. Suitable metals
for p-type contacts include nickel, gold, and titanium, and alloys
thereof.
[0065] Contacts 16, 20 have a thickness sufficient to ensure that
the contact is electrically conductive across its entire physical
area. Suitable thicknesses for contacts 16, 20, for example, are
between about 0.05 microns and about 10 microns. In some cases, the
thickness of backside contact 20 may vary over its area because of
uneven deposition on side walls 28 of via 24. The surface areas of
backside contact 20 and topside contact 16 are generally sufficient
so that the contacts can be contacted by terminals of an
appropriate power source through wire bonding, air bridging and the
like. In certain preferred embodiments, backside contact 20
substantially extends only over backside and does not, for example,
extend over sides 30 of device 10. Thus, in these preferred
embodiments, sides 30 are substantially free of backside contact
20.
[0066] In some embodiments, as described further below,
semiconductor structure may include one or more backside contact
and no topside contact (e.g., FIG. 3), or one or more topside
contact (e.g., two for light emitting devices or three for FETs)
and no backside contact (e.g., FIGS. 13-16).
[0067] In some embodiments, contacts 16, 20 also may function as an
effective heat sink. In these embodiments, contacts 16, 20 remove
thermal energy generated during the operation of the device. This
may enable device 10 to operate under conditions which generate
amounts of heat that would otherwise damage the device. In
particular, laser diodes that operate at high current densities may
utilize contacts 16, 20 as a heat sink. Contacts 16, 20 may be
specifically designed to enhance thermal energy removal. For
example, contacts 16, 20 may be composed of materials such as
copper and gold, which are particularly effective at removing heat.
Also, contacts 16, 20 may be designed so that a large surface area
is in contact with device region 14 for example, by including
multiple vias and/or vias that extend significantly into device
region 14.
[0068] In some embodiments, such as when device 10 is an
opto-electronic device, contacts 16, 20 can function as a reflector
region (e.g., 120a, FIG. 19), as described further below. By
reflecting light generated by the device, contacts 16, 20 can
direct the light in a desired direction, for example, out of
topside 18, backside 22, and/or sides 30 of device 10 depending on
the design of the device. Thus, the output efficiency of the device
may be enhanced. In particular, laser diodes and light emitting
diodes can benefit from utilizing the reflective properties of
contacts 16, 20. To enhance the ability of backside contact 20 to
reflect light, for example, via 24 is formed such that the backside
contact extends proximate an active region (e.g., 38, FIG. 4; 50,
FIG. 5).
[0069] As used herein, the term "active region," when used in
connection with a light emitting device, refers to a light
generating region, and when used in connection with a light
detecting device refers to a light collecting region.
[0070] In certain embodiments, and as described further below in
connection with FIGS. 9-11, 13-14, and 16-18, it may be preferable
for via 24 to be free of a contact. That is, a contact is not
formed within the via. In some cases, the via may be free of a
contact but may have one or more other region(s) or layer(s) formed
therein (e.g., a reflective layer), as described further below. In
some cases, the via may be free of any material formed therein.
When free of material, the via may function as a window that
exposes internal layers of the device (e.g., transition layer 15 or
gallium nitride material device region 14) to the outside. This
exposure may enhance the extraction of light from the device which
can be particularly useful in light-emitting devices such as LEDs
or lasers. In embodiments in which via 24 is free of an electrical
contact, it should be understood that contacts are formed on other
parts of the device including other (non-via) areas of backside 22
or areas of topside 18.
[0071] In some cases, to maximize exposure of the internal device
layers, substrate 12 may be entirely removed, for example, by
etching (wet or dry) or grinding. Such a device is shown in FIGS.
12, 15 and 25, and described further below. When the substrate is
entirely removed, it may be desirable to mount, or bond, the
structure to a carrier which may be a wafer (e.g., silicon or GaAs)
that provides rigidity and/or support during further processing,
handling, or use. The rigidity and/or support provided by the
carrier result from its relatively large thickness compared to the
thickness of the remaining structure. In some cases, carriers may
also function as a reflector region.
[0072] Gallium nitride material device region 14 comprises at least
one gallium nitride material layer. In some cases, gallium nitride
material device region 14 includes only one gallium nitride
material layer. In other cases, as described further below and
shown in FIGS. 4-8, gallium nitride material device region 14
includes more than one gallium nitride material layer. The
different layers can form different regions of the semiconductor
structure. Gallium nitride material region 14 also may include one
or more layers that do not have a gallium nitride material
composition such as other III-V compounds or alloys, oxide layers,
and metallic layers.
