Effects of vacuum annealing on carrier transport properties of band gap-tunable semiconducting amorphous Cd–Ga–O thin films

Abstract

The effect of vacuum annealing on the amorphous oxide semiconductor Cd–Ga–O system with a tunable band gap was examined. While the amorphous halo peak in XRD patterns of the films with Cd concentration of ~70% started sharpening after annealing at a temperature ≥200°C. In contrast, the films with Cd content of ~50% and ~20% were not crystallized for annealing temperatures up to 700°C. Carrier concentrations and Hall mobilities of ~70% and ~50% films were maximized by annealing at 400°C and 500°C, respectively, regardless of the properties of the as-deposited films, which were varied because of the unintended variation of deposition conditions such as the residual water vapor pressure in the deposition chamber. The initial electrical conductivity of ~20% films widely varied from <10−8 to 11S·cm−1, and annealing at 500°C was required for obtaining conductive films from the insulating as-deposited films. The maximum Hall mobility for films with Cd content of ~70% and ~50% films was ≥10cm2V−1s−1 and that for the film with ~20% Cd content was ≥3cm2V−1s−1.