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 (AlO x, GaO x, and HfO x ) 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 AlO x 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 cm 2 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.