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

Abstract

We have investigated the structural and electrical properties of Ga-doped ZnO (GZO) thin films deposited by an RF magnetron sputtering at various RF powers from 50 to 90W. All the GZO thin films are grown as a hexagonal wurtzite phase with highly c-axis preferred parameters. The structural and electrical properties are strongly related to the RF power. The grain size increases as the RF power increases since the columnar growth of GZO thin film is enhanced at an elevated RF power. This result means that the crystallinity of GZO is improved as the RF power increases. The resistivity of GZO rapidly decreases as the RF power increases up to 70 W and saturates to 90W. In contrast, the electron concentration of GZO increases as the RF power increases up to 70 W and saturates to 90W. GZO thin film shows the lowest resistivity of <TEX>$2.2{\times}10^{-4}{\Omega}cm$</TEX> and the highest electron concentration of <TEX>$1.7{\times}10^{21}cm^{-3}$</TEX> at 90W. The mobility of GZO increases as the RF power increases since the grain boundary scattering decreases due to the reduced density of the grain boundary at a high RF power. The transmittance of GZO thin films in the visible range is above 90%. GZO is a feasible transparent electrode for application as a transparent electrode for thin film solar cells.