Enhancing the performance of ZnGa2O4 metal-semiconductor-metal ultraviolet solar-blind photodetectors by surface fluorine plasma sensitization

Abstract

ZnGa2O4 has a wide direct bandgap and excellent optical properties and is an emerging material for use in solar-blind ultraviolet (UV) photodetectors (PDs). Recently, metal-semiconductor-metal (MSM) based devices have gained popularity because of their low production cost, minimal design, flexible integration, and tunable performance. However, such devices suffer from low sensitivity. Herein, we propose a sensitization engineering strategy that involves surface fluorine plasma (SFP) treatment to enhance the performance of a ZnGa2O4 MSM solar-blind UV PD. Through this strategy oxygen vacancy defects are simultaneously passivated and the ratio of adsorbed oxygen species on the surface of the ZnGa2O4 thin film is changed. These modifications optimize the current under both dark and light conditions. In particular, the dark current has a trade-off relationship between the reduction in the oxygen vacancy concentration and changes in the crystal grain boundaries. As a result, the photocurrent is enhanced because of the increased amount of adsorbed oxygen. The PD prepared using a ZnGa2O4 thin film treated by SFP for 15 min exhibited excellent performance, specifically, it showed a large responsivity (42.22 A/W) and good specific detectivity (5.72 × 1014 Jones). Notably, these values are superior to those of most reported MSM solar-blind PDs. Moreover, the excellent rejection ratio and durability during repeated use demonstrate the benefits of SFP treatment for enhancing operating stability. Our study provides an effective avenue for optimizing the optoelectronic performance of oxide semiconductors.