Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With heterojunction
Reexamination Certificate
2001-04-20
2002-11-05
Crane, Sara (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With heterojunction
C257S103000, C372S046012
Reexamination Certificate
active
06476421
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light-emitting device having a current diffusion layer and method for manufacture thereof.
In recent years, LEDs (Light-Emitting Diodes), which are semiconductor light-emitting devices, have been in the limelight as indoor/outdoor display devices. In particular, with their trend toward higher brightness, the outdoor display market has been rapidly expanding while LEDs have been growing as a medium to replace neon signs. High-brightness LEDs of visible range in such fields have been developed by AlGaInP-based DH (Double Hetero) type LEDs.
FIGS. 25A
,
25
B,
25
C show a top view, a sectional view and a functional view, respectively, of a yellow-band AlGaInP-based LED as a semiconductor light-emitting device.
In this semiconductor light-emitting device, as shown in
FIGS. 25A and 25B
, an n-GaAs buffer layer
301
(thickness: 0.5 &mgr;m, Si doping: 5×10
17
cm
−3
), an n-AlGaInP cladding layer
302
(thickness: 1.0 &mgr;m, Si doping: 5×10
17
cm
−3
), an undoped (Al
0.3
Ga
0.7
)
0.5
In
0.5
P active layer
303
(thickness: 0.6 &mgr;m), a p-AlGaInP cladding layer
304
(thickness: 0.7 &mgr;m, Zn doping: 5×10
17
cm
−3
), a p-AlGaAs current diffusion layer
305
(thickness: 6 &mgr;m, Zn doping: 3×10
18
cm
−3
), and a p-GaAs cap layer
306
(thickness: 0.1 &mgr;m, Zn doping: 3×10
18
cm
−3
) are grown on an n-GaAs substrate
310
by MOCVD process, and a first electrode
311
is formed on the substrate side while a second electrode
312
is formed on the grown layer side. Regions of the p-GaAs cap layer
306
other than a device center region thereof opposed to the grown-layer side second electrode
312
have been removed. In this semiconductor light-emitting device, having a pn junction formed within the active layer
303
, light emission is generated by recombination of electrons and holes. With this semiconductor light-emitting device molded into 5 mm dia. resin, when a 20 mA current was passed therethrough, the resultant emission intensity was 1.5 cd.
In this semiconductor light-emitting device, as shown in
FIG. 25C
, a current injected from the grown-layer side second electrode
312
expands within the p-AlGaAs current diffusion layer
305
, being injected into the active layer
303
, where most part of the current flows to the region under the second electrode
312
. As a result, light emission over the region under the second electrode
312
is intercepted by the second electrode
312
so as not to go outside, resulting in an ineffective current. This leads to a problem that the emission intensity would be lower.
Thus, as an solution to this problem, there has been proposed a structure in which a current blocking layer for blocking the current is introduced under the second electrode
312
.
FIGS. 26A-26C
show a top view, a sectional view and a functional view, respectively, of a semiconductor light-emitting device having the structure in which the current blocking layer is introduced. In this semiconductor light-emitting device, as shown in
FIGS. 26A and 26B
, an n-GaAs buffer layer
321
(thickness: 0.5 &mgr;m, Si doping: 5×10
17
cm
−3
), an n-AlGaInP cladding layer
322
(thickness: 1.0 &mgr;m, Si doping: 5×10
17
cm
−3
), an undoped (Al
0.3
Ga
0.7
)
0.5
In
0.5
P active layer
323
(thickness: 0.6 &mgr;m), a p-AlGaInP cladding layer
324
(thickness: 0.7 &mgr;m, Zn doping: 5×10
17
cm
−3
), a p-AlGaInP intermediate band gap layer
325
(thickness: 0.15 &mgr;m, Zn doping: 2×10
18
cm
−3
), a p-GaP first current diffusion layer
326
(thickness: 1.5 &mgr;m, Zn doping: 1×10
18
cm
−3
), an n-GaP current blocking layer
327
(thickness: 0.4 &mgr;m, Si doping: 3×10
18
cm
−3
), and a p-GaP second current blocking layer
328
(thickness: 6 &mgr;m, Zn doping: 2×10
18
cm
−3
) are grown on an n-GaAs substrate
330
by MOCVD process, and a first electrode
331
is formed on the substrate side while a second electrode
332
is formed on the grown layer side.
In this semiconductor light-emitting device, the n-GaP current blocking layer
327
is subjected to etching removal with its device center region left, and the second current diffusion layer
328
is re-grown thereon.
In this semiconductor light-emitting device, as shown in
FIG. 26C
, a current injected from the grown-layer side second electrode
332
, avoiding the n-GaP current blocking layer
327
provided under the second electrode
332
, flows to both sides of the n-GaP current blocking layer
327
. As a result, as compared with the semiconductor light-emitting device shown in
FIG. 25
, this semiconductor light-emitting device involves less ineffective current that flows to under the second electrode
332
, resulting in increased emission intensity. With this semiconductor light-emitting device applied to a 5 mm dia. molded article, the emission intensity at a 20 mA current conduction was 2.0 cd, an increase of slightly more than 30% as compared with the semiconductor light-emitting device shown in FIG.
25
. However, because the thickness of the p-GaP first current diffusion layer
326
provided under the n-GaP current blocking layer
327
is as thick as 1.5 &mgr;m, there is still a sneak current going to under the n-GaP current blocking layer
327
as shown in FIG.
26
C. Thus, there is a problem that the ineffective current is not eliminated completely.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a semiconductor light-emitting device, as well as a method for manufacture thereof, which can be reduced in ineffective current with a simple construction and can effectively take out light to outside.
In order to achieve the above object, there is provided a semiconductor light-emitting device comprising: a first-conductive-type first cladding layer, a first-conductive-type or second-conductive-type or an undoped active layer, a second-conductive-type second cladding layer, a second-conductive-type intermediate band gap layer and a second-conductive-type current diffusion layer, all of which are stacked on one side of a surface of a first-conductive-type semiconductor substrate, a first electrode formed on the other side of the surface of the first-conductive-type semiconductor substrate, and a second electrode formed partly on the second-conductive-type current diffusion layer, wherein
a region of the second-conductive-type intermediate band gap layer just under the second electrode is removed, and the second-conductive-type current diffusion layer is stacked in the removal region on the second-conductive-type second cladding layer, and wherein
a junction plane of the second-conductive-type current diffusion layer and the second-conductive-type second cladding layer has an energy band structure of type II.
With this semiconductor light-emitting device having the above constitution, in the removal region of the second-conductive-type intermediate band gap layer, since the junction plane of the second-conductive-type current diffusion layer and the second-conductive-type second cladding layer becomes high in resistance due to the energy band structure of type II, the current flows to around the removal region, allowing ineffective currents flowing under the second electrode formed partly on the second-conductive-type current diffusion layer to be reduced so that the emission intensity is enhanced. It is noted that the first electrode formed on the other side of the surface of the first-conductive-type semiconductor substrate may be either a partial electrode or a full electrode.
Also, there is provided a semiconductor light-emitting device comprising: a first-conductive-type first cladding layer, a first-conductive-type or second-conductive-type or an undoped active layer, a second-conductive-type second cladding layer, a second-conductive-type intermediate band gap layer and a second-conductive-type current diffusion layer, all of which are stacked on one side of
Nakamura Jun-ichi
Ohyama Shouichi
Sasaki Kazuaki
Crane Sara
Nixon & Vanderhye P.C.
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