On the temperature and humidity effects of contact electrification in semiconductor-semiconductor case: An energy band model for electron transfer in triboelectrification

Contact electrification (CE) (or triboelectrication) is a well-known phenomenon, but the identity of the charge carriers and their charge transfer mechanism have been under controversy. In recent years, some progress has been made in the study of CE mechanism in metal/dielectric-dielectric cases (in which cases the charge transfer is mainly dominated by the electron transfer mechanism), but the mechanism of CE in semiconductor-semiconductor (S-S) cases is still not well known. In this study, we chose ZnO-Si as friction pairs and conducted a series of studies on the effects of the conductivity type and doping concentration of Si wafer and further investigated the ambient temperature and humidity effects on CE in S-S cases. The results show that the CE in S-S cases is a charge transfer process dominated by the electron transfer mechanism. We describe the electron transfer in the contact-separation (CS) process with an energy band model, and explain the following principle more intuitively: the larger the Fermi energy level difference between the semiconductor friction layers is, the larger the number of transferred electrons are in CS process and the higher the output of CS-TENG is; the main influence mechanism of temperature on CE in S-S cases is thermal electron emission; and the influence of humidity on CE in S-S cases is mainly caused by the change of the surface state density of the friction layers by the adsorption of water molecules. This work not only clarifies that the charge transfer in S-S CE is dominated by the electron transfer mechanism originated from the Fermi energy level difference, but also proposes a more complete energy band model to explain the semiconductor-semiconductor CE mechanism, including the mechanism of the effect of temperature and humidity on the output performance of S-S CS-TENG, which is of great significance to improve the application potential of S-S TENG.