Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2000-10-16
2003-10-07
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
Reexamination Certificate
active
06631149
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser diode using group III nitride group compound semiconductor. Here a group III nitride group compound semiconductor is represented by a general formula Al
x
Ga
y
In
1−x−y
N (0≦x≦1, 0≦y≦1, 0≦x+y≦1), which includes binary compounds such as AlN, GaN and InN, ternary compounds such as Al
x
Ga
1−x
N, Al
x
In
1−x
N and Ga
x
In
1−x
N (0<x<1), and quaternary compounds such as Al
x
Ga
y
In
1−x−y
N (0<x<1, 0<y<1, 0<x+y<1). In this specification, 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.
2. Description of the Related Art
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 (LDs). 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 (0<x<1) including aluminum (Al), in order that electrons and holes injected from the negative and the positive electrode, respectively, form electron-hole pairs in the active layer. The guide layer preferably has a wider band gap than the active layer. The guide layer is preferably made of, e.g., gallium nitride (GaN) in order that laser light can be confined in the active layer by total internal reflection due to the difference in refractive indices. The active layer preferably has a multiple quantum well (MQW) structure.
FIG. 5
illustrates the structure of a laser diode (LD)
900
as a conventional group III nitride group compound semiconductor light-emitting device. The laser diode (LD)
900
comprises a substrate
901
, and an AlN buffer layer
902
is formed thereon.
On the buffer layer
902
, the following four layers are formed successively: an n-layer
903
made of silicon (Si) doped GaN; an n-cladding layer
904
made of silicon (Si) doped Al
x
Ga
1−x
N; an n-guide layer
905
made of silicon (Si) doped GaN; and an active layer
906
having a multiple quantum well (MQW) structure in which a barrier layer made of GaN and a well layer made of Ga
1−y
In
y
N are laminated alternately. On the active layer
906
, a p-guide layer
907
made of magnesium (Mg) doped GaN, a p-cladding layer
908
made of magnesium (Mg) doped Al
x
Ga
1−x
N, and a p-contact layer
909
made of magnesium (Mg) doped GaN are formed. An electrode
910
A is formed on the p-contact layer
909
and another electrode
910
B is formed on a portion of the n-layer
903
.
In the above-described conventional technique, however, stress between the sapphire substrate
901
and the n-layer
903
or the n-cladding layer
904
is applied to the active layer
906
through the n-guide layer
905
. As a result, luminous efficiency of the active layer
906
decreases and oscillation threshold current of the laser increases.
SUMMARY OF THE INVENTION
An object of the present invention is, therefore, to provide a laser diode using group III nitride group compound semiconductor, which has a guide layer with decreased elastic constant.
To achieve the above object, and others, a first aspect of the present invention provides a laser diode using a group III nitride group compound semiconductor diode. The diode comprises a guide layer having a multiple layer structure including an indium nitride (InN) layer and is formed on a substrate side of an active layer.
A second aspect of the present invention provides a diode having a guide layer which has a multiple layer structure including an indium nitride (InN) layer which is disposed on the side of the active layer opposite to the substrate.
A laser diode using a group III nitride group compound semiconductor comprises a substrate and group III nitride group compound semiconductor layers laminated thereon. By forming a guide layer which has a multiple layer structure including an indium nitride (InN) layer and has a sufficiently lowered elastic constant beneath an active layer, the elastic constant of the guide layer becomes comparatively smaller. As a result, transmission of stress, which is generated by temperature variation during manufacture or use, can be prevented. When a guide layer which comprises a multiple layers including indium nitride (InN) is also formed on an active layer opposite to the substrate side, further improvement can be obtained. Because of the structure of the emission layer, the laser diode of the present invention can be used to produce ultraviolet light. The guide layers are preferably the multiple layers including InN and a group III nitride group compound semiconductor including no indium (In), for example, Al
x
Ga
1−x
N (0≦x≦1). For example, the guide layers preferably comprise the multiple layers including InN and Al
x
Ga
1−x
N (0<x<1) or, InN and GaN.
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Koike Masayoshi
Tezen Yuta
McGinn & Gibb PLLC
Menefee James
Toyoda Gosei Co,., Ltd.
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