The Ga-As-H-CI vapor phase epitaxial growth system
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I.
INTRODUCTION
THEIII-V compounds like GaAs are gaining in importance as optoelectronic materials, Gallium arsentde Is a direct band gap semiconductor with a high quantum efficiency. Indium phosphide is suitable as a microwave oscillator. For GaAs epitaxial layer preparation, both liqmd phase epitaxlal (LPE) growth and vapor phase epltaxial (VPE) growth techniques are available. Under appropriate conditions, GaAs can be grown from a vapor phase consisting of GaCI, As~. HC1, and H2. Epitaxial InP layers may be grown using the In-PC13-H2 and InP-PC13-H2 vapor phase systems. The present work is concerned with computation of the thermodynamic equilibrium state in vapor phase epitaxial growth systems. The growth (or deposition) rate of the III-V crystals from the vapor phase can be determined, under conditions of virtual equilibrium, from the knowledge of temperature, total pressure, and inlet gas composition, These predicted growth rates are compared with the experimentally measured rates. The GaAs deposition rate data obtained by Shaw ~ with an open tube, chloride transport system are analyzed here in some detail. The results published by Mizuno ~ on the vapor phase growth of InP are being examined similarly and the findings will be reported separately. Models of vapor-phase growth processes involving virtual equilibrium assumption have been developed for typical semiconductor systems and are of considerable theoretical and practical interest. Nagai, 3 Nagai, Shibata. and Okamoto, 4 Rao and L e e ] and Chopper, Hart, and Rao ~ have presented thermodynamic models for the vapor phase growth of the mixed Ga~ Inl _~ As crystals. Using these models, predictions can be made not only of the equilibrium compositions of the gas and solid phases but also of the deposition rates of the solid crystal for a variety of experimental conditions. In this paper, the details of a simple iterative method for calculating the equilibrium compositions in Ga-As-H-C1 vapor phase crystal growth system are presented. The solid phase GaAs(s) that occurs in this sys-
H.G HAN, Graduate Research Assistant, 318 Roberts, FB-10. and Y K. RAO, Professor, Department of Materials Science and Engineering. 323 Roberts, FB-10, are with The Umvers~ty of Washington, Seattle. WA 9'8195. Manuscript submitted April 16, 1984
METALLURGICALTRANSACTIONS B
tern is in its standard state (i.e., at unit chemical activity). The calculation of the rate of deposition 1s performed by the method of the equilibrium extents of reactions m conjunction with the Gauss-Seidel reduction procedure. 7s ~4 The respecnve influences of various experimental variables like temperature, total pressure, and inlet reactant gas composition on the deposition rate are investigated and comparisons made with experimental data.
II.
Ga-As-H-CI SYSTEM
The chemical species which are believed to be present in this system under conditions stmllar to those employed in the epitaxial growth of gallium arsenide are: GaAs(s), GaCI, GaCI~, As~, As> H~_,HCI, and AsH> Inclusion of additional species l
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