[0073] As used herein, the phrase "gallium nitride material" refers
to gallium nitride (GaN) and any of its alloys, such as aluminum
gallium nitride (Al.sub.xGa.sub.(1-x)N), indium gallium nitride
(In.sub.yGa.sub.(1-y)N), aluminum indium gallium nitride
(Al.sub.xIn.sub.yGa.sub.(1-x-y)N), gallium arsenide phosphoride
nitride (GaAs.sub.aP.sub.b N.sub.(1-a-b)), aluminum indium gallium
arsenide phosphoride nitride
(Al.sub.xIn.sub.yGa.sub.(1-x-y)As.sub.aP.sub.bN.sub.(1-a-b)),
amongst others. Typically, when present, arsenic and/or phosphorous
are at low concentrations (i.e., less than 5 weight percent). In
certain preferred embodiments, the gallium nitride material has a
high concentration of gallium and includes little or no amounts of
aluminum and/or indium. In high gallium concentration embodiments,
the sum of (x+y) may be less than 0.4, less than 0.2, less than
0.1, or even less. In some cases, it is preferable for the gallium
nitride material layer to have a composition of GaN (i.e., x+y=0).
Gallium nitride materials may be doped n-type or p-type, or may be
intrinsic. Suitable gallium nitride materials have been described
in U.S. patent application Ser. No. 09/736,972, incorporated
herein.
[0074] Gallium nitride material region 14 is of high enough quality
so as to permit the formation of devices therein. Preferably,
gallium nitride material region 14 has a low crack level and a low
defect level. As described above, transition layer 15 may reduce
crack and/or defect formation. In some embodiments, gallium nitride
material region 14 has about 10.sup.9 defects/cm.sup.2. Gallium
nitride materials having low crack levels have been described in
U.S. patent application Ser. No. 09/736,972, referenced above. In
some cases, gallium nitride material region 14 has a crack level of
less than 0.005 .mu.m/.mu.m.sup.2. In some cases, gallium nitride
material has a very low crack level of less than 0.001
.mu.m/.mu.m.sup.2. In certain cases, it may be preferable for
gallium nitride material region 14 to be substantially crack-free
as defined by a crack level of less than 0.0001
.mu.m/.mu.m.sup.2.
[0075] In certain cases, gallium nitride material region 14
includes a layer or layers which have a monocrystalline structure.
In some preferred cases, gallium nitride material region 14
includes one or more layers having a Wurtzite (hexagonal)
structure.
[0076] The thickness of gallium nitride material device region 14
and the number of different layers are dictated, at least in part,
by the requirements of the specific application. At a minimum, the
thickness of gallium nitride material device region 14 is
sufficient to permit formation of the desired device. Gallium
nitride material device region 14 generally has a thickness of
greater than 0.1 micron, though not always. In other cases, gallium
nitride material region 14 has a thickness of greater than 0.5
micron, greater than 0.75 micron, greater than 1.0 microns, greater
than 2.0 microns, or even greater than 5.0 microns.
[0077] When device 10 is a light-emitting device, it may also
include a reflector region 120 (See FIG. 16). Reflector region 120
increases the reflectivity of an interface and typically directs or
steers the light in a desired location or direction within a
light-emitting device. The composition and structural
characteristics (e.g., thickness) of the reflector region may be
selected to reflect the desired wavelength (or range or
wavelengths) of light.
[0078] Reflector region 120 may be a single layer or a series of
layers. In some cases, reflector region 120 comprises a metal. In
other cases, reflector region 120 may comprise a dielectric or
semiconductor material. In these cases, typically, multiple
dielectric or semiconductor material layers are stacked to form the
reflector region. One example of a multi-layer reflector region is
a Distributed Bragg Reflector (DBR). A DBR has at least two layers
of different compositions (e.g., gallium nitride alloys or
oxide-based compounds).
[0079] The location of the reflector region in the device is
selected so as to reflect light in the desired direction.
Typically, the position of the reflector region is selected
relative to the light emitting region(s) of the device. For
example, if it is desired to reflect light in the direction of the
backside of the device, reflector region 120 is preferably located
above an active region (e.g., 97, FIG. 17) in which light is
generated. If it is desired to reflect light in the direction of
the topside of the device, reflector region 120 is preferably
located below the active region (e.g., 97, FIG. 16). In some cases,
such as when the device is a laser, reflector region 120 may
located both above and below an active region. Depending on the
device design, reflector region 120 may be a portion of the gallium
nitride material region 14, or may be located above or below the
gallium nitride material region. As noted above, in some cases,
reflector region 120 may be an electrical contact, though other
types of electrical contacts are not reflector regions. In
embodiments in which the reflector region also functions as an
electrical contact, the reflector region, for example, may be
formed of aluminum, silver or rhodium.
