Valence-State Controllable Fabrication of CuO/Si Type-II Heterojunction for High-Performance Photodetectors.

Cuprite, nominally cuprous oxide (CuO) but more correctly CuO, is widely used in optoelectronic applications because of its natural p-type, nontoxicity, and abundant availability. However, the photoresponsivity of CuO/Si photodetectors (PDs) has been limited by the lack of high-quality CuO films. Herein, we report a facile room-temperature solution method to prepare high-quality CuO films with controllable value which were used as hole selective transport layers in crystalline n-type silicon-based heterojunction PDs. The detection performance of CuO/Si PDs exhibits a remarkable improvement via reducing the value, resulting in the optimized PDs with high responsivity of 417 mA W 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 and response speed of 600 ns. The superior photodetecting performance of CuO/n-Si heterojunctions is attributed to (i) the matched energy level band alignment, (ii) the low trap states in high-quality CuO 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 CuO thin films and broaden the applications of CuO-based optoelectronic devices.