High  Current On/Off Ratio and Detectivity Α-Ga2o3-Tio2 Core-Shell Nanorods Based Self-Powered Deep Ultraviolet Photodetector Through Defect Passivation

Abstract

Recently, α -Ga 2 O 3 nanorod arrays (NRAs) based deep ultraviolet (DUV) photodetectors attract more and more attention in the optoelectronic field due to their wide bandgap, highly effective detection area, and simple preparation method. Unfortunately, the large number of defects in the α -Ga 2 O 3  NRAs hinder the transportation of charge carriers, resulting in low on-off ratio, low responsivity, and low detectivity. Wide bandgap materials such as TiO 2  and Al 2 O 3  are often used as surface passivation layers to passive the defects in the semiconductor, which is an effective way to improve the performance of photodetectors. Herein, a α -Ga 2 O 3 -TiO 2  core-shell NRAs based photovoltaic type DUV photodetector with the optimized graphene upper electrode has been successfully fabricated. Thanks to the passivation effect and type-II staggered band alignment of α -Ga 2 O 3  and TiO 2 , the photo-generated carriers can be separate and transport efficiently. The α -Ga 2 O 3 -TiO 2  core-shell NRAs photodetector exhibits a large photocurrent of ~110.5 nA, a responsivity ( R ) of 0.176 mA/W, a response speed of 0.72/0.14 s, and an I dark /I photo  current ratio of 616 under a 254 nm light at 0 V. In addition, the effect of humidity on the α -Ga 2 O 3 -TiO 2 NRAs device has been studied, and a proposed model of the mechanism has been built. Our work provides a feasible strategy to high-performance α -Ga 2 O 3 NRAs based photodetector, which may push forward their applications.

Keywords: Ga2O3, Deep ultraviolet photodetector, Vertical nanorod arrays, Core-shell structure, Defect passivation