[0080] Device 10 may be formed using known processing techniques.
Transition layer 15 and gallium nitride material device region 14
may be deposited on substrate 12, for example, using metalorganic
chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE),
and hydride vapor phase epitaxy (HVPE), amongst other techniques.
In some cases, an MOCVD process may be preferred. A suitable MOCVD
process to form a compositionally-graded transition layer 15 and
gallium nitride material device region 14 over a silicon substrate
12 has been described in U.S. patent application Ser. No.
09/736,972, referenced above. When gallium nitride material device
region 14 has different layers, in some cases it is preferable to
use a single deposition step (e.g., an MOCVD step) to form the
entire device region 14. When using the single deposition step, the
processing parameters are suitably changed at the appropriate time
to form the different layers. In certain preferred cases, a single
growth step may be used to form transition layer 15 and gallium
nitride material device region 14.
[0081] When present, reflector region 120 may also be formed using
known processing techniques. For example, when the reflector region
comprises a metal, the metal may be sputtered or evaporated. When
the reflector region comprises a series of semiconductor material
layers, the layers may be deposited using metalorganic chemical
vapor deposition (MOCVD), molecular beam epitaxy (MBE), and hydride
vapor phase epitaxy (HVPE), amongst other techniques. When the
reflector region comprises a series of dielectric material layers,
the layers may be deposited by chemical vapor deposition (CVD) or
sputtering.
[0082] In some cases, it may be preferable to grow device region 14
using a lateral epitaxial overgrowth (LEO) technique that involves
growing an underlying gallium nitride layer through mask openings
and then laterally over the mask to form the gallium nitride
material device region, for example, as described in U.S. Pat. No.
6,051,849, which is incorporated herein by reference. In some
cases, it may be preferable to grow device region 14 using a
pendeoepitaxial technique that involves growing sidewalls of
gallium nitride material posts into trenches until growth from
adjacent sidewalls coalesces to form a gallium nitride material
region, for example, as described in U.S. Pat. No. 6,177,688, which
is incorporated herein by reference. In these lateral growth
techniques, gallium nitride material regions with very low defect
densities are achievable. For example, at least a portion of
gallium nitride material region 14 may have a defect density of
less than about 10.sup.5 defects/cm.sup.2.
[0083] Conventional etching techniques may be used to form via 24.
Suitable techniques include wet chemical etching and plasma etching
(i.e., RIE, ICP etching, amongst others). Different etching
techniques may be utilized when etching through different layers of
device 10. For example, a fluorine-based RIE process may be used to
etch through substrate 12 and a chlorine-based RIE process may be
used to etch through gallium nitride device region 14 and/or
transition layer 15. A pre-determined etching time may be used to
form via 24 with the desired dimensions. In other cases, an etch
stop layer (e.g., See 46, FIG. 5), which has a composition that is
not readily etched by the technique being used, may be provided
within device 10 to stop etching so that precise control over the
etching time is not required to form via 24 with desired
dimensions.
[0084] Backside contact 20 and topside contact 16 may be deposited
using known techniques suitable for depositing conducting materials
such as metals. Such techniques include sputtering, electron beam
deposition, and evaporation, amongst others. In some cases, a
series of layers having different metallic compositions are
deposited successively to form contacts 16, 20. In some of these
cases, an annealing technique is used to yield equilibration of the
contact composition. Because backside contact 20 is deposited
within via 24, the deposition technique should be performed in a
manner that provides sufficient coverage within via 24.
[0085] As known in the semiconductor art, multiple device
structures may be formed on the same wafer of substrate material. A
dicing operation, which utilizes a saw, may be used to separate
individual devices from one another. In embodiments using silicon
substrates, devices may be separated in an etching process (e.g.,
wet or dry) which etches through the substrate and layers. This
etching process may use different etch chemistries when etching
through different layers of the structure and substrate. For
example, a fluorine-based gas may be used to etch through the
silicon substrate and a chlorine-based gas may be used to etch
through gallium nitride device region 14 and/or transition layer
15. Separation using an etching process can enable formation of
devices having non-rectangular die shapes (See FIGS. 23C-23K) which
may be advantageous in certain light emitting applications, as
described further below.
[0086] FIG. 2 illustrates device 10a which includes multiple vias
24a, 24b according to another embodiment of the present invention.
