Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With heterojunction
Reexamination Certificate
2000-11-30
2003-02-11
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With heterojunction
C257S103000, C372S044010
Reexamination Certificate
active
06518599
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a light emitting device using a group III nitride group compound semiconductor. In particular, the present invention relates to a light emitting device using a group III nitride group compound semiconductor in which a stack is formed on an upper surface of a group III nitride group compound semiconductor layer by epitaxial lateral overgrowth (ELO). The group III nitride group compound semiconductor layer comprises regions with many defects and regions with less defects. A group III nitride compound semiconductor can be made of binary compounds such as AlN, GaN or InN, ternary compounds such as Al
x
Ga
1−x
N, Al
x
In
1−x
N or Ga
x
In
1−x
N where (0<x<1), or quaternary compounds Al
x
Ga
y
In
1−x−y
N where (0<x<1, 0<y<1, 0<x+y<1), that is, those are represented by a general formula Al
x
Ga
y
In
1−x−y
N where (0≦x≦1,0≦y≦1,0≦x+y≦1). In accordance with present invention, a group III nitride group compound semiconductor includes a group III nitride group compound semiconductor which is doped with impurities to have p-type or n-type conductivity.
BACKGROUND OF THE INVENTION
A group III nitride group compound semiconductor is a direct-transition-type semiconductor having a wide emission spectrum range from ultraviolet to red, and is applied to light-emitting devices such as light-emitting diodes (LEDs) and laser diodes. The group III nitride group compound semiconductor is, in general, formed on a sapphire substrate. A laser diode, in general, comprises a guide layer and a cladding layer, which are formed on an n-type and a p-type semiconductor side of an active layer, respectively, sandwiching the same. The cladding layer is formed to have a large band gap and is generally made of Al
x
Ga
1−x
N where (0<x<1) including aluminum (Al), such that electrons and holes injected from negative and positive electrodes generate electron-hole pairs in the active layer. The guide layer has a little wider band gap than the active layer. The guide layer is made of, for example, gallium nitride (GaN) such that laser lights can be confined in the active layer by difference of refractive indices. The active layer preferably has a multiple quantum well (MQW) structure.
FIG. 6
illustrates the structure of a laser diode
900
having a conventional group III nitride group compound semiconductor light-emitting device. The laser diode
900
comprises a saphire substrate
91
, and an AlN buffer layer
92
formed thereon.
On the buffer layer
92
, four layers are formed successively: an n-layer
93
made of silicon (Si) doped GaN; an n-cladding layer
94
made of silicon (Si) doped Al
0.08
Ga
0.92
N; an n-guide layer
95
made of silicon (Si) doped GaN; and an active layer
96
having a multiple quantum well (MQW) structure in which a barrier layer made of GaN and a well layer made of Ga
0.85
In
0.15
N are laminated together. On the active layer
96
, a p-guide layer
97
made of magnesium (Mg) doped GaN, a p-cladding layer
98
made of magnesium (Mg) doped Al
0.08
Ga
0.92
N, and a p-contact layer
99
made of magnesium (Mg) doped GaN are formed. An electrode
910
is formed on the p-contact layer
99
and another electrode
911
is formed on a portion of the n-layer
93
.
FIG. 7
is a schematic view of the laser diode
900
. Rd represents a stack and Mrr represents a stack facet. Generally the stacks are formed by etching. The stack facets of several adjacent stacks form a cavity.
In the above-described conventional technique, however, when a layer of a group III nitride group compound semiconductor is formed on a sapphire substrate, dislocations are generated in the semiconductor layer due to a misfit between lattice constants of sapphire and the group III nitride compound semiconductor, which results in degraded device characteristics. In particular, the dislocations due to the misfit are feedthrough dislocations which penetrate the semiconductor layer in a longitudinal direction (a direction vertical to the surface of the substrate), resulting in propagation of about 10
9
cm
−2
of dislocation in the group III nitride group compound semiconductor. The dislocations are then propagated to the uppermost layer of the group III nitride group compound semiconductor layers each having different composition. When stack facets Mrr in
FIG. 7
are formed by etching, ruggedness shown by &phgr; in
FIG. 8
is generated on the stack facets Mrr due to feedthrough dislocations. The ruggedness &phgr; is about 20 nm in depth and formed in cylindrical pattern. Accordingly, the stack facets of the conventional laser diode
900
are remarkably far from ideal stack facets, which have a specular surface having no ruggedness. As a result, the oscillation efficiency of laser reflection becomes remarkably worse.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a light emitting device that overcomes the above-identified deficiencies.
It is another object of the present invention to provide a light emitting device using a group III nitride group compound semiconductor which comprises stack or resonator facets having less ruggedness.
It is another object of the present invention to provide a light emitting device having a group III nitride group compound semiconductor layer having a plurality of distinct regions having many defects and a plurality of distinct regions having less defects.
It is another object of the present invention to provide a light emitting device having a group III nitride group compound semiconductor layer having a plurality of distinct regions having many defects and a plurality of distinct regions having less defects, wherein the stack facets of a stack are arranged in an area having less defects.
It is another object of the present invention to provide a light emitting device using a group III nitride group compound semiconductor that efficiently suppreses feedthrough dislocations that are transmitted to the substrate in vertical direction.
These and other objects of the present invention will apparent in view of the description of the present invention and claims set forth below.
SUMMARY OF THE INVENTION
The present invention is directed to a light emitting device using a group III nitride group compound semiconductor comprising a group III nitride group compound semiconductor and a stack which is formed on the upper surface of a group III nitride group compound semiconductor layer comprising regions with many defects or less defects. The stack is formed so as to traverse the regions of the group III nitride group compound semiconductor layer with many defects and less defects and a stack facet is formed on the region of the group III nitride group compound semiconductor layer with less defects. The stack is formed by employing a process, e.g., cleaving or etching the laminated group III nitride group compound semiconductor layer.
In accordance with the present invention, the light emitting device may include a plurality of stacks which form cavities. The stacks may be formed by etching. It is contemplated that the light emitting device may be a laser diode or a light emitting diode.
In accordance with the present invention, the regions of the group III nitride group compound semiconductor layer with many defects and those regions with less defects are formed in a striped pattern at least near the stack facets. Here a striped pattern does not necessarily represents a rectangular with a short edge and a long edge. It is adequate if each boundaries between the regions of the group III nitride group compound semiconductor with many defects and less defects, which are placed near the stack facets, is a straight line and almost parallel to each other. Boundaries may not be necessarily observed by an apparatus but may be recognizable in a manufacturing process as a divided line that divides the regions with many defects and less defects.
In accordance with the present invention, the stack facets may be parallel to the b
Hiramatsu Toshio
Koike Masayoshi
Tezen Yuta
Umezaki Tamiyo
Crane Sara
Toyoda Gosei Co,., Ltd.
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