U.S. patent application number 10/155001 was filed with the patent office on 2003-11-27 for high power, high luminous flux light emitting diode and method of making same.
Invention is credited to Chern, Chyi S., Liu, Heng, Ma, Kevin Y., Ruddy, Eugene J., So, William W., Zhao, Yongsheng.
Application Number | 20030218176 10/155001 |
Document ID | / |
Family ID | 29419595 |
Filed Date | 2003-11-27 |
United States Patent
Application |
20030218176 |
Kind Code |
A1 |
Zhao, Yongsheng ; et
al. |
November 27, 2003 |
HIGH POWER, HIGH LUMINOUS FLUX LIGHT EMITTING DIODE AND METHOD OF
MAKING SAME
Abstract
A high power, high luminous flux light emitting diode (LED)
comprises a substrate, a light-emitting structure, a first
electrode and a second electrode. The LED has a top surface layout
design in which the first electrode has a number of legs extending
in one direction, and the second electrode has a number of legs
extending in the opposite direction. At least portions of the legs
of the first electrode are interspersed with and spaced apart from
portions of the legs of the second electrode. This provides a
configuration that enhances current spreading along the length of
the legs of both electrodes.
Inventors: |
Zhao, Yongsheng; (Monterey
Park, CA) ; So, William W.; (Walnut, CA) ; Ma,
Kevin Y.; (Arcadia, CA) ; Chern, Chyi S.;
(Arcadia, CA) ; Liu, Heng; (Arcadia, CA) ;
Ruddy, Eugene J.; (Claremont, CA) |
Correspondence
Address: |
Jay C. Chiu, Esq.
SONNENSCHEIN NATH & ROSENTHAL
P.O. Box 061080
Wacker Drive Station, Sears Tower
Chicago
IL
60606-1080
US
|
Family ID: |
29419595 |
Appl. No.: |
10/155001 |
Filed: |
May 24, 2002 |
Current U.S.
Class: |
257/81 |
Current CPC
Class: |
H01L 33/20 20130101;
H01L 2933/0016 20130101; H01L 33/38 20130101 |
Class at
Publication: |
257/81 |
International
Class: |
H01L 027/15 |
Claims
What is claimed is:
1. A light-emitting diode comprising: a substrate; a light-emitting
structure disposed above the substrate along a vertical axis, the
light-emitting structure including a first cladding layer and a
second cladding layer; a first electrode in contact with the first
cladding layer of the light-emitting structure, the first electrode
having a leg extending in a first direction along a horizontal axis
perpendicular to the vertical axis; and a second electrode in
contact with the second cladding layer of the light-emitting
structure, the second electrode having at least two legs extending
in a second direction opposite the first direction along the
horizontal axis, a portion of the leg of the first electrode
disposed between and spaced apart from respective portions of the
two legs of the second electrode.
2. The light-emitting diode of claim 1 further comprising a thin
metal layer disposed above the light-emitting structure along the
vertical axis and in contact with the light-emitting structure, the
first electrode extending through the thin metal layer along the
vertical axis to contact the first cladding layer, the first
electrode defining a first elevation along the vertical axis.
3. The light-emitting diode of claim 2, wherein the second
electrode is in contact with a surface of the second cladding layer
in a well formed to expose the surface, the second electrode
defining a second elevation lower than the first elevation along
the vertical axis.
4. The light-emitting diode of claim 1, wherein the first cladding
layer is a P cladding layer and the second cladding layer is an N
cladding layer, and the first electrode is a P electrode and the
second electrode is an N electrode.
5. The light-emitting diode of claim 1, wherein the first cladding
layer is an N cladding layer and the second cladding layer is a P
cladding layer, and the first electrode is an N electrode and the
second electrode is a P electrode.
6. The light-emitting diode of claim 1, wherein the portion of the
leg of the first electrode is spaced apart from one of the portions
of the two legs of the second electrode in substantially equal
distance along the portion of the leg of the first electrode and
the portion of the leg of the second electrode.
7. The light-emitting diode of claim 1, wherein the portions of the
legs of the first and second electrodes are substantially
straight.
8. The light-emitting diode of claim 1, wherein the portion of the
leg of the first electrode is straight and the portions of the legs
of the second electrode are curved.
9. The light-emitting diode of claim 1, wherein the portion of the
leg of the first electrode is straight and the portions of the legs
of the second electrode are angled.
10. The light-emitting diode of claim 1, wherein the second
electrode includes a straight arm that branches into curved
segments, the curved segments including the portions of the two
legs of the second electrode.
11. The light-emitting diode of claim 1, wherein the second
electrode includes a straight arm that branches into angled
segments, the angled segments including the portions of the two
legs of the second electrode.
12. The light-emitting diode of claim 1, wherein the leg of the
first electrode is tapered in the first direction.
13. The light-emitting diode of claim 1, wherein the portions of
the legs of the second electrode are tapered in the second
direction.
14. The light-emitting diode of claim 1, wherein the leg of the
first electrode has an enlarged portion at an end of the leg.
15. The light-emitting diode of claim 14, wherein the enlarged
portion has a circular shape.
16. The light-emitting diode of claim 14, wherein the enlarged
portion has a square shape.
17. The light-emitting diode of claim 14, wherein the leg of the
first electrode further comprises an extension from the enlarged
portion.
18. The light-emitting diode of claim 1, wherein the legs of the
second electrode have enlarged portions at respective ends of the
legs.
19. The light-emitting diode of claim 18, wherein the enlarged
portions have circular shapes.
20. The light-emitting diode of claim 18, wherein the legs of the
second electrode further comprise respective extensions from the
enlarged portions.
21. The light-emitting diode of claim 1, wherein the first
electrode includes two additional outer legs extending in the first
direction, the two legs of the second electrode disposed between
the two outer legs of the first electrode.
22. The light-emitting diode of claim 21, wherein the two outer
legs are substantially straight.
23. The light-emitting diode of claim 22, wherein the two outer
legs each have respective enlarged portions along the leg.
24. The light-emitting diode of claim 23, wherein the enlarged
portions have semicircular shapes.
25. The light-emitting diode of claim 21, wherein the two outer
legs are curved.
26. The light-emitting diode of claim 21, wherein the two outer
legs are angled.
27. The light-emitting diode of claim 21, wherein the two outer
legs are tapered in the first direction.
28. The light-emitting diode of claim 1, further comprises a
reflective layer disposed below the substrate and in connection
with the bottom side of the substrate.
29. The light-emitting diode of claim 1, wherein the leg of the
first electrode and the legs of the second electrode define a
region capable of passing light.
30. The light-emitting diode of claim 29, wherein the region is
substantially in a M shape.
31. The light-emitting diode of claim 29, wherein the region has a
plurality of channels disposed therein, the channels further
dividing the region into sub-regions.
32. The light-emitting diode of claim 31, wherein the sub-regions
are substantially in rectangular shapes.
33. The light-emitting diode of claim 31, wherein at least one of
the channels has a vertical wall.
