Effect of ITO buffer layers on the structural, optical and electrical properties of ZnO multilayer thin films prepared by pulsed laser deposition technique

ZnO/ITO/ZnO/ITO/ZnO five layer thin films are fabricated by pulsed laser deposition on quartz substrate kept at a substrate temperature (T-s) 873 K at a background oxygen pressure (pO(2)) of 0.05 mbar for different deposition duration for ZnO layers (5,10,15 and 20 min) while keeping a constant deposition time for ITO layers. The structural, optical and electrical properties of the as-deposited thin films have been investigated by GIXRD, AFIVI, UV-visible spectra, photoluminescence spectra and temperature-dependent electrical resistivity measurements (10-300 K) using four-probe technique. XRD patterns of the films show a polycrystalline nature. From the AFM images, the average grain size and mean surface roughness are estimated and the particles are densely packed in the film. A high transmittance is observed for all the films in the visible and IR region. The PL spectra show that the emission is in the UV and visible region due to the near band edge and deep level transitions of ZnO. The electrical resistivity of all the films are calculated and are very low compared to the reported values of as deposited ZnO thin films. The co-existence of very high transmittance in the visible region and very low dc resistivity enables these films suitable for optoelectronic device fabrications. The structural, optical and electrical studies reveal that ITO buffer layers improve the crystalline quality, optical and electrical properties of ZnO multilayered thin films. (C) 2009 Elsevier B.V. All rights reserved.