Cu-Doped Ga2O3 Thin Films Enabling High-Performance p-Type Solar-Blind Photodetectors

Abstract

Low hole mobility, strong hole trapping, and self-compensation effects limit the achievement of stable p-type conductivity in the β-Ga2O3 semiconductor, thereby inhibiting its application in advanced electronic devices. From a theoretical standpoint, the relatively flat nature of the valence band maximum (VBM) with dominant oxygen vacancy-related donor states constitutes a major bottleneck that intrinsically drives the material toward n-type conductivity. In this study, we successfully achieved p-type conductivity in gallium oxide thin films using copper doping. The introduction of controlled Cu as an acceptor dopant using RF magnetron sputtering into the Ga2O3 film facilitates bipolar transport by creating an acceptor impurity level near the valence band maximum (VBM), resulting in conductivity modulation. X-ray photoelectron spectroscopy (XPS) and capacitance–voltage (C–V) measurements provide evidence of p-type conduction with a high hole concentration on the order of 1019cm–3. The positive Seebeck coefficient (S) further confirms hole-dominated electrical transport. Moreover, theoretical analysis reveals that the Cu-induced localized states near the VBM predominantly originate from Cu-d states hybridized with O-p states, indicating strong local Cu–O interactions at the octahedral sites and providing microscopic insight into the experimentally observed modulation of electrical conductivity. Finally, a solar-blind photodetector was fabricated using optimized copper-doped p-type gallium oxide thin films. The fabricated device demonstrates remarkably high performance with a photo-to-dark current ratio (PDCR) of 157.33 ± 0.88, responsivity of 806.88 ± 20.55 A/W, external quantum efficiency of (4.01 ± 0.10) × 105%, noise-equivalent power of (1.88 ± 0.01) × 10–13 W Hz–1/2, and a specific detectivity of (2.58 ± 0.05) × 1012 Jones at 250 nm with a moderate bias of 5 V at a 1 Hz frequency, demonstrating consistent performance across five nominally identical devices. These findings show that the interfacial electrostatics and charge-transport mechanisms in Ga2O3 Schottky devices are efficiently tuned by regulated Cu inclusion, offering insights for enhancing ultra-wide-bandgap oxide-related devices.