34. The light-emitting diode of claim 31, wherein at least one of
the channels has an angled wall.
35. A light-emitting diode comprising: a substrate; a reflective
layer disposed below the substrate and in connection with the
bottom side of the substrate; a light-emitting structure disposed
above the substrate along a vertical axis, the light-emitting
structure including a first cladding layer and a second cladding
layer; a thin metal layer disposed above the light-emitting
structure along the vertical axis and in contact with the
light-emitting structure; a first electrode disposed above the
light-emitting structure along the vertical axis, extending through
the thin metal layer along the vertical axis, and in contact with
the first cladding layer of the light-emitting structure, the first
electrode having a plurality of legs extending in a first direction
along a horizontal axis perpendicular to the vertical axis, the
legs being tapered in the first direction; and a second electrode
disposed above an exposed surface of the second cladding layer
along the vertical axis and in contact with the exposed surface,
the second electrode having a plurality of legs extending in a
second direction opposite the first direction along the horizontal
axis, the legs of the second electrode being tapered in the second
direction, the legs of the first electrode interspersed with and
spaced apart from the legs of the second electrode.
36. The light-emitting diode of claim 35, wherein the first
cladding layer is a P cladding layer and the second cladding layer
is an N cladding layer, and the first electrode is a P electrode
and the second electrode is an N electrode.
37. The light-emitting diode of claim 35, wherein the first
cladding layer is an N cladding layer and the second cladding layer
is a P cladding layer, and the first electrode is an N electrode
and the second electrode is a P electrode.
38. The light-emitting diode of claim 35, wherein the first
electrode defines a first elevation, and the second electrode is
disposed in a well, the second electrode defining a second
elevation lower than the first elevation along the vertical
axis.
39. The light-emitting diode of claim 35, wherein the legs of the
first and second electrodes are straight.
40. The light-emitting diode of claim 35, wherein the legs of the
first electrode have enlarged portions at respective ends of the
legs.
41. The light-emitting diode of claim 40, wherein the enlarged
portions have substantially circular shapes.
42. The light-emitting diode of claim 40, wherein at least one of
the legs of the first electrode further comprises a minor extension
extending from the enlarged portion.
43. The light-emitting diode of claim 35, wherein the legs of the
second electrode have enlarged portions at respective ends of the
legs.
44. The light-emitting diode of claim 43, wherein the enlarged
portions have substantially circular shapes.
45. The light-emitting diode of claim 43, wherein at least one of
the legs of the second electrode further comprises a minor
extension extending from the enlarged portion.
46. The light-emitting diode of claim 35, wherein the legs of the
first electrode and the legs of the second electrode define a
surface region capable of passing light.
47. The light-emitting diode of claim 46, wherein the surface
region has a M shape.
48. The light-emitting diode of claim 46, wherein the region has a
plurality of channels disposed therein, the channels further
dividing the region into sub-regions.
49. A light-emitting diode comprising: a substrate; a
light-emitting structure disposed above the substrate along a
vertical axis, the light-emitting structure including a first
cladding layer and a second cladding layer; a thin metal layer
disposed above the light-emitting structure along the vertical axis
and in contact with the light-emitting structure; a first electrode
disposed above the light-emitting structure along the vertical
axis, extending through the thin metal layer along the vertical
axis, and in contact with the first cladding layer of the
light-emitting structure, the first electrode having a plurality of
legs extending in a first direction along a horizontal axis
perpendicular to the vertical axis, at least one leg having an
enlarged portion at its end; and a second electrode disposed above
an exposed surface of the second cladding layer along the vertical
axis and in contact with the exposed surface, the second electrode
having a plurality of legs extending in a second direction opposite
the first direction along the horizontal axis, the legs of the
first electrode interspersed with and spaced apart from the legs of
the second electrode to define a region capable of passing
light.
50. The light-emitting diode of claim 49, wherein the first
cladding layer is a P cladding layer and the second cladding layer
is an N cladding layer, and the first electrode is a P electrode
and the second electrode is an N electrode.
51. The light-emitting diode of claim 49, wherein the first
cladding layer is an N cladding layer and the second cladding layer
is a P cladding layer, and the first electrode is an N electrode
and the second electrode is a P electrode.
52. The light-emitting diode of claim 49, wherein each of the legs
of the first electrode is spaced apart from a respective
neighboring leg of the second electrode in substantially equal
distance along the horizontal axis.
53. The light-emitting diode of claim 49, wherein at least one of
the legs of the first electrode is tapered in the first
direction.
54. The light-emitting diode of claim 49, wherein at least one of
the legs of the second electrode is tapered in the second
direction.
55. The light-emitting diode of claim 49, wherein the enlarged
portion has a substantially circular shape.
56. The light-emitting diode of claim 49, wherein the enlarged
portion has a minor extension extending therefrom.
57. A light-emitting diode comprising: a substrate; a reflective
layer disposed below the substrate and in connection with the
bottom side of the substrate; a light-emitting structure disposed
above the substrate along a vertical axis, the light-emitting
structure including a P cladding layer and an N cladding layer, the
P cladding layer disposed above the N cladding layer along the
vertical axis; a thin metal layer disposed above the P cladding
layer of the light-emitting structure along the vertical axis and
in contact with the P cladding layer; a P electrode disposed above
the P cladding layer of the light-emitting structure along the
vertical axis to define a first elevation, extending through the
thin metal layer along the vertical axis, and in contact with the P
cladding layer, the P electrode having a plurality of legs
extending in a first direction along a horizontal axis
perpendicular to the vertical axis, the legs being tapered in the
first direction and having enlarged regions at respective ends of
the legs; and an N electrode disposed above the N cladding layer of
the light-emitting structure along the vertical axis, the N
electrode in contact with a surface of the N cladding layer in a
well formed to expose the surface, the N electrode defining a
second elevation offset from the first elevation along the vertical
axis, the N electrode having a plurality of legs extending in a
second direction opposite the first direction along the horizontal
axis, the legs of the N electrode being tapered in the second
direction and having enlarged regions at respective ends of the
legs, the legs of the P electrode interspersed with and spaced
apart from the legs of the N electrode.
58. The light-emitting diode of claim 57, wherein the second
elevation is lower than the first elevation.
59. The light-emitting diode of claim 57, wherein the legs of the
first electrode and the legs of the second electrode define a
surface region capable of passing light.
60. The light-emitting diode of claim 59, wherein the surface
region is substantially in a M shape.
61. The light-emitting diode of claim 59, wherein the surface
region has a plurality of channels disposed therein, the channels
further dividing the surface region into sub-regions.
62. The light-emitting diode of claim 61, wherein the sub-regions
are substantially in rectangular shapes.
