Active solid-state devices (e.g. – transistors – solid-state diode – Including semiconductor material other than silicon or... – Group iii-v compound
Reexamination Certificate
2000-05-19
2003-09-09
Smith, Matthew (Department: 2825)
Active solid-state devices (e.g., transistors, solid-state diode
Including semiconductor material other than silicon or...
Group iii-v compound
C438S483000, C438S932000, C438S481000, C117S902000
Reexamination Certificate
active
06617668
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to methods and devices using a group III nitride compound semiconductor represented by a general formula Al
x
Ga
y
In
1-x-y
N (0≦x≦1, 0≦y≦1, 0≦x+y≦1). In particular, the present invention is directed to methods and devices using a group III nitride compound semiconductor which has a substrate comprising silicon (Si). A group III nitride compound semiconductor layer comprises binary compounds such as AlN, GaN, and InN. A group III nitride compound semiconductor layer also comprises 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 a group III nitride compound semiconductor layer further comprises quaternary compounds such as Al
x
Ga
y
In
1-x-y
N (0<x<1, 0<y<1, 0<x+y<1).
2. Description of the Related Art
A group III nitride 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). Group III nitride compound semiconductors are, in general, formed on a sapphire substrate.
However, in the above-described conventional technique, when a layer of a group III nitride compound semiconductor is formed on a sapphire substrate, cracks and/or warpage may be generated in the semiconductor layer. These flaws form due to differences in thermal expansion coefficients between the sapphire substrate and the group III nitride compound semiconductor. As a consequence, dislocations are generated in the semiconductor layer due to misfit, resulting in degraded device characteristics. Further, because sapphire has an insulation characteristic, both positive and negative electrodes need to be formed on the same side of the sapphire substrate, resulting in limitation of miniaturizing the device and degraded manufacturing efficiency. Moreover, because the substrate and the semiconductor layer are made of different materials, the conventional laser diodes have difficulty in obtaining a good cleavage.
SUMMARY OF THE INVENTION
Accordingly, in light of the above problems, an object of the present invention is to realize an efficient method capable of forming a layer of a group III nitride compound semiconductor represented by a general formula Al
x
Ga
y
In
1-x-y
N (0≦x≦1, 0≦y≦1, 0≦x+y≦1) on a silicon substrate, thereby to improve device characteristics. Another object of the present invention is to obtain the optimum surface orientation of the silicon substrate and the optimum orientation for epitaxial growth when the layer of a group III nitride compound semiconductor is formed on the silicon substrate by using epitaxial growth.
In order to solve above and other problems, in a first aspect, the present invention is a device using a group III nitride compound semiconductor comprising: a silicon (Si) substrate; a layer which is formed on (111) plane of the silicon substrate such that substrate-exposed portions are formed in a scattered manner and on which a group III nitride compound semiconductor does not grow epitaxially; and a second layer which grows epitaxially on substrate-exposed portions, or the regions which are not covered by the first layer, and which grows epitaxially on the regions which are covered by the first layer in lateral direction.
The lateral direction, as used in the specification, refers to a direction parallel to a surface of the substrate (surface direction). The second layer comprising a group III nitride compound semiconductor represented by a general formula Al
x
Ga
y
In
1-x-y
N (0≦x≦1, 0≦y≦1, 0≦x+y≦1) does not grow epitaxially on the first layer, and the layer formed on the substrate-exposed portions grows epitaxially on the first layer in lateral direction. Dislocations due to misfit between the silicon substrate and the group III nitride compound semiconductor grow in longitudinal direction, but they hardly grow in lateral direction. Consequently, a crystallinity of the group III nitride compound semiconductor formed on the first layer can be improved. In addition, since there are no chemical junctions between the first layer and the group III nitride compound semiconductor thereabove, the second layer causes neither warpage nor distortions which would otherwise be caused by stress in the layer.
In a second aspect, the present invention is a device using group III nitride compound semiconductor comprising: a silicon (Si) substrate; a first layer which is formed on (111) plane of the silicon substrate and made of a group III nitride compound semiconductor; a second layer which is formed on the first layer such that the first layer-exposed portions are formed in a scattered manner and on which a group III nitride compound semiconductor does not grow epitaxially; and a third layer which grows epitaxially on the third layer-exposed portions, or the regions which are not covered by the second layer, and which grows epitaxially on the regions which are covered by the second layer in lateral direction.
The third layer comprising a group III nitride compound semiconductor represented by a general formula Al
x
Ga
y
In
1-x-y
N (0≦x≦1, 0≦y≦1, 0≦x+y≦1) is formed on an exposed portion of the first layer comprising a group III nitride compound semiconductor 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 serves as a nucleus, as in the first aspect of the present invention. Because crystal growth of the third layer is carried out not on the silicon substrate but on a substrate having the same or similar compositions to those of the third layer, crystallinity of the third layer can be improved. Here similar compositions as used in the specification refers to close lattice constants. The reference also includes the difference of composition ratios of Al, Ga and In (including 0) in the group III nitride compound semiconductor represented by a general formula Al
x
Ga
y
In
1-x-y
N (0≦x≦1, 0≦y≦1, 0≦x+y≦1).
In a third aspect, the present invention forms the first layer to have two-layer structure, comprising a layer made of Al
x
Ga
1-x
N (0<x≦1) and a layer made of a group III nitride compound semiconductor formed thereabove. By forming the first layer, a group III nitride compound including aluminum (Al) can be formed on the silicon substrate in an excellent condition, and a group III nitride compound semiconductor of improved crystallinity can be obtained on the group III nitride compound semiconductor layer.
In a fourth aspect of the present invention, the first layer is formed in a striped pattern. In a fifth aspect of the present invention, the exposed portions formed on (111) plane of the silicon substrate or the upper surface of the third layer are longer in an axis direction which is perpendicular to <110> direction of the silicon substrate. In short, the first layer is formed so that the exposed portions become longer in a direction which is perpendicular to <110> direction of the silicon substrate. The second layer is formed on (111) plane of the substrate or on the third layer. Because the crystal structure of the second layer is affected by (111) plane of the silicon substrate, it can optimize the direction of epitaxial lateral growth of the second layer. Here <110> direction represents [110], [011] and [101] axes directions.
In a sixth aspect of the present invention, the first layer is formed using silicon oxide (SiO
2
). In this case, the second layer is formed by using a group III nitride compound semiconductor which does not include aluminum (Al), and the second layer does not grow epitaxially on the first layer but grows epitaxially in lateral direction. As a result, crystallinity of the second layer can be improved.
In a seventh aspect of the present invention, the first layer is formed using metals of high melting point or an amorphous
Kato Hisaki
Koide Norikatsu
McGinn & Gibb PLLC
Smith Matthew
Toyoda Gosei Co,., Ltd.
Yeusikov V.
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