Thermodynamic analysis of molecular beam epitaxy of group-III sesquioxides

Abstract

Thermodynamic analyses for the growth of group-III sesquioxides, including α-Al2O3, β-Ga2O3, and c-In2O3, by both ozone and plasma-assisted MBE were performed. In either case, under O-rich conditions, the driving force for III2O3 (III = Al, Ga, In) growth () increased with increasing input partial pressure of the group-III metal (), without generation of metal droplets. Conversely, under group-III-metal-rich conditions, decreased with increasing and/or decreasing input partial pressure of O3 or O. This decrease was caused by the formation of Ga2O or In2O during growth of β-Ga2O3 and c-In2O3. The decrease of was smaller because the equilibrium constant of α-Al2O3 formation reaction was very large. Ga and In droplets formed at low temperatures (<420 °C), whereas Al droplets were formed at high temperatures (<820 °C), and the order that enabled growth at higher temperatures was c-In2O3 < β-Ga2O3 << α-Al2O3.