【Epitaxy Papers】Structural stability of Ga₂O₃ polymorphs on α-Al₂O₃(0001) substrates: Insights from surface and interface energies

      Researchers from Mie University have published a dissertation titled " Structural stability of Ga₂O₃ polymorphs on α-Al₂O₃(0001) substrates: Insights from surface and interface energies " in Journal of Applied Physics.

Abstract

      The structural stability of Ga₂O₃ thin films grown on α-Al₂O₃ (0001) substrates is systematically investigated using density functional theory calculations, with particular emphasis on interfacial energetics, surface stability, and strain relaxation effects. The calculations for α-Ga₂O₃/Al₂O₃ interfaces demonstrate that the α-Ga₂O₃/α-Al₂O₃ interface is energetically more favorable than the corresponding β-phase interface over a wide range of gallium chemical potentials, indicating a strong thermodynamic driving force for α-phase nucleation on sapphire substrates. The influence of lattice mismatch is further examined by considering slip-plane generation. Although strain relaxation reduces elastic energy, the introduction of slip planes increases the interfacial energy, highlighting the competition between strain relief and defect formation. The surface energy calculations reveal that hydroxyl (OH) termination substantially stabilizes α-Ga₂O₃ surfaces, underscoring the importance of surface chemistry under hydroxyl-rich growth environments, such as mist chemical vapor deposition. By combining the calculated interface and surface energies, the free energy of Ga₂O₃ thin films is formulated as a function of film thickness. The analysis shows that the α phase is stabilized in the ultrathin regime due to its lower interface energy, whereas strain relaxation and stability favor the β phase as thickness increases. Surface hydroxylation further modifies the critical thickness for phase transition. These findings provide fundamental insight into phase selection and interfacial stability during Ga₂O₃ heteroepitaxy on α-Al₂O₃(0001) and offer practical guidance for optimizing thin-film growth conditions.

DOI：

https://doi.org/10.1063/5.0338617