Electrical properties of Pulsed Laser Deposited ZnO thin films

Epitaxial Single-crystal ZnO thin films have been grown on c-plane (0001) sapphire by Pulsed Laser Deposition process at different substrate temperatures (300 - 800 degrees C) with 10(-1) mbar oxygen pressure. The thicknesses of the films have been varied by varying number of pulses with a repetition rate of 10 pulse/sec. It is found that the sheet resistivity of ZnO thin films grown on c-plane sapphires are in the order of 10(-2) Omega-cm and it increases with increasing substrate temperatures and film thickness. The carrier concentrations and Hall mobility are found to be in the order of 10(17) cm(-3) and similar to 195 cm(2)/V-s, respectively. The Hall mobility slightly decreases with increase of substrate temperature and thickness of the films. It is also found that the ZnO films are structurally uniform and well oriented with perfect wurtzite structure with c/a ratio 5.1. We have also deposited non-epitaxial ZnO films on (100) p-Silicon substrates at the same conditions. From HR FE-SEM micrographs, surface morphology of ZnO films grown at lower substrate temperature are found to be uniform compared to the films grown at higher temperatures showing non-uniformity and misoriented wurtzite structures. However, the surface morphology of ZnO films grown epitaxially on (0001) sapphire are found to be more uniform and it does not change much with growth temperature. The resistivity of the films grown on p-Silicon at higher temperatures is in the order of 10(3) Omega-cm whereas films grown at lower substrate temperatures show comparatively lower resistivities (similar to 10(2) Omega-cm). From the recorded UV-Visible absorption spectrum the band gap of the film has been estimated to be 3.38 eV.