Crystal Phase, Electronic Structure, and Surface Band Bending of (InxGa1–x)2O3 Alloy Wide-Band-Gap Semiconductors

Abstract

Ga2O3 is emerging as a promising wide-band-gap semiconductor for high-power electronics and deep ultraviolet optoelectronics. Alloying Ga2O3 with In2O3 leads to the modulation of the band gaps and possible carrier confinement achieved at the heterointerface. In this work, we report a systematic study on the crystallographic phase, electronic structure, and surface band bending of (InxGa1–x)2O3 thin films over the whole composition range of 0 ≤ x ≤ 1 grown on α-Al2O3 (0001) substrates by pulsed laser deposition. It was found that with In content x < 0.2, a monoclinic β-phase of an (InxGa1–x)2O3 film is epitaxially grown on Al2O3 (0001), while a bixbyite phase of the (InxGa1–x)2O3 film grows when x ≥ 0.8. When 0.2 ≤ x < 0.8, a mixed β-phase and bixbyite phase coexist. The evolution of electronic structures of the (InxGa1–x)2O3 films was examined by high-resolution X-ray photoemission spectroscopy (XPS) and optical absorption spectroscopy. For the β-phase films, the optical band gaps decrease from 4.96 eV for Ga2O3 to 4.43 eV for x = 0.4, while for bixbyite (InxGa1–x)2O3, the optical band gaps slightly increase from 3.57 eV for In2O3 to 3.70 eV for x = 0.8. Detailed electronic structure study indicates that the decrease of band gaps of (InxGa1–x)2O3 with an increase of In content mainly results from the upper movement of the valence band edge because the shallow In 4d orbitals introduce a hybridized state with O 2p at the top of the valence band. In addition, the presence of surface electron accumulation (i.e., downward band bending) was identified at the surface region of the (InxGa1–x)2O3 films with x ≥ 0.6, which would provide an opportunity to modulate the surface electronic properties for device applications.