63. A method of making a light-emitting diode, the method
comprising: providing a substrate; forming a light-emitting
structure above the substrate along a vertical axis, the
light-emitting structure including a first cladding layer and a
second cladding layer; forming a first electrode above the
light-emitting structure along the vertical axis, the first
electrode coupled to the first cladding layer of the light-emitting
structure, the first electrode having a leg extending in a first
direction along a horizontal axis perpendicular to the vertical
axis; and forming a second electrode on an exposed surface of the
second cladding layer, the second electrode having two legs
extending in a second direction opposite the first direction along
the horizontal axis, wherein a portion of the leg of the first
electrode is disposed between and spaced apart from respective
portions of the two legs of the second electrode.
64. The method of claim 63, further comprising forming a thin metal
layer above the light-emitting structure along the vertical axis
and in contact with the light-emitting structure.
65. The method of claim 64, wherein the first electrode extends
through the thin metal layer along the vertical axis to define a
first elevation, and the second electrode defines a second
elevation lower than the first elevation.
66. The method of claim 63, wherein the portion of the leg of the
first electrode is straight, and the portions of the two legs of
the second electrode are at least one of straight, curved and
angled.
67. The method of claim 63, wherein the portion of the leg of the
first electrode is tapered in the first direction.
68. The method of claim 63, wherein the portions of the legs of the
second electrode are tapered in the second direction.
69. The method of claim 63, wherein the leg of the first electrode
has an enlarged portion at end of the leg.
70. The method of claim 63, wherein the legs of the second
electrode have enlarged portions at ends of the legs.
71. The method of claim 63, further comprising forming a plurality
of channels within a surface region defined by the leg of the first
electrode and the legs of the second electrode, the surface region
being divided into sub-regions by-the channels.
72. A method of making a light-emitting diode, the method
comprising: providing a substrate; forming a reflective layer below
the substrate; forming a light-emitting structure above the
substrate along a vertical axis, the light-emitting structure
including a first cladding layer and a second cladding layer;
forming a thin metal layer above the light-emitting structure along
the vertical axis and coupled to the light-emitting structure;
etching the thin metal layer to define a first opening in the thin
metal layer exposing a portion of the first cladding layer of the
light-emitting structure; coupling a first electrode to the first
cladding layer via the first opening, the first electrode
comprising a plurality of legs extending in a first direction along
a horizontal axis perpendicular to the vertical axis; etching the
light-emitting diode to define a second opening exposing a portion
of the second cladding layer of the light-emitting structure; and
coupling a second electrode to the second cladding layer via the
second opening, the second electrode comprising a plurality of legs
extending in a second direction opposite the first direction along
the horizontal axis, the legs of the first electrode interspersed
with and spaced apart from the legs of the second electrode.
73. The method of claim 72, wherein the first electrode defines a
first elevation along the vertical axis, and the second electrode
defines a second elevation, the second elevation being lower than
the first elevation.
74. The method of claim 72, wherein the legs of the first electrode
are at least one of straight, curved and angled, and the legs of
the second electrode are at least one of straight, curved and
angled.
75. The method of claim 72, wherein the legs of the first electrode
are tapered in the first direction.
76. The method of claim 72, wherein the legs of the second
electrode are tapered in the second direction.
77. A plurality of light emitting diodes as disclosed in claim 1,
wherein each of said plurality of light emitting diodes is
positioned in a closed spaced apart relationship to at least one of
said plurality of light emitting diodes.
78. A plurality of light emitting diodes as disclosed in claim 35,
wherein each of said plurality of light emitting diodes is
positioned in a closed spaced apart relationship to at least one of
said plurality of light emitting diodes.
79. A plurality of light emitting diodes as disclosed in claim 57,
wherein each of said plurality of light emitting diodes is
positioned in a closed spaced apart relationship to at least one of
said plurality of light emitting diodes.
Description
FIELD OF INVENTION
[0001] The present invention relates generally to light emitting
devices using compound semiconductor materials. More particularly,
the present invention relates to high power, high luminous flux
light emitting diodes.
BACKGROUND OF INVENTION
[0002] Light emitting diode (LED) technology has revolutionized
lighting equipment in recent years. Due to the advantages offered
by light emitting diodes (LEDs), many applications now incorporate
LEDs instead of conventional incandescent lighting sources. These
applications include, but are not limited to, traffic signaling,
electronic signs, medical applications, instrumentation, and
general illumination. LEDs generally consume much less power as
equally luminous incandescent lamps, and LEDs are also much more
durable than conventional incandescent lighting sources. This leads
to less frequent replacements and lower maintenance costs. Also,
less electrical power consumption by the LEDs translates into less
strain on a power source, such as an alternator or battery. LEDs
are also insensitive to vibration and have lower switch-on time in
comparison to most incandescent lighting sources.
[0003] For LEDs to replace incandescent lighting sources in
applications as described above, the LEDs will have to provide high
luminous output while maintaining reliability, low power
consumption and low manufacturing cost. In many of the
above-described applications, the LEDs are in the form of LED chips
having an edge length of around 300 .mu.m. An individual LED chip
of this type usually has low power output and can only be subjected
to low injection current. As a result, these LED chips need to be
assembled into clusters or arrays to achieve the required luminous
flux level.
[0004] Multiple clusters or arrays of LED chips are generally
mounted onto a board and then integrated with a lamp housing,
electronics, and various lenses. Due to the small size of these LED
chips and the limited amount of luminous flux that each can
generate, the number of LED chips necessary to achieved the
required flux levels is generally quite large. This increases the
complexity in packaging and installing LED chips for a particular
application, in terms of both time and manufacturing cost. For
example, much time and manufacturing cost are needed for mounting,
optical collecting, and focusing the emissions from the LED chips.
Extra time and cost are also required to install and aggregate the
LED chips in a specific arrangement as required by a specific
application.
[0005] Attempts have been made to manufacture LED chips that are
capable of creating higher luminous flux than the .about.300 .mu.m
edge length LED chips. One approach is to increase the edge length
and make each LED chip larger. The larger size allows more current
to flow over and through the LED chip, and higher luminous flux is
generated per LED chip as a result. Although the larger size
simplifies packaging and installation of the LED chips because a
fewer devices are required to be packaged and installed,
reliability and power consumption become problematic. Specifically,
larger size LED chips currently available are limited in their
power and luminous flux output. For example, several commercial
devices currently available are limited to a current dissipation of
approximately 350 mA.
[0006] The primary limiting factor in larger LED chips is the
inability for current to spread evenly over and through the entire
structure of an LED chip. Rather, the current accumulates at
specific spots on the LED chip, preventing the efficient use of the
available light-emitting semi-conductive material. This phenomenon
is commonly referred to as "current crowding." Current crowding
tends to occur at points on electrical contacts of an LED chip
because of the tendency of charge carriers to travel a path of
least resistance. Current crowding may also occur in certain
regions of the electrical contacts depending on the capacity for
each of the regions to accept and spread current. Current crowding
leads to unstable luminous flux output with bright spots and dim
spots on the LED chip. Current crowding also necessitates more
current to be injected into the LED chip, which leads to high power
consumption and can cause breakdown in the LED chip. As a result,
light is not emitted efficiently, and power consumption is not
minimized. Moreover, the larger size LED chips currently available
include additional limiting factors that further contribute to its
limited power and limited luminous flux output. These limiting
factors include ineffective heat dissipation, deficient light
enhancing structure, and limited number of light emitting regions
that results in high light re-absorption within the device
structure. Therefore, high power, high luminous flux LED chips
cannot be achieved using conventional means.
