Buffer-assisted low temperature growth of high crystalline quality ZnO films using Pulsed Laser Deposition

Pulsed Laser Deposition of high crystalline quality thin ZnO films on sapphire substrates necessitates a growth temperature of about 750 °C or higher while sharp interfaces in a multilayer structure suitable for optoelectronic devices are obtained at comparatively low growth temperatures. To meet these contradictory requirements a growth scheme has been evolved in which a ZnO buffer layer deposited at about 750 °C was found to facilitate high crystalline quality growth of a ZnO over layer even at 400 °C. The buffer layer grown at 750 °C was found to have its in plane lattice 30° rotated compared to that of the sapphire substrate and so was the case with the ZnO over layer grown at 400 °C on the buffer. The full width at half maximum of the high resolution X-ray diffraction rocking curves of (00.2) and (10.4) peaks of ZnO films grown at low temperature on the buffer were found to be ∼0.18° and ∼0.28°, respectively, which are comparable to 0.11° and 0.23° as observed in the case of films deposited directly at 750 °C and much better than the values of 0.46° and 0.48° seen in case of the films grown at 400 °C without any buffer layer. The buffer assisted low temperature ZnO growth also decreased the r.m.s. value of the surface roughness of the film to about 8 Å from about 40 Å of the one grown at high temperature without any buffer.