Improved Photoelectric Performance with Self-Powered Characteristics through TiO₂ Surface Passivation in an α-Ga₂O₃ Nanorod Array Deep Ultraviolet Photodetector

Recently, α-Ga2O3 nanorod array (NRA)-based deep ultraviolet (DUV) photodetectors have attracted more and more attention in the optoelectronic field due to their wide band gap, highly effective detection area, and simple preparation method. Unfortunately, the large number of defects in the α-Ga2O3 NRAs hinder the transportation of charge carriers, resulting in a low on–off ratio, low responsivity, and low detectivity. Wide band gap materials such as TiO2 and Al2O3 are often used as surface passivation layers to passive the defects in semiconductors, which is an effective way to improve the performance of photodetectors. Herein, an α-Ga2O3–TiO2 core–shell NRA-based photovoltaic-type DUV photodetector with an optimized graphene upper electrode has been successfully fabricated. Thanks to the passivation effect and type-II staggered band alignment of α-Ga2O3 and TiO2, the photogenerated carriers can be separated and transported efficiently. The α-Ga2O3–TiO2 core–shell NRA photodetector exhibits a large photocurrent of ∼110.88 nA, a responsivity (R) of 0.176 mA/W, a photoresponse speed of 0.72/0.14 s, and an Idark/Iphoto current ratio of 616 under 254 nm light at 0 V. In addition, the effect of humidity on the α-Ga2O3–TiO2 NRA device has been studied, and a proposed model of the mechanism has been built. Our research suggests a possible technique for developing high-performance α-Ga2O3 NRA-based photodetectors, which has the potential to further their applications.