Investigation of optoelectronic performance in In, Ga co-doped ZnO thin films with various In and Ga levels

In, Ga co-doped ZnO (IGZO) thin films were deposited by radio frequency sputtering at room temperature in this study. The film's composition was adjusted by varying the sputtering power of ZnO, Ga2O3 and In targets. Compared with pure ZnO film, the crystallinity of IGZO films is obviously reduced, and the secondary phases such as In2O3 and ZnGa2O4 are detected. The influence of In, Ga, and Zn content on the optoelectronic properties of IGZO films is then investigated. Results show that the carrier mobility is sensitive to the decrement in Zn content, while the carrier concentration can be suppressed by increasing Ga content. In regards to the film's transmittance, In content plays a most important role. From the viewpoint of Haacke's figure of merit (FOM), IGZO films with high optoelectronic performance can be realized when In content is no more than 25 at.% and Ga content is limited to less than 10 at.%. In the end of this study, the electrical stability of IGZO film under different temperature and time conditions is analyzed. It reveals that IGZO film can withstand a temperature up to 450 °C; above this temperature, the film's conductivity significantly declines. Besides this, IGZO film is very stable in long-term operation under normal atmospheric conditions.