SUMMARY OF INVENTION
[0007] Aspects of the present invention relate to high power, high
luminous flux light emitting diodes and the methods of making them.
In one embodiment, the light-emitting diode comprises a substrate,
a light-emitting structure disposed above the substrate along a
vertical axis, a P electrode having a number of legs extending in
one direction along a substantially horizontal axis perpendicular
to the vertical axis, and an N electrode having a number of legs
extending substantially horizontally in the direction opposite to
the direction of the legs of the P electrode. The light-emitting
structure includes a P cladding layer, an active layer and an N
cladding layer. The P electrode is in contact with the P cladding
layer of the light-emitting structure, while the N electrode is in
contact with the N cladding layer of the light-emitting structure.
The N electrode is disposed at a lower surface than the P
electrode, where the lower surface is defined by a mesa etch
process, forming a mesa edge separating the N electrode from the P
electrode. A thin metal layer is under the P electrode, which is
overlapped and in contact with the P electrode and separated from
the N electrode by the mesa edge. The P and N electrodes are
designed in such a manner that portions of the legs of the P
electrode are interspersed with and spaced apart from portions of
the legs of the N electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 illustrates a top level view of an LED 100
constructed according to an embodiment of the present
invention;
[0009] FIG. 2 illustrates a top level view of an LED 200
constructed according to an embodiment of the present
invention;
[0010] FIG. 3 illustrates a top level view of an LED 300
constructed according to an embodiment of the present
invention;
[0011] FIG. 4 illustrates a top level view of an LED 400
constructed according to an embodiment of the present
invention;
[0012] FIG. 5 shows a cross-sectional side view of an LED 500
constructed according to an embodiment of the present
invention;
[0013] FIG. 6 shows a cross-sectional side view of an LED 600,
showing channels, constructed according to an embodiment of the
present invention;
[0014] FIGS. 7a and 7b illustrate a plurality of LEDs arranged in
exemplary relationships according to embodiments of the present
invention;
[0015] FIG. 8 illustrates a method of making the LED shown in FIG.
1 according to an embodiment of the present invention;
[0016] FIG. 9 illustrates a method of making the LED shown in FIG.
2 according to an embodiment of the present invention; and
[0017] FIG. 10 illustrates a top level view of an LED 1000
constructed according to an embodiment of the present
invention.
DETAILED DESCRIPTION
[0018] FIG. 1 illustrates a top level view of an LED 100
constructed according to an embodiment of the present invention.
The top view of the LED 100 shows an N electrode 110, a P electrode
120, and a region 150 capable of passing light defined by the P
electrode 120 and the N electrode 110. A thin, substantially
translucent metal layer 130 is disposed above the region 150 and
between the N electrode 110 and the P electrode 120, which is
overlapped with the P electrode 120, and separate from the N
electrode 110 by the mesa edge 160. Although the LED 100 is shown
to retain a square shape in the embodiment of FIG. 1, it is noted
that any shape may be employed depending on the specific
application. In one embodiment, the LED 100 is a square and has an
edge length of around 1.20 mm-1.26 mm.
[0019] Although not shown in FIG. 1, disposed below the thin metal
layer 130 and the region 150, along a vertical axis, is a
light-emitting structure with an N cladding layer and a P cladding
layer. The N electrode 110 is in contact with the N cladding layer
at outside of the mesa edge 160, while the P electrode 120 is in
contact with the P cladding layer and overlap with the thin metal
current spreading layer 130. In operation, a voltage difference is
applied between the P electrode 110 and N electrode 120 to activate
the light-emitting structure of the LED 100, and current flows from
the P electrode 110 to the N electrode 120 and the current spreaded
from the P electrode 110 to the thin metal layer 130 diffuses
through the layers of the LED 100. The spreading of the current
from the P electrode 110 to the N electrode 120 is enhanced by the
layout design of and/or specific features on the P and N electrodes
110, 120 as well as the thin metal layer 130. With the current
spread and flowing through the active region of the LED,
recombination of charge carriers occurs resulting in the release of
light energy through the region 150 and out into the
environment.
[0020] In the embodiment, the N electrode 110 has a contact portion
117 and three substantially straight tapered legs 112, 114, 116
extending to the left along a horizontal axis, and the P electrode
has a contact portion 127 and two straight tapered legs 122, 124
extending to the right along the horizontal axis. The two legs 122,
124 of the P electrode 120 are interspersed with and spaced apart
from the three legs 112, 114, 116 of the N electrode 110. As viewed
from above, the legs 112, 114, 116, 112, 124 appear to be parallel
to each other. In this configuration, the leg 122 of the P
electrode 120 is disposed between the legs 112, 114 of the N
electrode 110, while the leg 124 of the P electrode 120 is disposed
between the legs 114, 116 of the N electrode 110. On the other
hand, the leg 114 of the N electrode 110 is disposed between the
legs 122, 124 of the P electrode. Although the P electrode 120 is
shown to have two legs and the N electrode 110 is shown to have
three legs, the placement of the P electrode 120 and the N
electrode 110 may be interchanged according to embodiment of the
present invention. That is, a P electrode would be the right
electrode with three legs and a larger total surface area, while an
N electrode would be the left electrode with two legs and a smaller
total surface area.
[0021] One feature of the embodiment in FIG. 1 is the legs of the N
and P electrodes 110, 120 being tapered, with wide ends being
closer to the electrode contact portions 117, 127 of the N and P
electrodes 110, 120, respectively, and narrow ends being further
away from the electrode contact portions 117, 127 of the N and P
electrodes 110, 120, respectively. In FIG. 1, the legs 122, 124 of
the P electrode 120 are tapered to the right, while the legs 112,
114, 116 of the N electrode 110 are tapered to the left. Because
the tapering in the legs 112, 114, 116 of the N electrode 110 runs
in the opposite direction to the tapering in the legs 122, 124 of
the P electrode 120, the legs 122, 124 of the P electrode 120 taper
off to the right and decrease in width while the legs 112, 114, 116
of the N electrode 110 expand to the right and increase in
width.
