Interplay between variable direct current sputtering deposition process parameters and properties of ZnO:Ga thin films

Abstract

Gallium-doped zinc oxide (GZO) is a potential transparent conductive oxide material suitable for modern photovoltaics among other applications. In this study, GZO thin films were deposited by a confocal direct current sputtering system to investigate the effects of various deposition parameters such as power (60 and 100 W), substrate temperature (50, 100, 150 and 200 °C) and sample location (3 spots) on optoelectronic properties of GZO films. In this regard, X-ray diffraction, ultraviolet-visible-infrared spectroscopy and Hall measurements were used primarily and the relevant analysis was presented in detail. It was found that the low power (60 W) deposition produces more superior optoelectronic properties than the high power (100 W) deposition yielding resistivity of 1.9 × 10−3 Ω·cm and over 89% average transmittance in the visible spectrum with the considerable improved blue response. The substrate temperature was found to improve optoelectronic properties and over 43% enhancement in the resistivity was achieved at the optimum temperature of 150 °C. In both aforesaid cases, improvement in the electrical conductivity was linked to the grain growth and the increase in free carriers. Effect of these two deposition parameters influenced the scale of optoelectronic uniformity, which was analyzed in three different spots. Finally, the adverse effect of spatial optoelectronic non-uniformity due to the high power deposition was observed. © 2018 Elsevier B.V.