Phase Separation in Indium Gallium Arsenide and Indium Gallium Arsenic Phosphide Epitaxial Films.

Microstructures of InGaAs and InGaAsP epitaxial layers have been investigated to study the phase separation reaction that occurs in these materials. InGaAsP layers have been grown by liquid phase epitaxy on (001), (110), (111), and (123) oriented InP substrates and have been characterized by plan view and cross sectional transmission electron microscopy. Results indicate that the fine scale contrast modulations are two dimensional and lie in the plane of the substrate surface. The crystallographic alignment of these modulations has been shown to be determined by the elastic anisotropy of the substrate crystal in the growth plane. The coarse modulations that are commonly observed in (001) samples are not found in layers grown on the other orientations. It is proposed that the coarse modulations are the result of a buckling reaction which occurs as a result of the fine scale modulations. Representative molecular beam epitaxy and metallorganic chemical vapor deposition grown samples have also been examined and confirm that the LPE results are generic in nature. Annealing studies have also been carried out on phase separated InGaAsP layers to study the reversion phenomenon. The conditions that are required to accomplish homogenization reflect the very slow interdiffusion rates in these materials. Consideration of the annealing results establishes that the rates of mass transfer by bulk diffusion are too low to allow the phase separation reaction to occur by this mechanism. Hall effect measurements show that the carrier mobility increases on annealing and that a concurrent increase in carrier concentration is also observed. Photoluminescence measurements reveal a broadening of the band to band transition peak following the anneal. Finally, the effects of zinc diffusion on phase separated microstructures in InGaAs and InGaAsP layers have also been analyzed. It is shown that the diffusion of zinc into these materials can also homogenize the modulations. For the InGaAs layers it was possible to completely homogenize the microstructure by zinc diffusion, however, for InGaAsP layers only a partial homogenization was accomplished. This model suggests that zinc primarily effects the diffusion of the group III atoms and has very little effect on the diffusivity of the group V constituents. (Abstract shortened with permission of author.).