[0022] In one embodiment, the decrease in width in the P electrode
legs 122, 124 along the length of said legs in one direction is
proportional to the increase in width in the N electrode legs 112,
114, 116 along the length of said legs in the same direction. Thus,
each of the P electrode legs 122, 124 is spaced apart from its
neighboring N electrode leg in substantially equal distance along
each of the P electrode legs 122, 124 and its neighboring N
electrode leg. For example, in looking at the leg 122 of the P
electrode 120 and the leg 114 of the N electrode 110, the P
electrode leg 122 tapers in direction opposite to that of the N
electrode leg 114. This tapering arrangement allows the narrowing
of the P electrode leg 122 in one direction to be compensated by
the widening of the N electrode leg 114 in the same direction. This
makes the distance between the P electrode leg 122 and the N
electrode leg 114 substantially equal along the length of the two
legs 114, 122, and variations in this distance are minimized. Thus,
when current flows from the P electrode leg 122 through the thin
film 130 to the N electrode leg 114, the current traverses
substantially the same distance along the length of the two legs
and, hence a substantially equally resistive path. This promotes a
uniform current spreading along the length of the two legs 122, 114
in the rectangular shaped region define by the two legs 122,
114.
[0023] The layout design of the P electrode 120 and the N electrode
110 defines the region 150, which substantially retains a M shape
according to the embodiment shown in FIG. 1. In this configuration,
the M shape is rotated 90.degree. clockwise. The region 150 is
capable of passing light produced from the LED 100. The thin metal
layer 130 is formed above the region 150 and disposed between the P
electrode 120 and the N electrode 110. In one embodiment, the thin
metal layer 130 overlaps with the P electrode 120 and separate from
the N electrode 110 by the mesa edge 160. The thin metal layer 130
comprises Nickel and Gold (Ni/Au). Alternatively, other material
that has current spreading characteristics and does not
significantly obstruct light produced from the LED 100 may also be
used.
[0024] The thin metal layer 130 promotes current spreading
therethrough as well as current diffusion down the layers
therebelow. Through the thin metal layer 130, current spreads
initially from the wide end of the P electrode leg 122 to portions
of the region 150 next to the wide end. The wide end provides more
area for the initial high current to start spreading, avoiding
current crowding near the electrode contact portion 127 and the
thin metal layer 130. The current spreads outward to the portion of
the region 150 next to the electrode leg 122 as the current
propagates toward the narrow end of the P electrode leg 122.
Because less and less current is present as the current spreads to
the region 150 along the P electrode leg 122 and propagates toward
the narrow end, the P electrode leg 122 is made narrower. As the
taper progresses along an electrode leg, resistance in the
conductor increases, and less current passes. Consequently, current
escapes from the electrode into the conductive layer substantially
evenly along the edge of the electrode rather than from one point.
This again has the advantage of promoting even current spreading
along the length of the legs of the P and N electrodes. Similarly,
the P electrode leg 122 and the N electrode leg 112 function in
likewise fashion as described above for the P electrode leg 122 and
the N electrode leg 114. An added benefit of making the legs
tapered is to enlarge the region 150, creating extra area for light
to emit from the LED 100. This further improves luminous
efficiency.
[0025] In one embodiment, the leg 114 of the N electrode 110
includes an enlarged portion 115 at its end, while the outer leg
112 of the N electrode 110 includes an enlarged portion 113 toward
the end of the outer leg 112. Similarly, the leg 122 of the P
electrode also includes an enlarged portion 125 and an extension
126 toward the end of the leg 122. In one embodiment, the enlarged
portions 113, 115, 125 encourage current distribution along the
length of their respective legs and toward the legs' respective
narrow ends. This again promotes current spreading and avoids
current crowding in the LED 100. In another embodiment, the
enlarged portions 113, 115, 125 and/or the extension 126 provide
better anchoring of their respective legs by increasing the contact
area between the legs and the layer below. This promotes to
decrease the contact resistance and increase reliability of the
device. Although the enlarged portions 113, 115, 125 are shown to
have either a semicircular or circular shape, it is noted that the
enlarged portions 113, 115, 125 may have another shape, such as a
square, rectangular, triangular and elliptical shape. In other
embodiments, different sizes and different shapes of the enlarged
portions may also be employed in a single LED or among different
LEDS in multiple arrays of LEDs.
[0026] FIG. 2 illustrates a top level view of an LED 200
constructed according to another embodiment of the present
invention. The LED 200 has substantially the same structure as that
of the LED 100. The top view of the LED 200 shows an N electrode
210, a P electrode 220, a region 250 capable of passing light
defined by the P electrode 220 and the N electrode 210, and a
plurality of channels 264 disposed in the region 250. The N
electrode 210 has three straight tapered legs 212, 214, 216
extending to the left, and the P electrode 220 has two straight
tapered legs 222, 224 extending to the right. For illustration
purpose only, the region 250 is shown in black, while the P and N
electrodes 220, 210 and the channels 264 are shown in white. The
two legs 222, 224 of the P electrode 220 are interspersed with and
spaced apart from the three legs 212, 214, 216 of the N electrode
210.
[0027] The region 250 substantially retains an M shape, rotated
90.degree. clockwise, according to the embodiment shown in FIG. 2.
The region 250 is capable of passing light produced from a
light-emitting structure disposed below the surface of the LED 200.
Disposed within the region 250 are a number of channels 264 that
further divide the region 250 into sub-regions. For examples, with
respect to the top portion of the region 250 defined by the P
electrode legs 212, 214 and the N electrode leg 222, the channels
264 divide this portion into six substantially rectangular shaped
sub-regions 251-256. In other embodiments, different shapes may be
employed for the sub-regions. The channels 264 are openings or
trenches within the region 250, and they provide additional surface
area to the region 250 for light to escape. The channels 264 do not
have absorption materials above them to limit light output from the
light-emitting structure. Examples of the absorption materials
include the thin metal layer 230 and the light emitting structure
and P and N electrodes. Thus, light emits from the channels 264 in
a more efficient manner. This improves luminous efficiency of the
LED 200. The channels 264 further minimize contacts between the
sub-regions themselves, allowing current spreading to be focused
within a sub-region, between a respective portion of a leg, of the
P electrode 220 and a respective portion of a leg of the N
electrode 210 of the sub-region.
[0028] In the exemplary configuration shown in FIG. 2, current
spreads from the P electrode leg 222 out toward the sub-regions
251-256 to either the N electrode leg 212 or the N electrode leg
214. The tapering of the P electrode legs 222, 224 along the length
of those legs run opposite to the tapering of the N electrode legs
212, 214, 216 along the length of the N electrode legs 212, 214,
216. The sub-regions 251, 254 are near the wide end of the P
electrode leg 222, while the sub-region 253 is near the wide end of
the N electrode leg 214, and the sub-region 256 is near the wide
end of the N electrode leg 212. As the current comes in from the
wide end of the P electrode leg 222, the current starts spreading
into the region closest to the wide end, i.e., sub-regions 251,
254, and moving toward to the narrow ends of the N electrode legs
212, 214. The current propagates along the length of the P
electrode leg 222, and then current spreading occurs in sub-regions
252, 255. In the same manner, current spreading occurs in
sub-regions 253, 256 when current propagates to the narrow end of
the P electrode leg 222.
