Microstructure Evolution and Electrical Behaviors for High-Performance Cu₂O/Zr-Doped β-Ga₂O₃ Heterojunction Diodes

Beta-gallium oxide (β-Ga₂O₃) is emerging as a promising ultrawide band gap (UWBG) semiconductor, which is vital for high-power, high-frequency electronics and deep-UV optoelectronics. It is especially significant for flexible wearable electronics, enabling the fabrication of high-performance Ga₂O₃-based devices at low temperatures. However, the limited crystallinity and pronounced structural defects arising from the low-temperature deposition of Ga₂O₃ films significantly restrict the heterojunction interface quality and the relevant electrical performance of Ga₂O₃-based devices. In this work, cuprous oxide (Cu₂O)/Zr-doped β-Ga₂O₃ heterojunction diodes are fabricated by magnetron sputtering without intentional substrate heating, followed by an investigation into their microstructure and electrical behaviors. Zr doping can markedly enhance the Ga₂O₃ crystallinity at low substrate temperatures, transforming the amorphous structure of pristine Ga₂O₃ films into the crystallized β phase. Moreover, crystalline β-Ga₂O₃ facilitates the epitaxial growth of the Cu₂O phase, suppressing the formation of detrimental secondary phase CuO at the heterojunction interface. Benefiting from the high-quality heterojunction interface, the Cu₂O/Zr-doped β-Ga₂O₃ heterojunction diode exhibits a near-ideal electrical behavior with a low ideality factor of 1.6. The consistent electrical parameters extracted from current-voltage (J-V) and capacitance-voltage (C-V) measurements also confirm the high quality of β-Ga₂O₃. This work highlights the potential for the low-temperature production of high-quality β-Ga₂O₃-based heterojunction devices through Zr doping.