Optical and electrical properties of URT-IP ZnO thin films for photovoltaic devices

Abstract

Optical and electrical properties have been studied on thin polycrystalline ZnO films deposited on a glass substrate by Uramoto–Tanaka type ion plating (DC-arc ion-plating) method with relation to the oxygen flow rate (OFR) in the deposition chamber and to the Ga-doping concentration. For undoped films, an increase of OFR led to increase in the resistivity and decrease in the carrier concentration. At OFR of 10 sccm, both the Hall mobility and the near-band-edge photoluminescence (PL) intensity were the maximum, and the good-quality film was obtained at this OFR. Further increase of OFR led to the decrease in the Hall mobility and the increase in the intensities of defect-related PL bands. The Ga-doping reduces the resistivity by one order of magnitude. The Hall mobility and PL intensity were the maximum at OFR of 10 sccm, and the crystal quality is good at this OFR. ZnO:Ga films exhibited very broad near-band-edge PL, and the effect of the Ga-doping on PL is discussed. The optical transmittance was more than 90% invisible. The decrease in the optical transmittance and increase in the reflectance were observed for wavelength longer than 1200 nm for films with high carrier concentration of approximately 10 21 cm −3.