Mg and Al-induced phase transformation and stabilization of Ga₂O₃-based -phase spinels

Ga2O3 films were deposited on (100) MgAl2O4 spinel substrates at 550, 650, 750, and 850 degrees C using metal-organic chemical vapor deposition and investigated using x-ray diffraction and transmission electron microscopy. A phase-pure gamma-Ga2O3-based material having an inverse spinel structure was formed at 850 degrees C; a mixture of the gamma-phase and beta-Ga2O3 was detected in films grown at 750 degrees C: Only beta-Ga2O3 was determined in the films deposited at 650 and 550 degrees C. A beta- to gamma-phase transition occurred from the substrate/film interface during growth at 750 degrees C. The growth and stabilization of the c-phase at the outset of film growth at 850 degrees C was affected by the substantial Mg and Al chemical interdiffusion from the MgAl2O4 substrate observed in the energy-dispersive x-ray spectrum. Atomic-scale investigations via scanning transmission electron microscopy of the films grown at 750 and 850 degrees C revealed a strong tetrahedral site preference for Ga and an octahedral site preference for Mg and Al. It is postulated that the occupation of these atoms in these particular sites drives the beta-Ga2O3 to c-phase transition and markedly enhances the thermal stability of the latter phase at elevated temperatures.