Effect of vacuum annealing on the photoconductivity of CuO thin films grown using sequential ionic layer adsorption reaction

Using sequential ionic layer adsorption reaction technique, Cupric Oxide (CuO) thin films were deposited on a glass substrate at relatively low bath temperature of 338 +/- 5 K. The as deposited films were polycrystalline in nature with preferential orientation along the (200) plane. The films were found to exhibit negative photoconductivity. Vacuum annealing of the films resulted in preferential growth along the (111) and (200) plane for temperatures 373 K, 473 K and 573 K. Vacuum annealing at 673 K resulted in preferential growth along the (200) plane. The vacuum annealed films showed normal photoconductivity behavior. The optical band gap of the films was found to increase from 1.57 eV for the as prepared films to 2.06 eV for films annealed in vacuum at 673 K. Surface photo voltage measurements indicate that the direction of band bending is reversed when the as deposited CuO thin films are subjected to vacuum annealing. We conclude that surface state passivation is leading to change in the photoconductive behavior of the thin film samples when subjected to post deposition vacuum annealing. (C) 2016 Elsevier B.V. All rights reserved.