Gas phase composition and extraneous deposition in GaAs vapor epitaxy

Continuous, in situ rate measurements were used to evaluate the influence of gas phase supersaturation on the GaAs epitaxial growth kinetics relative to the extent of heterogeneous nucleation and extraneous deposition on fused silica. Using a Ga/AsCl 3/H 2 vapor deposition system, the supersaturation was experimentally varied by three techniques: (1) introduction of excess AsCl 3 or HCl to the gas stream leaving the source region, (2) variation of the partial pressure of AsCl 3 entering the source region, and (3) variation of the source temperature. The resulting changes in the relative supersaturation were determined from the temperature at which the epitaxial growth rate is equal to the substrate etch rate. The relative rate of extraneous growth on the fused silica specimen holder was evaluated from the characteristics of gravimetrically measured rate-temperature curves. It is found that additions of excess HCl or variations in the source temperature, while significantly altering the supersaturation, have relatively little effect on suppressing extraneous deposition. On the other hand, dilution of the reactant stream not only reduces the supersaturation, but also greatly suppresses the rate of extraneous deposition relative to epitaxial growth and permits selective epitaxial growth at lower temperatures.