Optical and electrical properties of ZnO films prepared by URT-IP method

Optical and electrical properties were studied on thin polycrystalline ZnO films (200-nm thick) deposited on glass substrates at 200 °C by a DC-arc ion plating method (URamoto-Tanaka-type ion plating method). Effects of the oxygen flow rate (OFR) on film properties were examined. The resistivity of undoped films changed from 4.2×10⁻³ to 9.6×10⁻¹ Ω cm, corresponding to the carrier concentration of 1.0×10²⁰-1.2×10¹⁸ cm⁻³, depending on the increase in OFR from 0 to 40 sccm. The Hall mobility tends to be the maximum value of 28 cm² (V s)⁻¹ at OFR of 10 sccm. Photoluminescence (PL) spectra exhibited a dominant near-band-edge (NBE) emission together with weak PL bands at 2.2 and 3.2 eV. Intensity of NBE was maximum at OFR of 10 sccm. Intensity of the PL band at 2.2 eV increased with increase in OFR. As a result of Ga-doping, the resistivity decreased and the carrier concentration increased by one order of magnitude. The optical transmittance was more than 90% in 400-1200 nm. The ZnO:Ga (3 and 4 wt.% Ga-doped) thin films with the lowest resistivity of 2.6×10⁻⁴ Ω cm, the highest mobility of 25 cm² (V s)⁻¹, and the highest PL intensity were obtained at OFR of 10 sccm. Further increase of OFR led to the decrease in both mobility and PL intensity.