Microscopic origin of dopant-dependent defect states and carrier compensation in Si- and Sn-doped <b> <i>β</i> </b> -Ga2O3

This work reports a systematic investigation of the defect states and carrier compensation mechanisms in Si- and Sn-doped β-Ga2O3 using hybrid density functional theory calculations combined with high-resolution photoemission spectroscopy. The calculations show that Si introduces a shallower donor level ε(0/+1) ≈ 0.17 eV than does Sn (≈0.23 eV). The deeper donor level in Sn results from the stabilization of neutral SnGa via Sn 4d–O 2p hybridization. At higher doping levels, gallium vacancies (VGa) act as the dominant acceptor-type defects. Notably, Sn exhibits a strong tendency to form split-vacancy complexes (Snic-2VGa), with formation energies as low as −1.52 eV under O-rich conditions, indicating their spontaneous formation and self-compensation, whereas the analogous Si-related complexes are significantly less favorable. Electronic structure and orbital analysis reveal that Sn generates localized 5s-derived in-gap states, whereas Si preserves delocalized 3p–O 2p bonding, consistent with the presence of in-gap states in Sn-doped but not Si-doped films. These findings identify dopant–vacancy coupling as the key mechanism governing compensation and provide a mechanistic basis for dopant selection and defect engineering in high-performance β-Ga2O3 devices.