【International Papers】Growth and Characterization of Epitaxial Gallium Oxide Films

      Recently, from the Leibniz-Institute for Crystal Growth (IKZ)  have published a dissertation titled“Growth and Characterization of Epitaxial Gallium Oxide Films” in ResearchGate.

Abstract

      The scientific key question of this thesis is to develop the growth processes of MOVPE-grown (100) β-Ga₂O₃ films to fulfill the requirements of vertical devices. An in-depth study has been performed to develop the process of growing μm-level thick films with excellent electrical properties in terms of wide doping range and high mobility. The potential limiting factors and the growth mechanism have been discussed in detail with proposed solutions. The investigations in this thesis can be concluded by the following: (i) For the homoepitaxial growth by MOVPE on (100) β-Ga₂O₃ films up to μm-thickness-level, a certain VI/III (O₂/Ga) ratio is crucial to maintaining the desired step-flow morphology as well as good electrical properties. This observation can be explained by the possible formation of a Ga adlayer on the growing surface, which largely enhances the effective diffusion length of Ga adatoms and screens the Ehrlich-Schwöbel-barrier on the step edge. (ii) For film thicknesses above 1.5 μm, the formation of parasitic particles during the process becomes a serious issue by inducing unwanted structural defects in the film. The pre-reactions in the gas phase have been identified as the source of theses β-Ga₂O₃ particles. By decreasing the showerhead distance to the susceptor and increasing the mixing gas flow in the showerhead, the density of parasitic particles is significantly reduced. Applying this knowledge, for the first time, 4 μm thick MOVPE-grown (100) β-Ga₂O₃ film has been successfully demonstrated with high mobility of up to 160 cm²/Vs at a doping level of ~ 5 × 10¹⁶cm^-3. (iii) Besides the conventional experimental characterization, machine learning as a powerful tool for data analysis has been introduced to dig out more insights from the experimental dataset. Algorithms like Random Forest and its relatives are applied to understand the contribution of growth parameters to the desired physical properties, such as the growth rate and doping level. In addition, the physical meanings behind each growth parameter are revealed. With such a novel approach, a systematic understanding of the growth rate mechanism has been presented, and a competitive Langmuir adsorption model has been suggested to explain the doping behavior of Si-doped β-Ga₂O₃ films grown by MOVPE, leading to a deeper understanding of MOVPE process development.

Paper Link：https://www.researchgate.net/publication/372101459_Growth_and_Characterization_of_Epitaxial_Gallium_Oxide_Films