Tuning the Bandgaps of (Al_xGa_1−x)₂O₃ Alloyed Thin Films for High‐Performance Solar‐Blind Ultraviolet Fully Covered Photodetectors

Abstract Ga₂O₃ is a promising semiconductor for deep ultraviolet optoelectronics, because of its ultrawide bandgap of 4.85 eV. Here, the bandgap modulation of (Al_xGa_1−x)₂O₃ thin films through varying Al contents is reported –and the achievement of high‐performance photodetectors sensitive to the entire solar‐blind UV bands. It is shown that the bandgaps of (Al_xGa_1‐x)₂O₃ can be widely tuned from 4.85 eV to 5.9 eV. Solar‐blind ultraviolet photodetectors based on the (Al_xGa_1–x)₂O₃ films show detection cut‐off wavelengths varying from 263 to 236 nm, and response peaks varying from 238 to 209 nm. The photodetectors exhibit high performance with a high specific detectivity (up to 10¹⁵ Jones), low dark current (<0.35 nA), large photodark current ratio (≈10⁷), UV–vis rejection ratio (>10⁵), and long‐term device stability. Furthermore, a combination of high‐resolution X‐ray photoemission spectroscopy and density functional theory calculations is used to reveal insights into the evolution of electronic structures of (Al_xGa_1–x)₂O₃. The wide variations of the bandgap of (Al_xGa_1−x)₂O₃ mainly result from the upshift of the conduction band edges induced by the high energy Al 3s state hybridizing with the Ga 4s‐derived conduction band, while the valence band edge keeps almost the same for different Al content.