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.