Sublimation-doping with super bases for high-performance solution-processed heterojunction oxide thin film transistors

Abstract

We elucidate how non-destructive sublimation-doping of In₂O₃/ZnO heterojunctions with various amidine-based organic dopants affects the degree of band bending of the heterojunction and thus the overall performance of solution-processed heterojunction oxide thin-film transistors (TFTs). Ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy analyses show that the stronger the basicity of the dopant, the smaller the E_C − E_F of ZnO that can be induced within a short doping time, resulting in a high electron mobility due to the increased electron density of the In₂O₃ layer at the vicinity of the heterointerface. Mott–Schottky analysis combined with secondary ion mass spectroscopy shows the preferential modification of E_C − E_F selectively for the ZnO layer. The use of a super base with the highest basicity exhibits a high electron mobility of 17.8 cm² V⁻¹ s⁻¹ for the SiO₂ and 37.8 cm² V⁻¹ s⁻¹ on average (46.6 cm² V⁻¹ s⁻¹ maximum) for the ZrO₂ dielectric layers and enhanced operational bias-stress stability via sublimation-doping for 6 min, which can be attributed to the trap-filled, percolation-limited charge transport behavior. Reproducibility tests are conducted for more than 50 independently fabricated TFTs using the optimized doping technique, and electron mobility distributions with deviations <±10% are demonstrated. This study shows that sublimation doping with super bases can be a good solution for high mobility oxide TFTs with stability and reliability.