Structurally Unraveling the Photocarrier Behavior of Cu2O/ZnO Heterojunction Photodetectors

Photoelectric conversion in a semiconductor is the basis of photodetectors (PDs), so unraveling the photocarrier behavior is essential for designing and enhancing the performance of PDs. Herein, we experimentally uncover the generation and transport behavior of the photocarrier in the self-powered Cu2O/ZnO heterojunction PDs. The thickness of the functional layer is proved to be a major factor in determining the photocarrier generation and transport, namely, the increase in the number of photocarriers with the prolongation of the functional layer, while the transport of the carrier is impeded by the increase in the internal defects and becomes the degrading factor. By tuning the length of the ZnO nanorods, the structurally designed PD exhibits high responsivity of 45.74 mA/W under 450 nm light illumination at 0 V bias, which is 5.75 times larger than that of the quasi-planar one. Moreover, the PD presents a fast response speed (rise time of 5.5 ms and decay time of 5.9 ms) and long-term stability, showing only 3% degradation of the photocurrent after 30 days in the air. This work provides a microscopic perspective of photocarrier behavior for understanding the internal photoelectric conversion mechanism of the p–n junction-based PDs, which could further promote the practical applications of high-efficiency self-powered photodetectors.