Effect of Deposition Temperature on Structural and Electrical Properties of Ga-Doped ZnO for Transparent Electrode of Thin Film Solar Cells

Abstract

We have investigated the structural and optical properties of Ga-doped ZnO (GZO) thin films deposited by RF magnetron sputtering at various deposition temperatures from 100 to <TEX>$500^{\circ}C$</TEX>. All the GZO thin films are grown as a hexagonal wurtzite phase with highly c-axis preferred parameter. The structural and electrical properties are strongly related to deposition temperature. The grain size increases with the increasing deposition temperature up to <TEX>$400^{\circ}C$</TEX> and then decreases at <TEX>$500^{\circ}C$</TEX>. The dependence of grain size on the deposition temperature results from the variation of thermal activation energy. The resistivity of GZO thin film decreases with the increasing deposition temperature up to <TEX>$300^{\circ}C$</TEX> and then decreases up to <TEX>$500^{\circ}C$</TEX>. GZO thin film shows the lowest resistivity of <TEX>$4.3{\times}10^{-4}\;{\Omega}cm$</TEX> and highest electron concentration of <TEX>$1.0{\times}10^{21}\;cm^{-3}$</TEX> at <TEX>$300^{\circ}C$</TEX>. The mobility of GZO thin films increases with the increasing deposition temperature up to <TEX>$400^{\circ}C$</TEX> and then decreases at <TEX>$500^{\circ}C$</TEX>. GZO thin film shows the highest resistivity of 14.1 <TEX>$cm^2/Vs$</TEX>. The transmittance of GZO thin films in the visible range is above 87% at all the deposition temperatures. GZO is a feasible transparent electrode for the application to the transparent electrode of thin film solar cells.