Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With heterojunction
Reexamination Certificate
1999-09-21
2001-02-20
Mintel, William (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With heterojunction
C257S096000, C257S097000, C257S103000, C438S093000, C438S094000
Reexamination Certificate
active
06191437
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a semiconductor light emitting device in which a gallium nitride based compound semiconductor layer is provided on a substrate, thereby forming a light emitting diode and a semiconductor laser diode. More particularly, the present invention relates to a semiconductor light emitting device capable of reducing the influence of a shift of a crystal lattice between the substrate and the gallium nitride based compound semiconductor, thereby enhancing light emitting characteristics.
BACKGROUND ART
Conventionally, a semiconductor light emitting device using a gallium nitride based compound semiconductor for emitting blue color type light (yellow from ultraviolet rays), for example, has had a structure shown in FIG.
7
. More specifically, the semiconductor light emitting device comprises a low-temperature buffer layer
22
made of GaN on a sapphire substrate
21
, for example, an n-type layer (a clad layer)
23
in which n-type GaN is epitaxially grown at a high temperature, an active layer
24
formed of a compound semiconductor made of a material for defining a light emitting wavelength to have a smaller band gap energy than the band gap energy of the clad layer, for example, an InGaN based compound semiconductor (which means that a ratio of In to Ga can be variously changed and so is the following), and a p-type layer (a clad layer)
25
including a p-type AlGaN based compound semiconductor layer
25
a
(which means that a ratio of Al to Ga can be variously changed and so is the following) and a GaN layer
25
b
, and a p-side electrode
28
is provided on the surface of the GaN layer
25
b
and an n-side electrode
29
is provided on the surface of the n-type layer
23
which is exposed by etching a part of the provided semiconductor layers. In some cases, the AlGaN based compound semiconductor layer is used on the active layer
23
side of the n-type layer
23
in the same manner as the p-type layer
25
in order to enhance the confinement effects of a carrier.
As described above, the conventional blue color type semiconductor light emitting device using the gallium nitride based compound semiconductor is formed by providing gallium nitride based compound semiconductors such as GaN, InGaN based and AlGaN based compound semiconductors which form a light emitting layer on the sapphire substrate. However, the lattice constant of the sapphire substrate is different from that of the gallium nitride based compound semiconductor by about 16%. Therefore, it is impossible to obtain a gallium nitride based compound semiconductor layer having excellent crystalline properties. In order to solve this problem, a buffer layer such as GaN, AlN or the like which is formed at a low temperature is provided between a single crystal layer of the gallium nitride based compound semiconductor forming a light emitting layer and a substrate, thereby enhancing the crystalline properties of the gallium nitride based compound semiconductor layer as described above.
Although the crystalline properties of the light emitting layer can be improved and the blue color type semiconductor light emitting device can be utilized by providing the above-mentioned buffer layer to be formed at a low temperature, the problem of the crystal defect of the gallium nitride based compound semiconductor layer has not completely been solved. There has been a problem in that a luminance cannot fully be enhanced due to a great leakage current and yield cannot be enhanced due to an insufficient luminance obtained by a slight change in a manufacturing process.
In order to solve the above-mentioned problems, it is an object of the present invention to provide a semiconductor light emitting device having gallium nitride based compound semiconductor layers provided in which crystal defects based on a difference in a lattice constant can be decreased, a leakage current can be reduced and an excellent light emitting efficiency can be obtained.
It is another object of the present invention to provide a method for manufacturing a semiconductor light emitting device in which the crystal defects can be decreased based on the difference in the lattice constant when the gallium nitride based compound semiconductor layers are to be provided.
DISCLOSURE OF THE INVENTION
The present inventors made various investigations in order to decrease crystal defects of semiconductor layers to reduce a leakage current and to enhance a luminance when a light emitting layer forming portion made of gallium nitride based compound semiconductor layers is to be provided. As a result, it has been found that at least one of the gallium nitride based compound semiconductor layers constituting the light emitting layer forming portion is caused to contain oxygen, thereby decreasing a crystal defect density and enhancing a luminance. Moreover, the following has been found. In the case were one semiconductor layer is caused to contain oxygen, it is provided on the underside as much as possible, thereby decreasing the crystal defects of the semiconductor layer provided thereon to enhance a luminance. In the case where a buffer layer made of a gallium nitride based compound semiconductor is provided between the substrate and the light emitting layer forming portion, the crystal defects of the semiconductor layer provided on the buffer layer can be improved even if the buffer layer contains oxygen. Furthermore, it has been found that in the case where the buffer layer is made of AlN, the crystalline properties can be improved even if the AlN is caused to contain oxygen and can be improved still more by causing a plurality of layers to contain oxygen.
The present invention provides a semiconductor light emitting device comprising a substrate, a buffer layer provided on the substrate and made of a gallium nitride based compound semiconductor, and a light emitting layer forming portion in which a gallium nitride based compound semiconductor including an n-type layer and a p-type layer to form a light emitting layer is provided on the buffer layer, wherein the buffer layer or at least one of semiconductor layers constituting the light emitting layer forming portion is a compound semiconductor which contains oxygen in a gallium nitride based compound.
The gallium nitride based compound semiconductor means a semiconductor made of a compound of III group element Ga and V group element N, or a compound obtained by substituting a part of the III group element Ga for another III group element such as Al, In or the like and/or by substituting all or a part of the V group element N for another V group element such as P, As or the like.
The compound semiconductor containing the oxygen is made of Ga
1−x−y
Al
x
In
y
O
z
N
1−z
(0≦x<1, 0≦y<1, 0<z<1). The compound semiconductor containing the oxygen may contain an n-type impurity and/or a p-type impurity. The n-type impurity means at least one kind of Si, Se, Te and the like, and the p-type impurity means at least one kind of Mg, Zn, Be and the like.
Furthermore, the compound semiconductor containing the oxygen is used for the buffer layer, is used for a semiconductor layer on at least the buffer layer side of the light emitting layer forming portion, is used for the active layer interposed between the n-type layer and the p-type layer constituting the light emitting layer forming portion, or is used for two layers or more such as the buffer layer and the semiconductor layer of the light emitting layer forming portion which is in contact with the buffer layer.
More specifically, the substrate is made of a sapphire substrate and the buffer layer is made of GaO
z
N
1−z
(0<z<1), and more specifically, the light emitting layer forming portion has a double heterojunction structure in which the active layer is interposed between an n-type semiconductor layer and a p-type semiconductor layer, and a semiconductor layer which is in contact with at least the buffer layer of the light emitting layer forming portion is made of a GaO
z
N
1−z
(0<z&
Itoh Norikazu
Nakata Shunji
Sonobe Masayuki
Tsutsui Tsuyoshi
Arent Fox Kintner Plotkin & Kahn
Mintel William
Rohm & Co., Ltd.
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