Growth angle-dependent tunable work function and optoelectronic properties of MoOx thin films

In this work, the role of growth angle on the optoelectronic properties of sputter deposited MoOx thin films are investigated. X-ray diffraction studies reveal the amorphous nature of MoOx films. It is observed that the root mean square roughness of the films increases with increasing growth angle. In addition, the optical band gap shows a reduction with increasing deposition angle (from 0 degrees to 50 degrees) while an opposite trend is observed beyond that (up to 87 degrees). Compositional analyses shows that oxygen vacancy in MoOx films increases up to a growth angle of 50 degrees, whereas it decreases for films grown at even higher growth angles. Following this, Kelvin probe force microscopy is employed to determine the work function of MoOx films which shows the similar growth angle-dependent trend like band gap of the films. Further, current-voltage characteristics confirm the rectifying behaviour of all MoOx/Si heterojunctions, whereas the one corresponding to MoOx film grown under normally incident deposition flux shows the lowest leakage current. The observed tunability in different physical properties of MoOx films can be attributed to the growth dynamics, leading to growth angle-dependent variation in oxygen vacancy concentration in MoOx films. The present results are not only helpful from the fundamental point of view but also expected to grow MoOx films having tailor-made nanoscale functionality for fabrication of photovoltaic and photochromic devices. In particular, the films grown under normally incident flux will be highly suitable for constructing all oxide-based hole-blocking photovoltaic cells.