Effect of Ar/O2 gas ratios on the structure, electrical and optical properties of Na-doped ZnCdO film synthesized by magnetron sputtering

Abstract

Na-doped ZnCdO films [ZCO:Na] were grown on quartz substrates at different ratios of argon to oxygen gas flow (Ar:O2) by the radio frequency magnetron sputtering method. The influence of Ar:O2 ratio on structure, electrical and optical properties was investigated by using X-ray diffraction, X-ray photoelectron spectroscopy, Transmission electron microscopy, Hall measurements (Hall), optical absorption spectra and Photoluminescence. Results indicated that all obtained ZCO:Na thin films possess the hexagonal wurtzite structure and free from the formation of secondary phases. As the Ar:O2 ratios change from 1:5 to 5:1, at first the Eg increases with the Ar:O2 ratios increasing and reaches a maximum value at the Ar:O2 ratio of 1:1, then decreases evidently with the Ar:O2 ratios increasing continually. It is found that the lower Ar:O2 ratio is propitious to obtain n-type ZCO:Na film, while the relative higher Ar:O2 ratio is required to obtain p-type ZCO:Na thin films. When the Ar:O2 ratio is 1:1, the ZCO:Na film shows the best p-type conduction characteristics, which has a hole concentration of 1.13 × 1016 cm−3, Hall mobility of 2.54 cm2 V−1 s−1 and resistivity of 2.53 × 102 Ω cm. In addition, the mechanism of the influence of Ar:O2 ratio on the electrical and optical properties of the film as well as the mechanism of p-type conductivity was discussed in this work.