A single backside contact 20 is formed in and across both vias 24a,
24b. Using multiple vias 24a, 24b as shown in FIG. 2 may enhance
heat removal, improve light reflection, and increase vertical
conduction. As noted above, device 10a also includes a
compositionally-graded transition layer 15a formed on a constant
composition transition layer 15b. It should be understood that
device 10a is not limited to this transition layer arrangement and
that other transition layer(s) described herein are possible
including a single transition layer.
[0087] FIG. 3 illustrates device 10b including multiple vias 24a,
24b according to another embodiment of the present invention. A
first backside contact 20a is formed in via 24a and a second
backside contact 20b is formed in via 24b. A dielectric layer 31
may be used, for example, to electrically isolate portions of
backside contact 20b to prevent shorting of device 10. Suitable
compositions for dielectric layer 31 include silicon oxide and
silicon nitride. The embodiment of FIG. 3 does not have a topside
contact (16 in FIG. 1). The embodiment of FIG. 3 may be utilized in
cases when it is not desirable to have a topside contact such as
for surface mounted devices.
[0088] It should be understood that the invention also includes
devices having backside vias and backside contacts with other
configurations than those illustrated herein. For example, backside
contact 20 may extend to an active region within gallium nitride
material device region 14, such as a source region or a drain
region. Also, backside contact 20 may extend substantially through
the thickness of the device so that the backside contact also forms
a contact on topside 18 of the device.
[0089] It should also be understood that certain embodiments of the
invention do not include a backside contact 20 as shown in FIG. 13.
Device 110 includes a first topside contact 16d and a second
topside contact 16e. As shown, first topside contact 16d is formed
on a first topside portion 18a of gallium nitride material region
14 and second topside contact 16e is formed on a second topside
portion 18b of the gallium nitride material region, wherein the
first topside portion and the second topside portion are on
different planes. In other cases, first and second topside contacts
are formed on the same plane. It may be advantageous to include
multiple topside contacts and no backside contacts, for example,
when the topside of the device is mounted to a surface (e.g., in
flip-chip embodiments). Also, it may be advantageous to include
multiple topside contacts and no backside contacts in certain light
emitting devices (e.g., LEDs, lasers) when it is desired to emit
light out of the backside of the device. The absence of a backside
contact, and/or any other material, in backside via 24 of device
110 can enhance light emission, amongst other advantages.
[0090] It should be understood that devices of the invention may
include more than two (e.g., three contacts) topside contacts in
certain device configurations (e.g., FETs)
[0091] FIG. 18 illustrates a light-emitting device 124 that
includes a medium 126 comprising phosphor. The medium, for example,
may include phosphor dispersed in epoxy. The phosphor may convert
light generated within the device to light of a different
wavelength. For example, phosphor may be used to convert blue or
UV-light generated within the device to white light. It should be
understood that light emitting device 124 may have any suitable
layer arrangement including layer arrangements of the LED
embodiments described herein
[0092] Any suitable semiconductor device known in the art including
electronic and opto-electronic devices may utilize features of the
invention. In many cases, the device may be formed entirely within
gallium nitride material region 14 (i.e., the only active device
regions are within gallium nitride material region 14). In other
cases, the device is formed only in part within gallium nitride
material region 14 and is also formed in other regions such as
substrate 12.
[0093] Exemplary devices include light emitting devices (such as
laser diodes (LDs) and light emitting diodes (LEDs)), light
detecting devices (such as detectors and sensors), power rectifier
diodes, FETs (e.g., HFETs), Gunn-effect diodes, varactor diodes,
amongst others. Light-emitting devices of the invention may be
designed to emit the desired wavelength of light including visible
light (e.g., blue) and UV-light. As described above, the device may
also include one or more types of phosphor that converts the light
generated within the device to white light. Although certain
figures may illustrate certain types of devices, it should be
understood that the features of these figures may also be used in
other types of devices of the present invention. For example,
though FIGS. 13-20 illustrate light emitting devices, it should be
understood that features of these figures may also be used in light
detecting devices. In such light detecting devices, active region
97 is a light collector region, in contrast to the light generating
region shown in some of these figures.
[0094] FIGS. 4-8 illustrate examples of gallium nitride material
devices according to the invention. It should be understood,
however, that devices having other structures are also within the
scope of the invention.
[0095] FIG. 4 illustrates an exemplary LED 32 according to one
embodiment of the present invention. LED 32 includes gallium
nitride material device region 14 formed on transition layer 15.
