Enhanced photo-response performance of Cu2O-based graded heterojunction optoelectronic devices with a Ga2O3 buffer layer

Abstract

Cuprous oxide (Cu₂O) has been widely investigated in optoelectronic devices because of its non-toxicity, high optical absorption coefficient, intrinsic p-type conductivity, and high hole mobility. However, misaligned energy levels remain an obstacle to obtaining efficient optoelectronic devices due to the extremely high conduction band minimum of Cu₂O. Here, a band-aligned wide bandgap Ga₂O₃ buffer layer is introduced and a graded heterojunction ZnO/Ga₂O₃/Cu₂O is realized. The oxygen-vacancy concentration and therefore the Fermi level, optical transmittance, and bandgap of the Ga₂O₃ films can be tuned by controlling the oxygen environment during pulsed laser deposition. The performance of the optoelectronic devices is improved by incorporating an optimized Ga₂O₃ buffer layer deposited at 1 Pa oxygen pressure with a deposition temperature of 100 °C. Photodetectors with a response range from the near-ultraviolet to the visible-light region, good linearity, fast response, and excellent long-term stability are demonstrated. In the meantime, an enhancement of the external quantum efficiency of 66% was reached by inserting the Ga₂O₃ buffer layer. Heterojunctions with gradient energy bands are confirmed to be effective in accelerating charge transport and suppressing carrier recombination through Kelvin probe force microscopy (KPFM) studies. Our work provides a new approach for developing self-powered ultraviolet and visible-light photodetectors with low-cost and high stability.