Amorphous Mixture of Two Indium-Free BaSnO and ZnSnO for Thin-Film Transistors with Balanced Performance and Stability.

The trade-off between performance and stability in amorphous oxide semiconductor-based thin-film transistors (TFTs) has been a critical challenge, meaning that it is difficult to simultaneously achieve high mobility and stability under bias and light stresses. Here, an amorphous mixture of two indium-free BaSnO and ZnSnO compounds, a-(Zn,Ba)SnO, is proposed as a feasible strategy to achieve high mobility and stability at the same time. The choice of BaSnO as a counterpart to ZnSnO, a well-known In-free candidate in amorphous oxide semiconductors, is to improve structural order and oxygen stoichiometry due to the large heat of formation and to preserve electron mobility due to the same kind of octahedral Sn-O network. Our first-principles calculations indeed show that compared to pure a-ZnSnO, BaSnO plays a crucial role in restoring structural order in both stoichiometric and O-deficient supercells without seriously damaging the conduction band minimum. The resulting features of a-(Zn,Ba)SnO reduce O-deficiency and the valence band tail states, which are known to be critically associated with instability. It is experimentally demonstrated that a-(Zn,Ba)SnO-based TFTs simultaneously exhibit high mobility (>20 cm V s) and remarkable stability against negative bias illumination stress (Δ: <0.9 V). Our results suggest that a-(Zn,Ba)SnO would be a strong In-free candidate for next-generation TFT display, replacing the conventional a-InGaZnO.