Thermodynamic analysis of molecular beam epitaxy of group-III sesquioxides

Abstract Thermodynamic analyses for the growth of group-III sesquioxides, including α -Al 2 O 3 , β -Ga 2 O 3 , and c-In 2 O 3 , by both ozone and plasma-assisted MBE were performed. In either case, under O-rich conditions, the driving force for III 2 O 3 (III = Al, Ga, In) growth ( Δ P III 2 O 3 ) increased with increasing input partial pressure of the group-III metal ( P III o ), without generation of metal droplets. Conversely, under group-III-metal-rich conditions, Δ P III 2 O 3 decreased with increasing P III o and/or decreasing input partial pressure of O 3 or O. This decrease was caused by the formation of Ga 2 O or In 2 O during growth of β -Ga 2 O 3 and c-In 2 O 3 . The decrease of Δ P Al 2 O 3 was smaller because the equilibrium constant of α -Al 2 O 3 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-In 2 O 3 < β -Ga 2 O 3 << α -Al 2 O 3 .