Edge-induced Schottky barrier modulation at metal contacts to exfoliated molybdenum disulfide flakes

TL;DR

This paper investigates how narrowing MoS2 channels affects Schottky barrier heights at metal contacts, revealing edge effects that influence transistor performance and proposing edge passivation as a potential mitigation strategy.

Contribution

It provides the first detailed analysis of edge-induced Schottky barrier modulation in exfoliated MoS2, highlighting the importance of edge effects in device scaling.

Findings

Narrower MoS2 channels have higher Schottky barriers due to edge-induced band bending.

High dopant concentrations can reduce edge effects but are limited by mobility degradation.

Proper edge termination is necessary for further scaling of layered semiconductor transistors.

Abstract

Ultrathin two-dimensional semiconductors obtained from layered transition-metal dichalcogenides such as molybdenum disulfide (MoS2) are promising for ultimately scaled transistors beyond Si. Although the shortening of the semiconductor channel is widely studied, the narrowing of the channel, which should also be important for scaling down the transistor, has been examined to a lesser degree thus far. In this study, the impact of narrowing on mechanically exfoliated MoS2 flakes was investigated according to the channel-width-dependent Schottky barrier heights at Cr/Au contacts. Narrower channels were found to possess a higher Schottky barrier height, which is ascribed to the edge-induced band bending in MoS2. The higher barrier heights degrade the transistor performance as a higher electrode-contact resistance. Theoretical analyses based on Poisson's equation showed that the edge-induced effect can be alleviated by a high dopant impurity concentration, but this strategy should be limited to channel widths of roughly 0.7 micrometers because of the impurity-induced charge-carrier mobility degradation. Therefore, proper termination of the dangling bonds at the edges should be necessary for aggressive scaling with layered semiconductors.