Room-temperature synthesized amorphous P-type transparent Ga2O3-Cu2S alloy thin films with tunable optoelectronic properties

Ultra-wide bandgap Ga2O3 has many intriguing properties which make them potentially suitable for optoelectronic applications. However, its functionalities are largely hindered by the lack of p-type Ga2O3 based materials. In this work, we synthesized amorphous p-type transparent (Ga2O3)1-x(Cu2S)x alloy thin films with x<-0.5 by magnetron sputtering at room temperature. The optoelectronic properties of these alloy thin films were investigated by a combination of analytical techniques. The optical bandgap shows a reduction from-4.8 eV to-2.5 eV with increasing x, while the hole concentration N increases from 1019 cm-3 (x=-0.2) to-2 x 1021 cm-3 (x =-0.5), with their hole mobility mu -0.3 cm2 V-1 s- 1. The hole transport in these amorphous alloys follows the variable-range-hopping mechanism in the temperature range of 120-300 K. We observe that the valence band maximum (VBM) position moves up rapidly by-3 eV with x > 0.2 to-5.5 eV below the vacuum level, making the formation of native shallow acceptors more energetically favorable and hence enhancing their p-type conductivity. Our results show that electrical and optical properties of these amorphous p-type transparent (Ga2O3)1-x(Cu2S)x alloy thin films are potentially important in bipolar devices applications, e.g., Ga2O3 based p-n heterojunction power devices and high efficiency solar cells.