【International Papers】Nucleation Window of Ga₂O₃ and In₂O₃ for Molecular Beam Epitaxy on (0001) Al₂O₂

      The research team from the University of Bremen has published a dissertation titled "Nucleation Window of Ga₂O₃ and In₂O₃ for Molecular Beam Epitaxy on (0001) Al₂O₃" in the scientific journal "ACS Publications".

Abstract

      The epitaxial growth of Ga₂O₃ and In₂O₃ on (0001)-oriented Al₂O₃ by plasma-assisted molecular beam epitaxy is investigated. The synthesis of both materials underlies similar growth kinetics, with the formation of volatile suboxides limiting their growth in the metal-rich regime. Quantitative analysis of β-Ga₂O₃ and c-In₂O₃ growth kinetics has been performed on appropriate buffer layers mimicking homoepitaxial growth conditions. In particular, we investigate the influence of the amount of supplied atomic oxygen on the growth kinetics of β-Ga₂O₃. Considering the heteroepitaxial growth on bare (0001) Al₂O₃, we found that the observed nucleation window is much more limited than the expected growth window derived from homoepitaxial growth conditions. For Ga₂O₃ this was studied in detail and the upper limit of the nucleation window was determined in terms of the gallium to oxygen ratio on the growth surface and the growth temperature. Outside the nucleation window, we report that three monolayers α-(Al_0.75±0.04Ga_0.25∓0.04)₂O₃ formed in the initial stage of growth passivate the surface with respect to further β-Ga₂O₃ nucleation. We attribute the formation of this layer to the intermixing of a Ga-rich adlayer and Al atoms from the substrate until the solubility limit in the α-phase is reached. The observation is accompanied by a specific RHEED pattern with satellite reflexes assigned to a surface reconstruction in the metal-rich growth regime.

Figure S1: AFM images of the β-Ga₂O₃ buffer layer (a) and of a sample showing partial growth with focus on the transition from the nucleation to the non-nucleation regime (b).

Figure S2: RHEED images of the β-Ga₂O₃ buffer layer taken after the growth along the [102] (a) and the [010] (b) azimuth.

Paper Link：https://doi.org/10.1021/acs.cgd.3c00193