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

TL;DR

This paper demonstrates that downscaling amorphous semiconductor devices can intrinsically enhance carrier mobility significantly, enabling high-speed thin film transistors for flexible electronics without material modifications.

Contribution

It introduces a band fluctuation framework showing mobility increase through device downscaling, a novel approach to improve amorphous semiconductor performance.

Findings

Carrier mobility of hydrogenated amorphous silicon increases by ~12 times at 10 nm gap.

Mobility enhancement does not affect device uniformity.

Downscaling reduces localized band tail states, improving mobility.

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.