(Invited) Amorphous Zinc Oxysulfide Thin Films: Synthesis, Physical Properties, and TFT Application

Abstract

Amorphous oxide semiconductors (AOSs) have been under extensive research during recent years. Because of their high electron mobility even under amorphous state, they have been widely used as key materials for flat panel displays and flexible electronics devices, especially as channel layer of thin film transistor (TFT). Recently, it has been reported that an amorphous mixed-anion semiconductor consisting of only earth-abundant elements, zinc oxynitride (a-ZnON), shows high electron mobility and capability to TFT application [1]. However, a-ZnON is unstable in air due to weak chemical bonds between Zn and N [2]. To overcome this drawback, we synthesized another earth-abundant amorphous mixed-anion semiconductor, amorphous zinc oxysulfide (a-ZnOS) thin films and found that their electron mobility is comparable to those of conventional AOSs (~15 cm2V-1s-1), in addition to good chemical stability under ambient conditions [3]. Successively, a-ZnOS based TFTs were fabricated with bottom-gate and top contact configuration. a-ZnOS thin films with S/(S+O) = ~0.30 shows obvious TFT performance in the pristine states, although their field effect mobility (μ FE) was moderate (μ FE <1 cm2V−1s−1). μ FE increased with the decrease of S/(S+O), but the carrier density became too large for TFT operation. By annealing these films in vacuum at 150 °C for 10 min, their TFT performance was significantly improved; on/off ration over 104 and μ FE over 10 cm2V−1s−1.[1] Kim et al., Sci. Rep. 3, 1459 (2013).[2] Lee et al. Appl. Phys. Lett. 107, 122105 (2015)[3] Y.Zhu et al., Adv. Electron. Mater. 6, 1900602 (2019).