[0029] Although not readily shown from the top view of the LED 200,
the channels may have vertical walls or angled walls according to
different embodiments of the present invention. Although the
channels 264 are shown to be straight and either horizontal or
vertical when viewed from above in FIG. 2, it is noted that
channels may retain a different line shape or may be slanted or
curved when viewed from above in other embodiments. The number of
channels may also vary, dividing the region 250 into more or fewer
than the twelve sub-regions shown in FIG. 2. Channels with
different lengths and widths may also be employed in a single LED
or among different LEDS in multiple arrays of LEDs according to
other embodiments.
[0030] FIG. 3 illustrates a top level view of an LED 300
constructed according to an embodiment of the present invention.
The LED 300 has an electrode design of the N and P electrodes that
is different from those illustrated in FIGS. 1 and 2. In the
embodiment, some of the legs of or portions of the legs of the LED
300 are curved, creating a region 350 with rounded portions shown
in FIG. 3. The top view of the LED 300 shows an N electrode 310, a
P electrode 320, and the region 350 capable of passing light
defined by the P electrode 320 and the N electrode 310. The N
electrode 310 has a straight leg 314 and two curved legs 312, 316
extending to the northeast corner, and the P electrode 320 has two
curved segments 322, 324 extending to the southwest corner. In
particular, the P electrode 320 includes a straight arm 325 that
branches into the curved segments 322, 324. For illustration
purpose only, the region 350 is shown in white, while the P and N
electrodes 320, 310 are shown in black. The two segments 322, 324
of the P electrode 320 are interspersed with and spaced apart from
the three legs 312, 314, 316 of the N electrode 310.
[0031] In the embodiment, the leg 314 of the N electrode 310
includes an enlarged portion 315 at its end, which has similar
characteristics as the enlarged portion 115 shown in FIG. 1.
Although the enlarged portion 315 is shown to have a circular
shape, it is noted that another shape may be employed in other
embodiments. Although the legs/segments of the P and N electrodes
320, 310 are not tapered and channels are not provided in the LED
300, legs/segments of an LED with a similar electrode design as
that of the LED 300 may be tapered and/or channels may be provided
according to other embodiments of the present invention.
[0032] FIG. 4 illustrates a top level view of an LED 400
constructed according to an embodiment of the present invention.
The LED 400 presents yet another electrode design of the N and P
electrodes. In the embodiment, some of the legs or portions of the
legs of the LED 400 are angled, creating a region 450 with
triangular portions shown in FIG. 4. The top view of the LED 400
shows an N electrode 410, a P electrode 420, and the region 450
capable of passing light defined by the P electrode 420 and the N
electrode 410. The N electrode 410 has a straight leg 414 and two
angled legs 412, 416 extending to the southwest corner, and the P
electrode 420 has two angled segments 422, 424 extending to the
northeast corner. In particular, the P electrode 420 includes a
straight arm 425 that branches into the angled segments 422, 424.
For illustration purpose only, the region 450 is shown in white,
while the P and N electrodes 420, 410 are shown in black. The two
segments 422, 424 of the P electrode 420 interspersed with and
spaced apart from the three legs 412, 414, 416 of the N electrode
410.
[0033] In the embodiment, the leg 414 of the N electrode 410
includes an enlarged portion 415 at its end, which has similar
characteristics as the enlarged portion 115 shown in FIG. 1.
Although the enlarged portion 415 is shown to have a square shape,
it is noted that another shape may be employed in other
embodiments. Although the legs/segments of the P and N electrodes
420, 410 are not tapered and channels are not provided in the LED
400, legs/segments of an LED with a similar electrode design as
that of the LED 400 may be tapered and/or channels may be provided
according to other embodiments of the present invention.
[0034] FIG. 5 shows a cross-sectional side view of an LED 500
constructed according to an embodiment of the present invention. If
the LED 500 were to represent the LED 200 shown in FIG. 2 or an
embodiment similar to the LED 200 when looking from above, this
cross-sectional side view would represent a view obtained by
cutting across Line A-A shown in FIG. 2. The cross-sectional side
view of the LED 500 shows a substrate 20, a reflective layer 10, a
light-emitting structure 60, a well 80, a thin metal layer 230', a
P electrode 220' and an N electrode 210'. In one embodiment, the
LED 500 is Gallium Nitride (GaN) based, and the substrate 20 is
made of sapphire, silicon carbide, or another suitable crystalline
material. The reflective layer 10 is disposed below the substrate
20 along a vertical axis. The reflective layer 10 reflects light
back toward the top surface, or the emitting surface, of the LED
500. In one embodiment, the reflective layer 10 acts as a mirror
and is made of aluminum. In other embodiments, other types of metal
or material that provides the similar reflective effect may be
utilized. According to an embodiment of the present invention, the
reflective layer 10 is made of material that further provides
thermal benefit to the LED 500 by improving the heat dissipation
capability of the LED 500. In the embodiment, the reflective layer
10 tends to draw heat produced in the LED 500 during operation and
radiate it into the surrounding environment in an efficient
manner.
[0035] The light-emitting structure 60 is disposed above the
substrate 20. In one embodiment, the light-emitting structure 60
comprises an active layer 50 sandwiched in between an N cladding
layer 30 and a P cladding layer 40. In operation, the forward
biasing of the LED 500 causes light 5 to be emitted from the active
layer 50. Light emits in various directions as shown by the arrows
in FIG. 5. Light that travels toward the substrate 20 will be
reflected back by the reflective substrate 10. Within the
light-emitting structure 60, the N cladding layer 30 is disposed
above the substrate 20 along the vertical axis, and the P cladding
layer 40 is disposed above the N cladding layer 30 along the
vertical axis. In one embodiment, the P cladding layer 40 comprises
Aluminum Gallium Nitrite (AlGaN), and the N cladding layer 30
comprises silicon doped Gallium Nitrite (Si:GaN). The P cladding
layer 40 and the N cladding layer 30 form parts of the
light-emitting structure of the LED 500. The thin metal layer 230'
is disposed above the P cladding layer 40 of the light-emitting
structure along the vertical axis and in contact with the P
cladding layer 40. Although the P cladding layer 40 is shown to be
on top of the N cladding layer 30 in LED 500, their positions may
be reversed in other embodiments.
[0036] In the embodiment shown in FIG. 5, the P electrode 220' is
disposed above the P cladding layer 40 of the light-emitting
structure along the vertical axis. Being in contact with the P
cladding layer 40 at one end, the P electrode 220' extends through
the thin metal layer 230' along the vertical axis at the other end.
On the other hand, the N electrode 210' is disposed in the well 80
that has an exposed surface 35 of the N cladding layer 30. The N
electrode 210' is in contact with the surface 35 of the N cladding
layer 30 in the well 80. Because the N electrode 210' is disposed
in the well 80, which is at a lower elevation than the top of the
LED 500, the N electrode 210' is at a lower elevation than the P
electrode 220'. In another embodiment, the location of the P
cladding layer 40 and the P electrode 220' may be switched with
that of the N cladding layer 30 and the N electrode 210',
respectively, making the N electrode 210' be at a higher elevation
than the P electrode 220'. In yet another embodiment, the well 80
is not present, and there is no elevation offset between the P
electrode 220' and the N electrode 210'.
