Modulation Mechanism of ZnO/P-Si Contact Electrification by Ultraviolet-Excited Photocarriers in Contact-Electro-Junction

Self-powered ultraviolet (UV) photodetector devices are considered as one of the development trends of UV photodetector devices. The triboelectric nanogenerator (TENG) has great application prospects in the field of self-powered UV photodetection. However, the modulation mechanism of contact electrification (CE) by UV light is unclear at present, which makes the application of the TENG on UV photoelectric detectors difficult. In this study, the modulation mechanism of ZnO/P-Si CE by UV light was investigated via varying the wavelength and intensity of UV illumination, and the mechanism of the photorelaxation phenomenon of ZnO/P-Si CE after UV illumination was further investigated by controlling the on/off of the UV light during the separation of the friction pairs. The results show that UV light can control the output performance of ZnO/P-Si CE: the decrease of CE under 254 nm UV light is larger than that under 365 nm UV light; furthermore, the reduction in performance intensifies with increasing light intensity. We propose the concept of the contact-electro-junction (CEJ) and describe the carrier migration process in the space charge region at CE between semiconductors with the energy band diagram model. UV light leads to quasi-Fermi energy level splitting in ZnO, which reduces the net carrier transfer in the CEJ, and thus, the output performance of CE decreases. In addition, the photorelaxation phenomenon occurs in CE after illumination, and this phenomenon is related to the recombination rate of photocarriers, demonstrating the intermodulation of UV light and CE. This work not only helps to further understand the CE in semiconductor-semiconductor case but also utilizes the energy band diagram model to explain the modulation mechanism of ZnO/P-Si CE by photocarriers in CEJ, which is of great significance to improve the potential of TENG for UV photodetection applications.