Annealing effects on titania doped zinc oxide (ZNO:TI) and gallium doped zinc oxide (ZnO:GA) thin films prepared by DC-magnetron sputtering
Transparent conductive oxides (TCO) are used as transparent electrodes in thin film solar cells. Especially for CdTe solar cells, the successive production processes require high temperature stability for the TCO material. ZnO:Ti and ZnO:Ga thin layers can resist temperatures up to 600°C while having a smooth surface and good electrical and optical properties. Layers of zinc oxide doped with titania or gallium oxide were deposited on glass substrates using magnetron sputtering from a single planar cathode (length of 750mm). The thin film properties were investigated and compared to aluminum doped zinc oxide (ZnO:Al). The sputtering power was set to the upper load limit of the targets to deposit thick layers with a deposition rate of more than 100 nm·m/min. Additionally, the thin films were annealed at high temperatures of up to 600°C in vacuum or ambient air. Depending on the sputtering parameters and the annealing treatment the resulting resistivity was less than 300 ?Wcm for ZnO:Ga and less than 1000 ?Wcm for ZnO:Ti with a high transmission in the visible spectral range. In contrast to ZnO:Al layers, the electrical properties of ZnO:Ga and ZnO:Ti thin films do not deteriorate at high annealing temperatures. The thin films were analyzed by UV-VIS spectroscopy as well as Hall measurements. SEM and XRD measurements were carried out to examine the thin film surface and structure.