Order in disorder: increased carrier mobility of downscaled amorphous semiconductors for high-speed thin film transistors in flexible electronics

Abstract

Amorphous semiconductors are important channel semiconductors in thin film transistors (TFTs) which serve not only active-matrix displays, but also flexible electronics for Internet of Things (IoT) applications. Nevertheless, a great limitation of amorphous semiconductors is their low carrier mobilities relative to their monocrystalline counterparts. Based on a recently established band fluctuation framework [Y. Luo and A. Flewitt, Phys. Rev. B 109, 104203 (2024)], this paper shows that the intrinsic carrier mobility of amorphous semiconductors can significantly increase simply through device downscaling, without any material-level optimizations. Specifically, it is revealed that the intrinsic electron mobility of hydrogenated amorphous silicon in a 10-nm long gap can increase by around 12 times, and does not compromise device-to-device uniformity. This mobility improvement is a result of reduced localized band tail states due to the ultra-short gap length relative to the band fluctuation length scale before downscaling; the latter is determined by the short- and medium-range structural order of the amorphous semiconductor.