Transition layer 15 may be compositionally-graded and is formed on
silicon substrate 12. In the illustrative embodiment, the following
layers comprise gallium nitride material device region 14 in
succession: a silicon-doped GaN layer 34, a silicon-doped
Al.sub.xGa.sub.(1-x)N layer 36 (e.g., containing 0-20% by weight
Al), a GaN/InGaN single or multiple quantum well 38, a
magnesium-doped Al.sub.xGa.sub.(1-x)N layer 40 (e.g., containing
10-20% by weight Al), and a magnesium-doped GaN layer 41. Via 24
extends from backside 22 to a position within GaN layer 34. Topside
contact 16 is formed of a metal on a p-type region and backside
contact 20 is formed of a metal on an n-type region. LED 32 may be
provided as a variety of different structures including: a double
heterostructure (e.g., Al>0% in layer 36), a single
heterostructure (e.g., Al=0% in layer 36), a symmetric structure,
or an asymmetric structure. The LED illustrated in this embodiment
is designed to emit visible light (e.g., blue light). It should be
understood that LEDs having a variety of different structures may
also be provided according to the invention including LEDs that
emit UV light (See FIG. 21).
[0096] FIG. 5 illustrates an exemplary laser diode 42 according to
one embodiment of the present invention. Laser diode 42 includes
gallium nitride material device region 14 formed on transition
layer 15. Transition layer 15 may be compositionally-graded and is
formed on silicon substrate 12. In the illustrative embodiment, the
following layers comprise gallium nitride material device region 14
in succession: a silicon-doped GaN layer 44, a silicon-doped
Al.sub.xGa.sub.(1-x)N layer 46 (e.g., containing 5-30% by weight
Al), a silicon-doped Al.sub.xGa.sub.(1-x)N layer 48 (e.g.,
containing 0-20% by weight Al), a GaN/InGaN single or multiple
quantum well 50, a magnesium-doped Al.sub.xGa.sub.(1-x)N layer 52
(e.g., containing 5-20% by weight Al), a magnesium-doped
Al.sub.xGa.sub.(1-x)N layer 54 (e.g., containing 5-30% by weight
Al), and a magnesium-doped GaN layer 55. Via 24 extends from
backside 22 to Al.sub.xGa.sub.(1-x)N layer 46 which functions as an
etch-stop layer. Topside contact 16 is formed of a p-type metal and
backside contact 20 is formed of an n-type metal. It should be
understood that laser diodes having a variety of different
structures may also be provided.
[0097] FIG. 6 illustrates a power rectifier diode 56 according to
one embodiment of the present invention. Diode 56 includes gallium
nitride material device region 14 formed on transition layer 15.
Transition layer 15 may be compositionally-graded and is formed on
silicon substrate 12. In the illustrative embodiment, the following
layers comprise gallium nitride material device region 14 in
succession: a silicon-doped GaN layer 58 and an intrinsic GaN layer
60. Via 24 extends from backside 22 to a position within GaN layer
58. Topside contact 16 is formed of a rectifying metal and backside
contact 20 is formed of an n-type metal. It should be understood
that diodes having a variety of different structures may also be
provided.
[0098] FIG. 7 illustrates a double-gated HFET 64 according to one
embodiment of the present invention. HFET 64 includes gallium
nitride material device region 14 formed on transition layer 15.
Transition layer 15 may be compositionally-graded and is formed on
silicon substrate 12. In the illustrative embodiment, the following
layers comprise gallium nitride material device region 14 in
succession: an intrinsic GaN layer 66 and an intrinsic AlGaN region
68. Via 24 extends from backside 22 to a position within GaN layer
66. HFET 64 includes a source topside contact 16a, a gate topside
contact 16b, and a drain topside contact 16c. A backside gate
contact 20 is formed within via 24. It should be understood that
HFETs having a variety of different structures may also be provided
including HFETs having a plurality of gates.
[0099] FIG. 8 illustrates an LED 70 including multiple backside
vias 24a, 24b according to another embodiment of the present
invention. LED 70 includes gallium nitride material device region
14 formed on transition layer 15. Transition layer 15 may be
compositionally-graded and is formed on silicon substrate 12. In
the illustrative embodiment, the following layers comprise gallium
nitride material device region 14 in succession: a silicon-doped
GaN layer 72, a silicon-doped Al.sub.xGa.sub.(1-x)N layer 74 (e.g.,
containing 0-20% by weight Al), a GaN/InGaN single or multiple
quantum well 76, a magnesium-doped Al.sub.xGa.sub.(1-x)N layer 78
(e.g., containing 10-20% by weight Al), and a magnesium-doped GaN
layer 80. Via 24a extends from backside 22 to a position within GaN
layer 72 and via 24b extends from backside 22 to a position within
GaN layer 80. An n-type backside contact 20a is formed within via
24a and a p-type backside contact 20b is formed within via 24b. A
dielectric layer 31 isolates portions of p-type backside contact
20b to prevent shorting. It should be understood that LEDs having a
variety of different structures may also be provided.
