Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2002-09-24
2003-09-09
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S697000, C428S220000, C428S336000, C257S079000, C257S094000, C257S103000, C257S013000, C372S043010
Reexamination Certificate
active
06617061
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Group III nitride compound semiconductor device. The present invention is particularly useful for a Group III nitride compound semiconductor device functioning as a light-emitting device such as a light-emitting diode (LED), a laser diode (LD), or the like. Incidentally, the Group III nitride compound semiconductor device is represented by the 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 (each 0<x<1); and quarternary 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, the concept “Group III nitride compound semiconductor” includes a Group III nitride compound semiconductor doped with impurities to form a p-type or an n-type as the conduction type if there is no notice.
The present application is based on Japanese Patent Application No. Hei. 11-353139, which is incorporated herein by reference.
2. Description of the Related Art
The Group III nitride compound semiconductor is a direct transition type semiconductor exhibiting an emission spectrum in a wide range of from ultraviolet to red. The Group III nitride compound semiconductor is applied to a light-emitting device such as a light-emitting diode (LED), a laser diode (LD), or the like. Generally, sapphire is used as a substrate for the Group III nitride compound semiconductor. The Group III nitride compound semiconductor is formed on the substrate. In this case, a so-called clad layer is provided so that electrons from a negative electrode and holes from a positive electrode make pairs in a light-emitting layer. In the Group III nitride compound semiconductor light-emitting device, Al
x
Ga
1-x
N (0<x<1) containing aluminum (Al) is generally used as the clad layer.
FIG. 3
shows a structure of a light-emitting diode (LED)
900
as an example of the background-art Group III nitride compound semiconductor light-emitting device. The light-emitting diode (LED)
900
has a sapphire substrate
901
, and an AlN buffer layer
902
formed on the sapphire substrate
901
.
An n-type layer
903
of GaN doped with silicon (Si), an n-type clad layer
904
of Al
x
Ga
1-x
N doped with silicon (Si), and an active layer
905
of a multiple quantum well structure (MQW) made of an alternate lamination of well layers of Ga
y
In
1-y
N and barrier layers of GaN are formed successively on the buffer layer
902
. A p-type clad layer
906
of Al
x
Ga
1-x
N doped with magnesium (Mg) and a p-type contact layer
907
of GaN doped with magnesium (Mg) are further formed on the active layer
905
. An electrode
908
A is formed on the p-type contact layer
907
. On the other hand, an electrode
908
B is formed on the n-type layer
903
.
In the above background art, however, the n-type and p-type clad layers of Al
x
Ga
1-x
N (0<x<1) are apt to crack because the n-type and p-type clad layers are so thick as to be high in elastic constant. Hence, there is a problem that device characteristic runs short.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a Group III nitride compound semiconductor device and a Group III nitride compound semiconductor light-emitting device in which the elastic constant of thick layers of AlxGa1-xN (0<x<1) is reduced so that lowering of device function is avoided.
In order to achieve the above object, according to an aspect of the present invention, there is provided a Group III nitride compound semiconductor device comprising at least three layers of Al
x
/Ga
1-x
N (0<x<1), and at least three layers of Ga
y
In
1-y
N (0<y<1), wherein the Al
x
Ga
1-x
N layers and the Ga
y
In
1-y
N layers are laminated alternately.
According to another aspect of the present invention, in the above group III nitride compound semiconductor device, each of the layers of Ga
y
In
1-y
N (0<y<1) has a thickness in a range of from 15 nm to 30 nm, inclusively.
According to a further aspect of the present invention, in the above group III nitride compound semiconductor device, the above group III nitride compound semiconductor device is made to be a light-emitting device.
In the Group III nitride compound semiconductor device, a layer requiring a wide band gap demands Al
x
Ga
1-x
N (0<x<1). Therefore, when the layer is formed as a multilayer structure of Al
x
Ga
1-x
N (0<x<1) and Ga
y
In
1-y
N (0<y<1), the layer can be provided as a layer having a wide band gap of Al
x
Ga
1-x
N (0<x<1) and having a small elastic constant as a whole. Hence, cracking caused by the temperature change, or the like, at the time of production and use can be suppressed. This effect is particularly remarkable in a layer of Al
x
Ga
1-x
N (0<x<1) containing a large amount of Al
x
. When a plurality of Al
x
Ga
1-x
N (0<x<1) layers are formed, total characteristic design of the Group III nitride compound semiconductor device, especially design of the light-emitting layer (composition of Al
x
Ga
y
In
1-x-y
N) can be performed more flexibly.
When the thickness of a layer of Ga
y
In
1-y
N (0<y<1) is selected to be in a range of from 15 nm to 30 nm inclusively, cracking can be suppressed approximately perfectly while the function of the layer requiring a wide band gap can be kept high. Incidentally, if the thickness is smaller than 15 nm, the effect of reducing the elastic constant of the laminate of layers of Al
x
Ga
1-x
N (0<x<1) and layers of Ga
y
In
1-y
N (0<y<1) is insufficient. If the thickness is larger than 30 nm, the function of the layer requiring a wide band gap is lowered. The aforementioned device is useful as a light-emitting device such as a laser diode, a light-emitting device, or the like.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.
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patent: 6541798 (2003-04-01), Koike et al.
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Koike Masayoshi
Yamasaki Shiro
McGinn & Gibb PLLC
Stein Stephen
Toyoda Gosei Co,., Ltd.
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