[0037] In one embodiment, the LED 500 may further include other
layers disposed above and/or below the light-emitting structure 60.
These layers, along with the layers shown presently in FIG. 5, may
be grown in a Metal Organic Chemical Vapor Deposition (MOCVD)
reactor. A buffer layer(s) may, for example, be inserted somewhere
between the substrate 20 and the light-emitting structure 60 to
compensate the crystal lattice mismatch between layers and/or to
allow formation of high quality materials at the beginning of
crystal growth of the LED 500. In one embodiment, a window
structure formed of layers of GaN doped with different
concentration of Magnesium may be formed between the light-emitting
structure 60 and the P electrode 220'. In this case, even though
the P electrode 220' is not in direct contact with the P cladding
layer 40, they are still electrically connected with each other.
The precise structure, composition and doping of the additional
layers, as well as the layers presently shown in FIG. 5, are
dependent on the required wavelength of the light-emission to be
generated and need to be appropriately adapted in each individual
case.
[0038] FIG. 6 shows a cross-sectional side view of an LED 600
constructed according to an embodiment of the present invention. In
particular, channels 264" are illustrated in this cross-sectional
side view. If the LED 600 were to represent the LED 200 shown in
FIG. 2 or an embodiment similar to the LED 200 when looking from
above, this cross-sectional side view would represent a view
obtained by cutting across Line B-B shown in FIG. 2. The
cross-sectional side view of the LED 600 shows a substrate 20", a
reflective layer 10", an N cladding layer 30", a P cladding layer
40", a mesa 80", channels 264", a thin metal layer 230", a P
electrode 220" and an N electrode 210". In the embodiment, the
reflective layer 10" is disposed below the substrate 20" along a
vertical axis. The reflective layer 10" reflects light back toward
the top surface, or the side emitting surface, of the LED 600. The
N cladding layer 30" is disposed above the substrate 20", and the P
cladding layer 40" is disposed above the N cladding layer 30". In
operation, the forward biasing of the LED 600 causes light 5" to be
emitted therefrom. In one embodiment, the P cladding layer 40"
comprises AlGaN, and the N cladding layer 30" comprises InGaN. The
thin metal layer 230" is disposed above the P cladding layer 40"
along the vertical axis and in contact with the P cladding layer
40". Although the P cladding layer 40" is shown to be on top of the
N cladding layer 30" in LED 600, their positions may be reversed in
other embodiments.
[0039] In the embodiment shown in FIG. 6, the P electrode 220" is
disposed above the P cladding layer 40" of the light-emitting
structure along the vertical axis. Being in contact with the P
cladding layer 40" at one end, the P electrode 220" extends through
the thin metal layer 230" along the vertical axis at the other end.
On the other hand, the N electrode 210" is disposed in the outside
of mesa 80a" that has an exposed surface 35" of the N cladding
layer 30". The N electrode 210" is in contact with the surface 35"
of the N cladding layer 30" in the outside of mesa 80a", which is
at a lower elevation than the top of the LED 600, the N electrode
210" is at a lower elevation than the P electrode 220". In the
embodiment, a well 80"b is also provided next to the P electrode
220", providing extra opening to the side of the LED 600.
[0040] In one embodiment, the channels 264" cut through the thin
metal layer 230" and the P cladding layer 40" to the N cladding
layer 30", wherein a small portion of the N cladding layer 40" is
also removed. The channels 264" may, for example, have the same
depth as that of the wells 80a", 80b". This allows the channels
264" and the wells 80a", 80b" to be formed together simultaneously
in the same processing steps. The channels 264", which shape
similar to trenches, are openings that provide additional surface
area for light to emit from the LED 600. As compare to light that
exits from the top surface of the LED 600, which must past through
the P cladding layer 40" and the thin metal layer 230", light that
exits from the channels 264" does not have to pass through such
absorbtion material. The wells 80a", 80b" also provide
non-absorbing area for light to exit. The wells 80a", 80b" allow
light to exit from the side, without having to pass through the P
cladding layer 40" or the thin metal layer 230" and the active
layer. Together, the channels 264" and the wells 80a", 80b" further
improve luminous efficiency of the LED 600.
[0041] FIGS. 7a and 7b illustrate a number of LED chips arranged in
exemplary relationships according to embodiments of the present
invention. In these embodiments, a number of LED chips are
assembled into multiple clusters or arrays, which are then mounted
onto a board and then integrated with a lamp housing, electronics,
and/or various lenses to form a product. The LED chips may be
placed in various arrangements, and FIGS. 7a and 7b show two
examples of such arrangements. In FIG. 7a, the LED chips 710-740
are placed edge to edge, essentially forming a bigger
square/rectangle. The wiring 745 provides the required electrical
connection for the LED chips 710-745. In FIG. 7b, the LED chips
750-790 are placed substantially in a cross arrangement. The wiring
795 provides the required electrical connection for the LED chips
750-795. The arrangement of the LED chips is dependent on, for
example, the required light-emission to be generated or the shape
of the housing, and it is appropriately adapted according to
individual cases.
[0042] FIG. 8 illustrates a method of making the LED 100 shown in
FIG. 1 according to an embodiment of the present invention. In step
P800, a substrate is provided. In one embodiment, the substrate
comprises sapphire. In block P810, a light-emitting structure is
formed above the substrate. This includes the formation of a first
cladding layer and a second cladding layer, preferably an N
cladding layer and a P cladding layer, respectively. In one
embodiment, the P cladding layer is formed above the N cladding
layer. In block P820, a thin metal layer is formed above the
light-emitting structure and coupled to the light-emitting
structure.
[0043] In block P830, an opening is created in the thin metal
layer, exposing a portion of the first cladding layer of the
light-emitting structure. In one embodiment, viewed from above, the
opening resembles the U shape of the P electrode shown in FIG. 1,
with two straight tapered opening portions extending to the right
and having enlarged regions toward the ends of the portions. In the
embodiment, the opening is created by conventional masking and
etching techniques. In block P840, another opening, in the form of
a well when viewed from the side of the LED 100, is created. The
well exposes a portion of the second cladding layer of the
light-emitting structure. The surface of the well is at a lower
elevation than the surface of the opening formed in block P830. In
one embodiment, viewed from above, the well resembles the M shape
of the N electrode shown in FIG. 1, with three straight tapered
opening portions extending to the left and having enlarged regions
toward the ends of the portions. In the embodiment, the
opening/well is created by conventional masking and etching
techniques. In block P850, a P electrode is coupled to the first
cladding layer via the opening etched in block P830 and overlap
with the thin metal layer at connection area. In block P860, an N
electrode is coupled to the second cladding layer via the opening,
or the well, etched in block P840.
