Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – Plural fluid growth steps with intervening diverse operation
Reexamination Certificate
2001-12-03
2002-10-29
Chaudhuri, Olik (Department: 2813)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
Plural fluid growth steps with intervening diverse operation
C438S046000, C117S089000, C117S104000
Reexamination Certificate
active
06472298
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a Group III-V compound semiconductor, a method of manufacturing the same, and a light emitting element.
2. Description of the Background Art
Group III-V compound semiconductors, which are expressed by the following general formula In
x
Ga
y
Al
z
N (x+y+z=1, 0≦x<1, 0<y≦1, 0≦z<1), are known as a material for a light emitting element such as a light emitting diode which emits ultraviolet light or blue light and a laser diode which emits ultraviolet light or blue light. Hereafter, x, y and z in the above mentioned general formula will be stated as In concentration, Ga concentration and Al concentration, respectively. Those in which the In concentration is 10% or more, in particular, are important for the purpose of display, since an emission wavelength in a visible range can be adjusted in accordance with the concentration of In.
However, big problems as described below have been impeding efforts to develop light emitting elements which use Group III-V compound semiconductors into a practical use. That is, first, no appropriate substrate has been found which can be used for growing crystal of a Group III-V compound semiconductor, and second, thermal stability of a Group III-V compound semiconductor is not excellent. Now, a detailed description will be given on these points.
Describing the first problem, despite the efforts to grow a Group III-V compound semiconductor on various substrates such as a sapphire substrate, a GaAs substrate and a ZnO substrate, since these substrates have largely different lattice constants and chemical characteristics from the Group III-V compound semiconductor, crystal of a sufficiently high quality has not been produced yet. To deal with this, an approach has been proposed which requires to grow GaN crystal which has a similar lattice constant and chemical characteristics to a Group III-V compound semiconductor first, and thereafter to grow a Group III-V compound semiconductor on the GaN crystal, so as to obtain excellent crystal (Japanese Examined Patent Publication No. 55-3834). However, it is known that a difference in lattice constant between the Group III-V compound semiconductor and GaN becomes larger as the In concentration increases, so that the crystal perfection deteriorates and the number of defects increases, even in this approach. Thus, it is difficult to manufacture a Group III-V compound semiconductor which has a high quality and a high In concentration.
Secondly, it is known that such compound semiconductors which contain In have substantially low decomposition temperatures than such compound semiconductors which do not contain In. For example, while GaN, AlN and mixed crystal of the two are relatively stable at a temperature of 1,000° C. or higher, the thermal decomposition temperature of InN is about 600° C. Although it depends on the In concentration, the compound semiconductors which contain In cause crystal deterioration at a temperature exceeding 1,000° C. and create an increased number of defects, in general.
On the other hand, it is necessary to dispose a p-type current injection layer and an n-type current injection layer on both sides of an active layer to manufacture a light emitting element which is driven at a low voltage. As known in the art, while a compound semiconductor of n-type is easily manufactured, a compound semiconductor of p-type is very difficult to manufacture.
Further, to realize a high p-type conductivity, it is sometimes effective to perform post processing, such as thermal annealing or electron beam irradiation, on a layer which is doped with acceptor type impurities. In general, such processing is likely to be very effective when the layer which is doped with acceptor type impurities is exposed to a surface. Hence, it is preferable to grow the p-type current injection layer after forming the active layer. In addition, it is known that compound semiconductors which do not contain In more easily exhibit p-type conductivity than compound semiconductors which contain In.
For this reason, Ga
x″
Al
y″
N (x″+y″=1, 0<x″≦1, 0≦y″<1) which does not contain In is used as the p-type current injection layer. However, to obtain Ga
x″
Al
y″
N which exhibits excellent p-type conductivity, it is necessary to grow Ga
x″
Al
y″
N at a temperature exceeding 1,000° C. Hence, while Ga
x″
Al
y″
N of p-type is grown at a temperature exceeding 1,000° C., the active layer which contains In is deteriorated.
SUMMARY OF THE INVENTION
An object of the present invention is to obtain a Group III-V compound semiconductor which has a high quality and less defects, to obtain a method of manufacturing the same in which after an In containing layer is grown, GaAlN doped with p-type impurities is grown at a temperature exceeding 1,000° C., without deteriorating the In containing layer, so that a resultant Group III-V compound semiconductor exhibits an excellent emission characteristic, and further, to obtain a light emitting elements using such a Group III-V compound semiconductor which exhibits an excellent emission characteristic.
As a result of a wide range of study on Group III-V compound semiconductors, the inventors of the present invention have found that Group III-V compound semiconductor crystal which has a high quality and less defects is obtained if a Group III-V compound semiconductor has a specific laminated structure and if a Group III-V compound semiconductor which is expressed by a general formula In
x
Ga
y
Al
z
N (x+y+z=1, 0<x<1, 0<y<1, 0≦z<1), is a specific thin layer, and that the thermal stability of the compound semiconductors is improved if a GaAlN layer is grown at a relatively low temperature as a protection layer after a layer which contains In is grown.
That is, the present invention is directed to [1] a Group III-V compound semiconductor having a structure in which a first-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula In
x
Ga
y
Al
z
N (x+y+z=1, 0<x<1, 0<y<1, 0≦z<1), a second-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula Ga
x′
Al
y′
N (x′+y′=1, 0<x′≦1, 0≦y′<1), and a third-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula Ga
a″
Al
y″
N (x″+y″=1, 0<x″≦1, 0≦y″<1), are stacked one atop the other in this order, and in which the first-layer has a thickness in the range between 5 Å and 90 Å.
The present invention is also directed to [2] a Group III-V compound semiconductor having a structure in which a fifth-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula Ga
a
Al
b
N (a+b=1, 0≦a≦1, 0≦b≦1), and a first-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula In
x
Ga
y
Al
z
N (x+y+z=1, 0<x<1, 0<y<1, 0≦z<1), are stacked one atop the other in this order, and in which the first-layer has a thickness in the range between 5 Å and 90 Å.
The present invention is also directed to [3] a Group III-V compound semiconductor having a structure in which a fifth-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula G
a
&Al
b
N (a+b=1, 0≦a≦1, 0≦b≦1), a fourth-layer having a lower impurity concentration than the fifth-layer, which is formed by a Group III-V compound semiconductor which is expressed by a general formula Ga
a′
Al
b′
N (a′+b′=1, 0≦a′≦1, 0≦b′≦1), and a first-layer, which is formed by a Group III-V compound semiconductor
Iyechika Yasushi
Ono Yoshinobu
Takada Tomoyuki
Birch & Stewart Kolasch & Birch, LLP
Chaudhuri Olik
Kielin Erik
Sumitomo Chemical Company Limited
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