Opto-capacitive study of n-ZnO/p-Si heterojunctions elaborated by reactive sputtering method: Solar cell applications

Thin films of ZnO were deposited on glass and p-Si substrates by DC reactive sputtering, at different deposition times. The physical properties of the films were investigated by X-ray diffraction, UV-visible transmittance and four-probe measurements. The results show the improvement of the crystallinity, the transparency and the conductivity of films with increasing the thickness. The dark current-voltage, the capacitance-voltage and the spectral response characteristics of n-ZnO/p-Si heterojunctions revealed that the potential barrier profile and the interface state change strongly with the film thickness, which leads to an important difference in the carriers transport phenomena. The good rectifying behaviors were obtained for the thinner ZnO films (16-50 nm). Under illumination, the hetero-junctions with thinner films show a good photosensitivity in the visible range wavelength (~ 425 nm), while, the hetero-junctions with thick ZnO films exhibit a good photosensitivity in the visible and NIR regions (~ 1100 nm). The least thick ZnO film (16 nm) shows a photovoltaic behavior with a short circuit current density (Jsc) of ~ 1 mA/cm2 and an open voltage (Voc) of ~ 0.4 V.