Active solid-state devices (e.g. – transistors – solid-state diode – Physical configuration of semiconductor – With specified crystal plane or axis
Patent
1994-09-13
1996-10-29
Limanek, Robert P.
Active solid-state devices (e.g., transistors, solid-state diode
Physical configuration of semiconductor
With specified crystal plane or axis
257628, 257190, 257192, H01L 2904
Patent
active
055699545
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an epitaxial substrate of a compound semiconductor comprising a gallium arsenide (hereinafter sometimes referred to as GaAs) single crystal substrate having formed thereon a compound semiconductor epitaxial layer by epitaxial vapor phase growth.
BACKGROUND OF THE INVENTION
The field of various electronic devices using semiconductors has been and will be achieving rapid development. For the time being, silicon is used as a main semiconductor substrate. In recent years, compound semiconductors showing high-speed properties, such as GaAs, have been steadily developed.
Various semiconductor devices endowed with desired performance properties are generally obtained by forming a crystal layer having necessary characteristics on a single crystal substrate by various techniques, such as ion implantation, diffusion, and epitaxial growth. Above all, epitaxial growth has been spreading because it enables not only control of the amount of an impurity but control of the crystal composition or thickness over an extremely broad range and with high precision.
Known methods for epitaxial growth include liquid phase epitaxy, vapor phase epitaxy, and molecular beam epitaxy (hereinafter sometimes abbreviated as MBE), one of vacuum evaporation. Vapor phase epitaxy among them is capable of processing a large quantity of substrates under control and is therefore widely employed on an industrial scale. In particular, metalorganic chemical vapor deposition (hereinafter sometimes abbreviated as MOCVD), which comprises vaporizing an organometallic compound or a metal hydride of an atomic species that is to constitute an epitaxial layer and thermally decomposing the vapor on a substrate to cause crystal growth, has recently been extending its use on account of its applicability to a wide range of materials and suitability for precise control of crystal composition and thickness.
For example, a high electron mobility transistor, sometimes called a modulation doped transistor (MODFET) or a hetero-junction field effect transistor (HJFET), hereinafter inclusively referred to as HEMT, is one kind of field effect transistors (FET) and is of importance as an element of low noise amplifiers in microwave communication systems. The crystal used in HEMT is prepared by making a GaAs crystal and an AlGaAs crystal having necessary electronic characteristics successively grow in a necessary structure on a GaAs substrate by the above-mentioned vapor phase growth.
Crystals for semiconductor lasers, typical light-emitting devices, are also prepared in a similar manner, i.e., GaAs and AlGaAs layers endowed with necessary electrical characteristics, composition and thickness are made to grow on a substrate.
GaAs and an AlGaAs series are widely employed as materials for preparation of these devices since the lattice constant of the latter can be made to agree with that of the former at an arbitrary composition and can achieve various hetero-junctions while maintaining satisfactory crystal characteristics. It is also possible to laminate such a crystal layer as Al.sub.x (In.sub.y Ga.sub.(1-y)).sub.(1-x) P (0<x<, 0<y<1) or In.sub.x Ga.sub.(1-x) As.sub.y P.sub.(1-y) (0<x<l, 0<y<1) by selecting an appropriate composition range so as to match its lattice constant to that of GaAs.
Substrates whose plane azimuth is a {100} plane or its equivalent are generally used in various electron devices, such as the above-described field effect transistors and semiconductor lasers. However, in vapor phase epitaxy by MOCVD as illustrative above, a so-called off-azimuth substrate, which does not have an accurate {100} plane but a plane whose normal is slightly slanted from a <100> direction, is generally used.
There are several reasons for the use of an off azimuth substrate. For example, Uchida, et al. mention that the surface defect density and uniformity of a crystal layer can be improved by slanting a {100} plane to one of the <100> directions included in the {100} plane at an angle
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Fukuhara Noboru
Hata Masahiko
Inui Katsumi
Takata Hiroaki
Hardy David B.
Limanek Robert P.
Sumitomo Chemical Company Limited
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