Publications Details

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

Jiang, Kunyao; Tang, Jingyu; House, Stephen D.; Xu, Chengchao; Xiao, Kelly; Porter, Lisa M.; Davis, Robert F.

Ga₂O₃ films were deposited on (100) MgAl₂O₄ spinel substrates at 550, 650, 750, and 850 °C using metal-organic chemical vapor deposition and investigated using x-ray diffraction and transmission electron microscopy. A phase-pure γ-Ga₂O₃-based material having an inverse spinel structure was formed at 850 °C; a mixture of the γ-phase and β-Ga₂O₃ was detected in films grown at 750 °C. Only β-Ga₂O₃ was determined in the films deposited at 650 and 550 °C. A β- to γ-phase transition occurred from the substrate/film interface during growth at 750 °C. The growth and stabilization of the γ-phase at the outset of film growth at 850 °C was affected by the substantial Mg and Al chemical interdiffusion from the MgAl₂O₄ substrate observed in the energy-dispersive x-ray spectrum. Further, atomic-scale investigations via scanning transmission electron microscopy of the films grown at 750 and 850 °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 β-Ga₂O₃ to γ-phase transition and markedly enhances the thermal stability of the latter phase at elevated temperatures.