Si Contamination in Open Flow Quartz Systems for the Growth of GaAs and GaP

Abstract

Silicon contamination of III–V compounds is a potentially serious problem because of silicon's amphoteric behavior and its high affinity for oxygen. A potential source of silicon is fused quartz, which is widely used in systems for the growth of and . Most open growth systems use flowing hydrogen because it is easily purified and it can remove solid gallium sesquioxide from the system. In this paper, calculations are presented for the rates of contamination of liquid gallium with silicon and of flowing mixtures with volatile silicon compounds. Ideal gas behavior and local thermodynamic equilibrium are assumed. It is shown that the contact of Ga or with quartz at normal growth temperatures can lead to significant silicon contamination in very dry systems. In addition, it is found that at 800°C, the pressure of water cannot be controlled below 10⁻⁸ atm for H₂ in contact with and for in contact with , regardless of the initial purity of the H₂. These pressures rise appreciably with increasing temperature. In addition, models are presented for the formation of high concentrations of Si at the substrate‐epitaxial interface and for the formation of precipitates in vapor growth systems. The former has previously been associated with the formation of “ I ” or insulating layers. The calculations show that synthesistype systems should give rise to much less silicon contamination than transport‐type systems, and vapor growth systems using as a transporting agent give rise to nearly negligible Si contamination below 1000°C. Other possible ways to minimize silicon contamination are also discussed.