Enhanced photogalvanic effect in the two-dimensional MgCl$_2$/ZnBr$_2$ vertical heterojunction by inhomogenous tensile stress

TL;DR

This paper demonstrates that applying inhomogeneous tensile stress to a MgCl₂/ZnBr₂ heterojunction significantly amplifies the photogalvanic effect, enhancing photocurrent by up to three orders of magnitude for UV photodetection.

Contribution

It introduces a novel method of using inhomogeneous mechanical strain to substantially boost the photogalvanic effect in 2D heterojunctions, improving their photodetection capabilities.

Findings

Photocurrent can be increased by up to 1000 times with strain.

Inhomogeneous tensile stress enhances device asymmetry.

Potential for low-power UV photodetectors.

Abstract

The photogalvanic effect (PGE) occurring in noncentrosymmetric materials enables the generation of a dc photocurrent at zero bias with a high polarization sensitivity, which makes it very attractive in photodetection. However, the magnitude of the PGE photocurrent is usually small, leading to a low photoresponsivity, and therefore hampers its practical application in photodetection. Here, we propose an approach to largely enhancing the PGE photocurrent by applying an inhomogenous mechanical stretch, based on quantum transport simulations. We model a two-dimensional photodetector consisting of the wide-bandgap MgCl$_2$/ZnBr$_2$ vertical van der Waals heterojunction with the noncentrosymmetric $C_{3v}$ symmetry. Polarization-sensitive PGE photocurrent is generated under the vertical illumination of linearly polarized light. By applying inhomogenous mechanical stretch on the lattice, the photocurrent can be largely increased by up to 3 orders of magnitude due to the significantly increased device asymmetry. Our results propose an effective way to enhance the PGE by inhomogenous mechanical strain, showing the potential of the MgCl$_2$/ZnBr$_2$ vertical heterojunction in the low-power UV photodetection.