Formation and growth of an amorphous phase by solid-state reaction between GaAs and Co thin films

Abstract

Solid-state amorphization reaction (SSAR) between GaAs and Co thin films was investigated by transmission electron microscopy and Auger electron spectroscopy. Upon annealing of GaAs/Co thin-film couples at 260–300 °C, an amorphous phase was observed to form. Annealing at higher temperatures or for longer times led to the crystallization of the amorphous phase into a supersaturated CoAs solid solution phase with the B31 structure. Amorphization is attributed to the rapid diffusion of Co in the rather open GaAs structure. In order to consider the thermodynamic driving force for amorphization and subsequent crystallization, the phase diagram of CoGa–CoAs was investigated using DTA and metallography. The pseudobinary system was modeled thermodynamically to yield relative stability data for the various phases between GaAs and Co. These data were used to rationalize the amorphization process.