Defects and doping mechanism in amorphous GaO x for solar-blind photodetectors applications

Abstract Solar-blind photodetectors (SBPDs) play a critical role in missile detection and secure communication. Compared to conventional crystalline materials, SBPDs based on amorphous GaO x (a-GaO x ) show satisfactory low cost and excellent stability. However, some basic issues have not been studied yet, such as why the SBPD based on Ga-rich a-GaO x has higher detectivity and why the nitrogen (N) annealing process could lower its dark current. The underlying defect and doping mechanism are not readily clarified by direct experimental observations, which hinders the further design of a-GaO x based SBPD. This work reveals the defect and doping mechanism in a-GaO x at the atomic scale by first-principles calculations. It is found that the stoichiometric and Ga-poor/O-rich a-GaO x tend to have a wide gap owing to the dative bonds formed by non-equivalent sp 3 -hybridized Ga orbitals and the lone-pair electrons of O. While for the Ga-rich a-GaO x , the Ga–Ga bonds formed by redundant Ga-atoms could introduce gap states and reduce the mid-gap, leading to a high response current and speed in Ga-rich GaO x based SBPDs. Besides, doping analyses reveal that the nitrogen atoms introduced by the annealing process in the Ga-rich sample should bond with oxygen atoms to reduce the band tail states, thereby decreasing the dark currents in Ga-rich GaO x . Finally, the presented atomic and electronic pictures further provide innovative theoretical insights for designing sensitive a-GaO x SBPDs with high detectivity.