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

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 11 S·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 ≥ 10 cm2 V− 1 s− 1 and that for the film with ~ 20% Cd content was ≥ 3 cm2 V− 1 s− 1.