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.