Optical and Carrier Transport Properties of Cosputtered Zn–In–Sn–O Films and Their Applications to TFTs

The optical and carrier transport properties of amorphous transparent zinc indium tin oxide (ZITO) thin films and the characteristics of the thin-film transistors (TFTs) were examined as a function of chemical composition. The as-deposited films were very conductive and showed clear free carrier absorption (FCA). The analysis of the FCA gave the effective mass value of and a momentum relaxation time of 3.9 fs for an film with . TFTs with the as-deposited channels did not show current modulation due to the high carrier density in the channels. Thermal annealing at decreased the carrier density and TFTs fabricated with the annealed channels operated with positive threshold voltages when Zn contents were or larger. shifted to larger negative values, and subthreshold voltage swing increased with decreasing the Zn content, while large on–off current ratios were kept for all the Zn contents. The field effect mobilities ranged from 12.4 to for the TFTs with Zn contents varying from 5 to . The role of Zn content is also discussed in relation to the carrier transport properties and amorphous structures.