Thermal Soret Diffusion in the Liquid Phase Epitaxial Growth of Binary Iii-V Compounds

The conditions necessary for stable nucleation and growth in the liquid phase epitaxial growth of GaAs and InP are analytically established and, in the former, experimentally confirmed in this research. A transient thermodynamic transport treatment of supersaturated to undersaturated melts, which includes the coupling between solute and heat transport(thermal Soret diffusion), has been solved in closed form. The thermal Soret diffusion effect has been found to be a very important factor for the stabilization of solute transport. For steady-state LPE growth, the thermal Soret diffusion will give rise to a separation effect that forces the steady -state solute concentration to exceed the equilibrium liquidus concentration at a noninteracting interface. This increased concentration, near the growth interface, can cause localized nonuniformities in the melt which leads to terrace, miniscus -line and/or hillock growth morphologies. When nucleation and growth are initiated at near equilibrium liquidus conditions, at the substrate interface with a temperature gradient, meltback and spontaneous nucleation are minimized. To enhance stable uniform growth, the substrate should be brought into contact with the melt at a very critical time, during melt saturation, when the equilibrium liquidus concentration is reached at the noninteracting interface of the slider. The critical melt saturation time for the transient concentration to reach the liquidus concentration at this interface has been analytically determined and experimentally confirmed. In this analysis, the Soret thermal diffusion coefficient has also been evaluated in terms of the solute and solvent masses and the temperature dependence of the solute diffusion coefficient. The critical time determined in this analysis appears to be in close agreement with the experimental results for LPE GaAs. When near steady-state solute transport is achieved at the initiation of growth on the substrate, i.e., the liquidus solute concentration has been reached at the growth interface, reproducible terrace and miniscus -line free growth morphologies, with uniform submicron epitaxial layer thicknesses, are obtained.