Valence-State Controllable Fabrication of Cu2–xO/Si Type-II Heterojunction for High-Performance Photodetectors

Cuprite, nominally cuprous oxide (Cu2O) but more correctly Cu2–xO, is widely used in optoelectronic applications because of its natural p-type, nontoxicity, and abundant availability. However, the photoresponsivity of Cu2O/Si photodetectors (PDs) has been limited by the lack of high-quality Cu2–xO films. Herein, we report a facile room-temperature solution method to prepare high-quality Cu2–xO films with controllable x value which were used as hole selective transport layers in crystalline n-type silicon-based heterojunction PDs. The detection performance of Cu2–xO/Si PDs exhibits a remarkable improvement via reducing the x value, resulting in the optimized PDs with high responsivity of 417 mA W–1 and fast response speed of 1.3 μs. Furthermore, the performance of the heterojunction PDs can be further improved by designing the pyramidal silicon structure, with enhanced responsivity of 600 mA W–1 and response speed of 600 ns. The superior photodetecting performance of Cu2–xO/n-Si heterojunctions is attributed to (i) the matched energy level band alignment, (ii) the low trap states in high-quality Cu2O thin films, and (iii) the excellent light trapping. We expect that the low-cost, highly efficient solution process would be of great convenience for large-scale fabrication of the Cu2–xO thin films and broaden the applications of Cu2–xO-based optoelectronic devices.