Stark Effect of Doped Two-Dimensional Transition Metal Dichalcogenides

TL;DR

This study reveals how doping uniquely influences the Stark effect in 2D transition metal dichalcogenides, with electron doping causing nonlinear and hole doping causing linear Stark effects, impacting device tuning.

Contribution

It uncovers the distinct doping-dependent Stark effects in 2D TMDs, highlighting the importance of doping in device applications and revealing a new tuning mechanism for band gaps.

Findings

Doped electrons screen external fields leading to nonlinear Stark effects.

Doped holes do not effectively screen, resulting in linear Stark effects.

The doping effect observed is general across 2D layered materials.

Abstract

The band gap of two-dimensional (2D) semiconductors can be efficiently tuned by gate electric field, which is so called the Stark effect. We report that doping, which is essential in realistic devices, will substantially change the Stark effect of few-layer transition metal dichalcogenides in unexpected ways. Particularly in bilayer structures, because of the competition between strong quantum confinement and intrinsic screening length, electron and hole dopings exhibit surprisingly different Stark effects: doped electrons actively screen the external field and result in a nonlinear Stark effect; however, doped holes do not effectively screen the external field, causing a linear Stark effect that is the same as that of undoped materials. Our further analysis shows that this unusual doping effect is not limited within transition metal dichalcogenides but general for 2D structures. Therefore, doping plays a much more crucial role in functional 2D devices and this unusual Stark effect also provides a new degree of freedom to tune band gaps and optical properties of 2D materials.