Thermal stability and phase transformation of conductive α-(Al0.16Ga0.84)2O3/Ga2O3 heterostructure on sapphire substrates were investigated via in situ high temperature x-ray diffraction, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The conductive α-(Al0.16Ga0.84)2O3/Ga2O3 heterostructure with fluorine (F) doping was grown by mist-chemical vapor deposition on sapphire substrates, achieving a Hall mobility of 28 cm2/(V s). The heterostructure exhibited thermal stability up to ∼550–575 °C before transforming to β-(AlxGa1−x)2O3/Ga2O3. The transformed β-Ga2O3 is mainly polycrystalline rather than a high-quality epitaxial phase. Reciprocal space mapping results reveal that the edge dislocation density remains consistently higher than the screw dislocation density throughout the heating process, indicating that the crystalline imperfection in α-Ga2O3 is dominated by in-plane mosaicity. After the phase transformation from the α phase to the β phase, catastrophic damage to the film and upheaval of the surface were observed by SEM and AFM.
Li et al. (Mon,) studied this question.