Engineering High-k Oxide/CuSCN Interface for p-Channel Thin-Film Transistors

Copper(I) thiocyanate (CuSCN) is a unique coordination polymer semiconductor with excellent hole-transport properties and a wide band gap. CuSCN enables the construction of thin-film transistors (TFTs) based on a transparent p-type inorganic channel layer─a rare component. Despite the tremendous progress of TFTs based on transparent n-type oxides, the development of the p-type counterparts has been limited, especially for TFTs based on CuSCN. In this work, we explored three aspects in bottom-gate top-contact TFTs: the use of high-k metal oxides (AlOx, GaOx, and HfOx) as the dielectric layer, organic molecules (methacrylic acid or MAA and tetraethyl orthosilicate or TEOS) as the dielectric passivation layer, and an antisolvent (tetrahydrofuran or THF) to improve the hole-transport properties. The best condition was found to be AlOx annealed at 200 °C with the TEOS layer as the dielectric combined with THF-treated CuSCN as the semiconducting channel. The resulting TFTs operated under low voltages and showed a field-effect hole mobility in the range of 7–8 × 10–3 cm2 V–1 s–1, representing an increase of 4- to 5-fold from the previous report. In particular, the TEOS passivation layer and THF treatment increased the mobility as a result of the reduced trap state density.