High Electron Mobility in Heteroepitaxial β-Ga₂O₃ and Enhanced Electrical Conductivity in (In_0.5Ga_0.5)₂O₃ by Modifying Donor Energy Levels

As a promising candidate for next-generation electronic devices, Ga₂O₃ still presents challenges, particularly in tailoring its electrical conductivity. In this work, we demonstrate that conductivity in β-Ga₂O₃ heteroepitaxial films can be significantly enhanced by modifying donor energy levels through controlled Si doping and indium alloying. Si-doped Ga₂O₃ and (In_0.5Ga_0.5)₂O₃ thin films were grown on c-plane sapphire substrates using metal-organic chemical vapor deposition (MOCVD), and their structural, optical, and electrical properties were investigated. A high electron mobility of 126 cm²/V s was achieved in Si-doped β-Ga₂O₃, among the highest reported for heteroepitaxial films on sapphire substrate. Hall-effect measurements reveal a large increase in carrier concentration and conductivity at the same Si flow rate for (In_0.5Ga_0.5)₂O₃ despite a mobility reduction to 13.74 cm²/V s due to increased scattering. Cryogenic thermally stimulated photoemission spectroscopy (C-TSPS), developed in-house, reveals that Si doping in (In_0.5Ga_0.5)₂O₃ introduces donors with lower ionization energies compared to Si-doped Ga₂O₃. These shifts in donor energy levels explain the enhanced electrical conductivity observed with the Hall measurement. This study offers new insights into defect-level engineering in β-Ga₂O₃ alloys and establishes a novel pathway to optimize electrical performance in Ga₂O₃-based heterostructures.