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 × 10²¹ cm⁻³ (x = ∼0.5), with their hole mobility μ ∼ 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.