Transport and electronic structure properties of MBE grown Sn doped Ga2O3 homo-epitaxial films

In this work, we report the transport, defect state and electronic structure properties of unintentionally doped (UID) and Sn doped β-Ga₂O₃ homo-epitaxial thin films grown by molecular beam epitaxy (MBE) with electron density ranging from 2.1 × 10¹⁶ to 2.8 × 10¹⁹ cm⁻³. The UID film with an electron density of 2.1 × 10¹⁶ cm⁻³ exhibits a notable RT mobility of 129 cm²/Vs and a peak mobility of 900 cm²/Vs at 80 K, achieving the state-of-the-art level for MBE-grown Ga₂O₃ films. Temperature dependent Hall measurement reveal that Sn dopants have an activation energy of 56.7 meV. Synchrotron-based photoemission spectroscopy were further used to study insights into the evolution of electronic properties induced by Sn doping. An in-gap defect state was observed at the 1.5 eV above the valence band maximum for the Sn-doped Ga₂O₃ film. The in-gap state acts as self-compensating centers affecting the overall doping efficiency and mobility. Furthermore, photoemission spectroscopic study also reveals an upward surface band bending existing at the surface region of Sn doped Ga₂O₃ films. The identification of the in-gap state and surface upward band bending have significant implications for understanding the doping mechanisms in Ga₂O₃ and its electronic device applications.