Effect of oxygen ambient on structural, optical and electrical properties of epitaxial Al-doped ZnO thin films on r-plane sapphire by pulsed laser deposition

Al-doped ZnO (ZnO:Al) thin films were grown epitaxially on r-plane sapphire substrate by pulsed laser deposition. Substrate temperature of 400 °C and pulsed repetition rate of 5 Hz was kept constant during the deposition. The effect of oxygen ambient pressure from 0.1 to 10 mTorr on structural, optical and electrical properties of the ZnO:Al films were investigated. The lowest resistivity was found to be 2.14 × 10−3 Ω-cm with a carrier concentration of 6.89 × 1019 cm−3 for the film deposited in 1 mTorr of oxygen pressure. ZnO:Al film revealed smoother surface obtained at oxygen ambient pressure of 1 mTorr. The epitaxial relationship between ZnO:Al films and r  -plane sapphire was found to be (0001)ZnO//(011¯2)sappand[101¯0]ZnO//[01¯11]sapp. Photoluminescence spectra of the film grown at the oxygen ambient pressure of 1 mTorr exhibited peak at 3.34 eV, without any deep level.