Identification and modulation of electronic band structures of single-phase β-(AlxGa1-x)2O3 alloys grown by laser molecular beam epitaxy

Understanding the band structure evolution of (AlxGa1-x)(2)O-3 alloys is of fundamental importance for developing Ga2O3-based power electronic devices and vacuum ultraviolet super-radiation hard detectors. Here, we report on the bandgap engineering of beta-(AlxGa1-x)(2)O-3 thin films and the identification of compositionally dependent electronic band structures by a combination of absorption spectra analyses and density functional theory calculations. Single-monoclinic beta-phase (AlxGa1-x)(2)O-3 (0 <= x <= 0.54) films with a preferred (-201) orientation were grown by laser molecular beam epitaxy with tunable bandgap ranging from 4.5 to 5.5 eV. The excellent fitting of absorption spectra by the relation of (alpha hv) proportional to (hv-E) unambiguously identifies that beta-(AlxGa1-x)(2)O(3 )alloys are indirect bandgap semiconductors. Theoretical calculations predict that the indirect nature of beta-(AlxGa1-x)(2)O-3 becomes more pronounced with increased Al composition due to the increased eigenvalue energy gap between M and Gamma points in the valence band. The experimentally determined indirect bandgap exhibits almost a linear relationship with Al composition, which is consistent with the theoretical calculation and indicates a small bowing effect and a good miscibility. The identification and modulation of (AlxGa1-x)(2)O-3 band structures allows rational design of ultra-wide bandgap oxide heterostructures for the applications in power electronics and solar-blind or X-ray detection. Published by AIP Publishing.