Order in disorder: Increased carrier mobility of downscaled amorphous semiconductors as exemplified by hydrogenated amorphous silicon

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 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, 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 about 12 times, and this does not compromise device-to-device uniformity. This mobility improvement is a result of reduced localized band-tail states due to the ultrashort 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.