1987-05-04
1989-04-04
Edlow, Martin H.
357 16, 357 30, H01G 2712
Patent
active
048190365
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to application of a superlattice semiconductor layer to a semiconductor device such as a semiconductor laser, a light emitting diode, a photodiode, an FET and a bipolar transistor, the semiconductor layer being made of a multi-element compound semiconductor which consists of three or less elements and which has an energy band width equivalent in size to a quaternary compound semiconductor.
2. Background Art
By virtue of the development of MOCVD (Metal Organic Chemical Vapor Deposition) and MBE (Molecular Beam Epitaxy), a compound semiconductor device having its thickness controlled so as to be substantially equal to the thickness of a single atom layer has recently been proposed.
One type of semiconductor device which utilizes an energy band width of a multi-element compound consisting of four or more elements has also attracted special interest recently. However, the technique of forming a quaternary compound semiconductor having a film thickness of 100 .ANG. or less, particularly one which consists of two different elements in each of the two different groups e.g., InGaAsP on a III-V group substrate in a lattice matched state still involves many problems in terms of controllability (see H. Kressel et al, "Semiconductor Lasers and Heterojunction LEDs", pp.304 to 318, Academic Press, (1977).
DISCLOSURE OF INVENTION
The symbols III.sup.1, III.sup.2, V.sup.1 and V.sup.2 hereinafter denote, a first III-group element, a second III-group element, a first V-group element and a second V-group element, respectively.
The present inventors have found that a superlattice structure, which consists of a first III-V group (hereinafter referred to as "III.sup.1 -V.sup.1 ") binary crystal layer formed on a III-V group crystal substrate and lattice-matching with the substrate and a III-V group (III.sup.1 -III.sup.2 -V.sup.2) ternary crystal layer composed of two different III-group elements and a V-group element and also lattice-matching with the substrate, is easy to produce and has an average energy band gap (width) equivalent in size to a III14 V group (III.sup.1 -III.sup.2 -V.sup.1 -V.sup.2) quaternary crystal layer. The present inventors have, after further exhaustive study, found that a superlattice structure formed so that the ratio of the film thickness (L.sub.2) of the III.sup.1 -V.sup.1 binary crystal layer and the film thickness (L.sub.3) of the III.sup.1 -III.sup.2 -V.sup.2 ternary crystal layer, i.e., L.sub.2 /L.sub.3, is coincident with a value determined by the calculation described later maintains its lattice-matching state with the substrate even after mixed crystallization spontaneously occurring during growth or mixed crystallization caused by Zn diffusion or Si implantation, and the superlattice structure is thus extremely stable.
More specifically, the feature of the present invention resides in the employment of a superlattice structure composed of (III.sup.1 -V.sup.1) binary and (III.sup.1 -III.sup.2 -V.sup.2) ternary mixed crystals (which lattice-match with a substrate concerned) in place of a (III.sup.1 -III.sup.2 -V.sup.1 -V.sup.2) quaternary crystal layer which is formed on a III-V group binary mixed crystal (III.sup.1 -V.sup.1) such as GaAs and which lattice-matches with the substrate. In other words, the present invention is accomplished on the basis of the following finding. Assuming that either one of the binary and ternary layers which has a smaller energy band gap Eg is referred to as "well" and the other layer, which has a larger energy band gap Eg is referred to as "barrier" and their respective thicknesses are denoted by L.sub.W and L.sub.B, respectively, it is important to adjust the L.sub.W /L.sub.B in advance for a mixed crystal having a metallurgically average composition, which is formed on the assumption that the above-described superlattice structure induces disordering, so that the mixed crystal is also lattice-matched with the previous crystal. It has also been found that, when the L.sub.W /L.sub.B ratio is within
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Kuroda Takao
Matsumura Hiroyoshi
Ohishi Akio
Tsuji Shinji
Watanabe Akiyoshi
Edlow Martin H.
Hitachi , Ltd.
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