Optical and Electrical Properties of a Metal-Semiconductor-Metal Material Based on Al-Doped ZnO Films for Use as UV Photodetectors

Abstract

ZnO and ZnO:Al (aluminum-doped ZnO) thin films were grown on glass substrates at 480 °C by using a simple flexible spray pyrolysis method. The effects of Al doping on the structural, optical and electrical properties were investigated. X-ray diffraction (XRD) patterns showed successful growth of high-quality polycrystalline films on the substrates. The predominant orientation of the films was the (002) orientation. The microstructural parameters, such as the lattice parameters, the crystallite size (D), the microstrain (∈), and the dislocation density (d) were calculated and found to depend upon the composition. Adding Al to the ZnO crystal structure decreased the crystallite size and increased the residual stress in the thin films. All films were highly transparent in the visible region with an average transmittance of 85 %. Increasing the amount of the Al dopant increased the optical band gap from 3.26 to 3.34eV. A blue shift of the optical band gap from 400 nm to 380 nm with increasing Al doping percentage was observed in the PL spectrum. The spectrum in the UV range showed 1% Al emission with a bandwidth of 100 nm (between 350 and 450 nm). Doping improved the electrical conductivity of the ZnO thin films, and the lowest resistivity was found for the thin film with 1% Al doping. The I-V characteristics of the ZnO:Al thin films were measured in dark and under UV illumination. This study demonstrated that the 1% Al-doped ZnO thin film exhibited physical properties, allowing better integration in optoelectronic devices