Tuning the Bandgaps of (AlxGa1−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 (AlxGa1−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 (AlxGa1-x)2O3 can be widely tuned from 4.85 eV to 5.9 eV. Solar-blind ultraviolet photodetectors based on the (AlxGa1–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 (AlxGa1–x)2O3. The wide variations of the bandgap of (AlxGa1−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.