[0044] In block P870, a reflective layer is disposed below the
substrate. The reflective layer reflects light back toward the top
surface, or the emitting surface, of the LED 100. In one
embodiment, the reflective layer is also made of material that
further provides thermal benefit to the LED 100 by improving the
heat dissipation capability of the LED 100.
[0045] FIG. 9 illustrates a method of making the LED 200 shown in
FIG. 2 according to an embodiment of the present invention. In step
P900, a substrate is provided. In block P910, a light-emitting
structure is formed above the substrate, including the formation of
a P cladding layer, an active layer, and an N cladding layer. In
block P920, a thin metal layer is formed above the light-emitting
structure and coupled to the light-emitting structure. In block
P930, a first opening is created in the thin metal layer, exposing
a portion of the P cladding layer. In one embodiment, viewed from
above, the opening resembles the U shape of the P electrode shown
in FIG. 2, with two straight tapered opening portions extending to
the right and having enlarged regions toward the ends of the
portions.
[0046] In block P940, a second opening, in the form of a well when
viewed from the side of the LED 200, is created. The second opening
exposes a portion of the N cladding layer of the light-emitting
structure. The surface of the well is at a lower elevation than the
surface of the opening formed in block P930. In one embodiment,
viewed from above, the well resembles the M shape of the N
electrode shown in FIG. 1, with three straight tapered opening
portions extending to the left and having enlarged regions toward
the ends of the portions.
[0047] In block P950, a number of straight-line openings, each in
the form of a well when viewed from the side of the LED 200, are
created. In one embodiment, the straight-line openings expose a
portion of the N cladding layer of the light-emitting structure.
The straight-line openings, which may be vertical or horizontal
when viewed from above, serve as the channels of LED 200, dividing
the region defined by the P electrode and the N electrode into
sub-regions. The top surface of the straight-line openings is at a
lower elevation than the surface of the opening formed in block
P930.
[0048] In block P960, an edge opening is formed along the edge of
the LED 200. The fourth opening also represents a well when viewed
from the side of the LED 200. Viewed from above, the edge opening
resembles a hollow square. The top surface of the edge opening is
at a lower elevation than the surface of the opening formed in
block P930. In one embodiment, the openings formed in blocks P950
and P960 have the same depth as the one formed in block P940,
allowing the three openings formed in blocks P940-P960 to be formed
simultaneously during the same etching processes.
[0049] In block P970, a P electrode is coupled to the first
cladding layer via the first opening etched in P930. In block P980,
an N electrode is coupled to the second cladding layer via the
second opening, or the well, etched in P940. The third opening is
left unchanged. In block P990, a reflective layer is disposed below
the substrate to reflect light travels toward it back toward the
top surface, or the emitting surface, of the LED 200.
[0050] FIG. 10 illustrates a top level view of an LED 1000
constructed according to an embodiment of the present invention.
The top view of the LED 1000 shows an N electrode 1100, a P
electrode 1200, and a region 1500 capable of passing light defined
by the P electrode 1200 and the N electrode 1100. A thin,
substantially translucent metal layer 1300 is disposed above the
region 1500 and between the N electrode 1100 and the P electrode
1200, which is overlapped with the P electrode 1200, and separate
from the N electrode 1100 by a mesa edge 1600. Although the LED
1000 is shown to retain a square shape in the embodiment of FIG.
10, it is noted that any shape may be employed depending on the
specific application.
[0051] Although not shown in FIG. 10, disposed below the thin metal
layer 1300 and the region 1500, along a vertical axis, is a
light-emitting structure with an N cladding layer and a P cladding
layer. The N electrode 1100 is in contact with the N cladding
layer, while the P electrode 1200 is in contact with the P cladding
layer and overlaps with the thin metal current spreading layer
1300. The operation of the LED 1000 has been disclosed hereinabove
with respect to similar embodiments and as such shall not be
discussed further herein.
[0052] The spreading of the current from the P electrode 1100 to
the N electrode 1200 is enhanced by the layout design and relative
positioning of the P and N electrodes 1100, 1200 as well as the
thin metal layer 1300.
[0053] In the embodiment depicted in FIG. 10, the N electrode 1100
has a contact portion 1170 and a plurality of legs 1120, 1140, 1160
extending from the contact portion 1170 along a horizontal axis.
The P electrode 1200 has a contact portion 1270 and at least two
legs 1220, 1240 extending from the contact portion 1270 along the
horizontal axis in a direction opposite the plurality of legs 1120,
1140, 1160.
[0054] The at least two legs 1220, 1240 of the P electrode 1200 are
interdigitated with and spaced apart from the three legs 1120,
1140, 1160 of the N electrode 1100. As viewed from above, the legs
1120, 1140, 1160, 1120, 1240 appear to be parallel to each other.
The P electrode 1200 and N electrode 1100 may be interchanged and
the current flow reversed and the LED 1000 will still function.
[0055] Each leg 1120, 1140, 1160, 1220, 1240 has an outer edge as
defined by the periphery thereof. As depicted in FIG. 10, the
minimum distance from the outer edge of any one leg of the N
electrode 1100 to the outer edge of at least one leg of the P
electrode 1200 is substantially the same for all points along the
outer edge of each leg 1120, 1140, 1160, 1220, 1240. External edges
1180 of the N electrode legs 1120, 1140, 1160 that are at the
periphery of the LED 1000 are not considered in determining the
minimum travel distances.
[0056] By maintaining the same minimum distance between the outer
edges of the N and P electrode legs respectively, current crowding
due to differences in resistive distance is minimized and
potentially eliminated.
[0057] Additionally, the spread of current flow through the active
region may be maximized by ensuring that there exists a one to one
correspondence between a point on the outer edge of each leg 1120,
1140, 1160 of the N electrode 1100, and the outer edge of each leg
1220, 1240 of the P electrode 1200, such that current will flow
through the entire region 1500.
[0058] With the electrode designs of the present invention and
specific characteristics, the optical output efficiency or the
luminous efficiency is improved. The LEDs are also able to operate
reliably at its current level while minimizing current crowding.
The specific structures of the elements on the LEDs also allow
emission of light from a number of additional places within the
LEDs. With the reflective layer, the LEDs are also able to have
increased illumination and improved heat dissipation capability.
Embodiments of the present invention are suitable for
implementation in, for example, a large area GaN LED with
dimensions of 0.5 mm.times.0.5 mm to 5 mm.times.5 mm. Embodiments
of the present invention are also suitable for implementation in
applications such as those related to traffic lights, electronic
signs, high power displays, medicine and dentistry.
[0059] It should be emphasized that the above-described embodiments
of the invention are merely possible examples of implementations
set forth for a clear understanding of the principles of the
invention. They are not intended to be exhaustive or to limit the
invention to the precise forms disclosed. Variations and
modifications may be made to the above-described embodiments of the
invention without departing from the spirit and principles of the
invention. All such modifications and variations are intended to be
included herein within the scope of the invention and protected by
the following claims.
* * * * *