A thermodynamic factor influencing the growth rate and purity of epitaxial layers in the Ga-AsCl3-H2 system

Thermodynamic calculations of the Ga-AsCl₃-H₂ VPE system were expanded to incorporate the incompleteness of the reaction between the source Ga and gas phase. As a result, a saturation temperature was obtained, at which the gas phase reaches equilibrium with the substrate GaAs. The effect of incomplete contact between the gas and the source Ga was taken into account in the calculation by a flow efficiency which defined the hypothetical fraction of the gas which made complete contact with the source Ga. The limitation of the kinetics was described by a reaction efficiency which was incorporated into the reaction constant. The saturation temperature was measured experimentally for two reactors with different geometry. Values of the two efficiencies were derived and their dependence on growth conditions were also examined. The growth rate and undoped impurity level were found to be related in a simpler and perhaps more fundamental way to the saturation temperature than to other growth parameters.