[0100] FIG. 9 illustrates a device 82 including backside via 24
that is free of an electrical contact according to another
embodiment of the present invention. Device 82 includes gallium
nitride material device region 14 formed on a transition layer 15.
Device may have any suitable layer arrangement including the layer
arrangements (or a portion thereof) of the LED embodiments
described herein. Transition layer 15 can be
compositionally-graded, as described above. Via 24 extends from
backside 22 to transition layer 15, thus, exposing the transition
layer to the environment. An n-type contact 20 is formed on
backside 22.
[0101] FIG. 10 illustrates a device 96 including a backside via 24
having a cross-sectional area that increases in a direction away
from backside 22. Device 96 may have any suitable layer arrangement
including the layer arrangements (or a portion thereof) of the LED
embodiments described herein. In the illustrative embodiment,
device 96 is a light emitting device that includes an active region
97 in which light is generated, though other devices of the
invention may also include a backside via having this shape. This
via shape may enhance internal light reflections (as indicated by
the arrows) and external light extraction from the topside of the
device. In some cases, and as shown, device 96 may be mounted on a
reflective surface 98 to further enhance light reflection and/or a
reflector region 120 may be formed on walls of the via. Reflective
surface 98, for example, may be the surface of a packaging material
or a carrier.
[0102] FIG. 11 illustrates a device 100 according to another
embodiment of the invention. Device 100 includes a number of
contacts 102 formed on the front and back of substrate 12. As
shown, device 100 includes the same layer arrangement as the LED of
FIG. 8, though other suitable layer arrangements are also possible.
LED 100 also includes an n-type contact 104 and a p-type contact
106. A dielectric layer 31 isolates portions of the n-type and
p-type contacts to prevent shorting.
[0103] FIG. 12 illustrates a device 108 according to another
embodiment of the present invention. Device 108 has the same layer
arrangement as the device of FIG. 11 except that, during
processing, the entire substrate has been removed using an etching
step. Other layer arrangements may be used. The entire backside of
transition layer 15, which may be compositionally-graded or have a
constant composition, is exposed to the environment. This
embodiment may be particular useful in order to maximize light
extraction from the device. It should be understood that other
devices of the present invention, including non-light emitting
devices, may also be processed by removing the entire substrate. It
should also be understood that devices which include an exposed
transition layer (e.g., a compositionally-graded transition layer)
may also be used in devices that include two topside contacts, for
example, as shown in FIG. 13. A topside or a backside of device 108
may be mounted on, or bonded to, a carrier (not shown). The
carrier, which may be a wafer (e.g., silicon or GaAs), can provide
support and rigidity for the device that may be desirable in the
absence of the original substrate.
[0104] FIG. 14 illustrates a light emitting device 112 according to
another embodiment of the invention. Device 112 includes an active
region 97 and may have any suitable layer arrangement including the
layer arrangements (or a portion thereof) of the LED embodiments
described herein. Device 112 has two topside contacts 114a, 114b
and no backside contacts. Arrows indicate the direction of light.
The topside contacts also function as reflector regions which
reflect, at least a portion of the light generated in layer 97. In
this embodiment, light is emitted out of the backside of the
device.
[0105] FIG. 15 illustrates a light emitting device 116 according to
another embodiment of the invention. During processing of device,
the substrate has been removed, for example, by an etching step. A
topside or a backside of device 116 may be mounted on, or bonded
to, a carrier (not shown, See FIG. 24) which provides support and
rigidity for the device. In this illustrative embodiment, the
entire backside of a transition layer 15b having a constant
composition (e.g., an intermediate layer of a gallium nitride
alloy, aluminum nitride, or an aluminum nitride alloy) is exposed.
A compositionally-graded transition layer 15a is formed on constant
composition transition layer 15b. It should also be understood
that, in some embodiments, constant composition transition layer
15b is absent (or otherwise positioned) and compositionally-graded
transition layer 15a is exposed. In some cases, a passivating layer
may be formed on transition layer 15b; or, transition layer 15b may
be mounted on the surface of a packaging material. The illustrative
embodiment may be particular useful in order to maximize light
extraction from the device. Device 116 also has two topside
contacts 114a, 114b and no backside contacts. The absence of
backside contacts also enhances light emission. It should be
understood that light emitting device 116 may have any suitable
layer arrangement including the layer arrangements (or a portion
thereof) of the LED embodiments described herein.
