Photoelectric, stoichiometric and structural properties of n-ZnO film on p-Si

n-ZnO/p-Si heterojunction photodiodes have been fabricated by sputter deposition of n-ZnO films on p-Si substrates. Substrate temperatures of 300, 400, 500 and 600°C were used for the n-ZnO film deposition using various Ar/O₂ ratios from 1:1 to 6:1. All the diodes, except for one obtained at a high substrate temperature of 600°C, show strong rectifying behavior as characterized by current-voltage (I-V) measurement in a dark room. Photoelectric effects from the diodes have been observed under illumination using monochromatic red light with a wavelength of 670 nm. High levels of photocurrent or responsivity were obtained under reverse bias conditions when the stoichiometry of n-ZnO films was improved by optimizing the process conditions, such as the substrate temperature and Ar/O₂ ratio. The n-ZnO/p-Si structure prepared at 300°C was found to be unsuitable because photoelectric effects were not apparent from this structure. A heterojunction diode with n-ZnO deposited at 600°C was also found to be unsuitable because the dark leakage current was too high, even though the diode showed photoelectric effects.