Highly transparent undoped semiconducting ZnO thin films deposited at room temperature by rf-PERTE — Influence of rf power

Transparent, undoped semiconductive thin films of zinc oxide were deposited by radio frequency plasma enhanced reactive thermal evaporation of zinc rods in the presence of oxygen at room temperature, without any post-deposition annealing treatments. The study of the variation of rf power, in the range 5–200 W, on the main properties of these films was made. A decrease of the electrical conductivity of these films with increasing rf power was observed (10− 3 to 10− 12 (Ω cm)− 1), respectively, while the average visible transparency was kept practically constant (≈ 80%). From this initial study, a set of bottom-gate type thin-film transistors were made using the most promising semiconductor materials. Preliminary I(V) measurements showed all transistors working, with best results obtained from zinc oxide material deposited at the lowest rf power (20 W), within the deposition conditions range which leads to semiconductive material. Such devices presented an Ion (20 V)/Ioff (− 5 V) ratio of 6 × 106 and a field-effect mobility of 0.37 cm2/(V s).