[0106] FIG. 16 illustrates a light emitting device 118 according to
another embodiment of the invention that includes reflector region
120 located below the active region 97. Reflector region 120
reflects a substantial portion of the light (indicated by arrows)
emitted from the active region in the direction of the topside of
the device. Therefore, this structure enhances light emission out
of the topside of the device. It should be understood that light
emitting device 116 may have any suitable layer arrangement
including the layer arrangements (or a portion thereof) of the LED
embodiments described herein.
[0107] FIG. 17 illustrates a light emitting device 122 according to
another embodiment of the invention that includes reflector region
120 located above the active region 97. Reflector region 120
reflects a substantial portion of the light (indicated by arrows)
emitted from the light emitting region in the direction of the
backside of the device. Therefore, this structure enhances light
emission out of the backside of the device. It should be understood
that light emitting device 122 may have any suitable layer
arrangement including the layer arrangements (or a portion thereof)
of the LED embodiments described herein.
[0108] FIG. 19 illustrates a light emitting device 130 according to
another embodiment of the invention that includes a first reflector
region 120a formed within via 24. Device 130 has two topside
contacts 114a, 114b. Reflector region 120a may be, for example, a
reflective metal layer. It should be understood that reflector
region 120a is not an electrical contact even when it comprises a
conductive metal because it is not designed to be contacted by a
power source. In the illustrative embodiment, device 130 may
include a second reflector region 120b formed over the via which
may be a Distributed Bragg Reflector (DBR) that includes a number
of semiconductor or dielectric layers. Device 130 includes two
reflector regions to increase the ability of the device to reflect
generated light in the desired direction. It should be understood,
however, that other devices may include only one reflector region
which may be formed within the via or may be formed over the via.
It should be understood that light emitting device 130 may have any
suitable layer arrangement including the layer arrangements (or a
portion thereof) of the LED embodiments described herein.
[0109] FIG. 20 illustrates a light emitting device 136 that has
been flipped during use so that backside 22 faces upward and
topside 18 faces downward. Topside contact 114b also functions as a
reflector region that can upwardly reflect light generated in
region 97. The device also includes a second reflector region 120b
which may be a Distributed Bragg Reflector (DBR) that includes a
number of semiconductor or dielectric layers. Device 136 includes
two reflector regions to increase the ability of the device to
reflect generated light in the desired direction. It should be
understood, however, that other devices may include only one
reflector region which may be an electrical contact (e.g., topside
contact 114b) or a layer(s) within the structure of the device. It
should be understood that light emitting device 136 may have any
suitable layer arrangement including the layer arrangements (or a
portion thereof) of the LED embodiments described herein.
[0110] FIG. 21 illustrates an LED 132 designed to emit ultra-violet
light, for example, having a wavelength between about 200 nm and
about 410 nm. LED 132 includes gallium nitride material device
region 14 formed on transition layer 15. Transition layer 15 may be
compositionally-graded and is formed on silicon substrate 12. In
the illustrative embodiment, the following layers comprise gallium
nitride material device region 14 in succession: a silicon-doped
Al.sub.xGa.sub.(1-x)N layer 134 (e.g., containing 0-100% Al), a
silicon-doped Al.sub.xGa.sub.(1-x)N layer 136 (e.g., containing
20-80% by weight Al), an active region 138, a magnesium-doped
Al.sub.xGa.sub.(1-x)N layer 140 (e.g., containing 20-80% by weight
Al), and a magnesium-doped Al.sub.xGa.sub.(1-x)N layer 141 (e.g.,
containing 0-80% by weight Al). Active region 138 may be a single
or multiple quantum well (e.g., Al.sub.xGa.sub.(1-x)N/GaN,
Al.sub.xGa.sub.(1-x)N/Al.sub.yGa.sub.(1-y)N,
Al.sub.xGa.sub.(1-x)N/Al.sub.yIn.sub.(1-y)N, or
Al.sub.xIn.sub.yGa.sub.(1-x-y)N/Al.sub.aIn.sub.bGa.sub.(1-a-b)N).
In some cases, layers 134, 136, 140, 141 may be superlattices and
may include delta-doped regions to enhance conductivity. Topside
contact 16 is formed of a metal on a p-type region and backside
contact 20 is formed of a metal on an n-type region. It should be
understood that LEDs having a variety of different structures may
also be provided according to the invention including other types
of LEDs that emit UV light and LEDs that emit visible light.
[0111] FIGS. 23A-23K show a series of plane-view cross-sections of
the active regions 97 of a series of opto-electronic devices
according to additional embodiments of the present invention. A
plane-view cross-section is the cross-section of the active region
taken in the plane of the active region (See FIG. 24). Though FIGS.
23A-23K are taken with respect to the active region 97 shown in
FIG. 24, it should be understood that active regions having the
illustrated plane-view cross-sections also may be formed in any
other suitable device structure including the other device
structures described herein.
[0112] As seen in the figures, the devices of the invention may
include active regions having a variety of plane-view
cross-sections that may be designed for specific applications. In
some cases, the plane-view cross-sections are rectangular or square
(FIGS. 23A and 23B). Advantageously, certain embodiments of the
invention, also enables formation of non-rectangular plane-view
cross-sections including circular (FIG. 23C), star-shaped (FIG.
23D), hexagon (FIG. 23E), pentagon (FIG. 23F), octagon (FIG. 23G),
triangular (FIG. 23H), trapezoid (FIG. 23I), diamond (FIG. 23J) and
H-shaped (FIG. 23K), amongst others.
[0113] Active regions having non-rectangular plane-view
cross-sections may improve light extraction over conventional
square or rectangular cross-sections by reducing internal
reflective losses. Advantageously, the shape of the cross-sections
may be tailored for the specific device to optimize light
extraction efficiency. In some embodiments, it may be preferred to
enhance light extraction for the active region to have a
non-rectangular, non-circular plane view cross-section. A variety
of other active region cross-sections may also be utilized in
accordance with the present invention.
[0114] Active regions having non-rectangular plane-view
cross-sections may be formed using an etching process. In some
cases, the etching process used to form the active regions may be
the same etching process used to separate individual devices
processed on the same wafer from one another, as described above.
This etching process may be used to form the active region and
separate devices, for example, when the substrate is silicon
because silicon may be readily etched, in contrast to other types
of substrates (e.g., sapphire and silicon carbide) which typically
require the use of a dicing operation to separate devices. In cases
when the etching process used to form the active region is the same
as the etching process used to separate individual devices
processed on the same wafer, the active region may have the same
plane-view cross-section as other non-active regions on the device
(including other layers and the substrate), as well as the overall
die shape. It should be understood that though the same etching
process is used to form the active region and to separate
individual devices processed on the same wafer, different etching
chemistries may be used at various stages during this process, for
example, to etch through different layers.
[0115] It should be understood that active regions having
non-rectangular plane-view cross-sections may be formed in an
etching process that does not separate individual devices processed
on the same wafer from one another. In these cases, the individual
devices may be separated using conventional dicing steps, for
example, to form devices having a rectangular die shape. In these
cases, the active region may have a non-rectangular plane-view
cross-section, while non-active regions may have a different
plane-view cross-section (including a rectangular plane-view
cross-section).
[0116] FIG. 25 shows a light emitting device 160 according to
another embodiment of the present invention. During processing of
device 160, the substrate has been removed, for example, by an
etching step. In this illustrative embodiment, device 160 includes
a topside contact 16 and a backside contact 20. Topside contact 16
also functions as a reflector region. Backside contact 20 is formed
on a transition layer 15b having a constant composition. A
compositionally-graded transition layer 15a is formed on constant
composition transition layer 15b. Transition layers 15a, 15b are
sufficiently conductive to enable conduction between topside
contact 16 and backside contact 20. In some cases, transition
layers 15a, 15b may be doped to achieve sufficient conductivity. It
should also be understood that, in some embodiments, other
transition layer arrangements are possible including those
described above. In the illustrative embodiment, a topside of the
device is mounted to a carrier 162. Carrier 162, for example, may
be a wafer (e.g., silicon or GaAs). Carrier 162 provides support
and rigidity for the device. It should be understood that in other
embodiments carrier 162 may be mounted on a bottom side of the
device. In other cases, a contact may be formed on the carrier.
[0117] It should be understood that light emitting device 160 may
have any suitable layer arrangement including the layer
arrangements (or a portion thereof) of the LED embodiments
described herein.
[0118] Those skilled in the art would readily appreciate that all
parameters listed herein are meant to be exemplary and that the
actual parameters would depend upon the specific application for
which the semiconductor materials and methods of the invention are
used. It is, therefore, to be understood that the foregoing
embodiments are presented by way of example only and that, within
the scope of the appended claims and equivalents thereto the
invention may be practiced otherwise than as specifically
described.
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