Piezoelectric networks and ferroelectric moir\'e superlattice domains in twistronic WS$_2$/MoS$_2$ and WSe$_2$/MoSe$_2$ bilayers

TL;DR

This study uses multiscale modeling to explore how ferroelectric and piezoelectric domain structures in twisted WX2/MoX2 bilayers trap charge carriers and excitons, revealing angle-dependent trapping behaviors and potential quantum confinement effects.

Contribution

It provides new insights into charge and exciton trapping mechanisms in twistronic WX2/MoX2 bilayers, highlighting the role of domain structures and twist angles in quantum confinement.

Findings

Electrons and holes are trapped at opposite corners of domain walls in 2H bilayers.

Deep traps for interlayer excitons are found at XX corners with 30 meV depth.

In 3R bilayers, domains act as quantum boxes with 130 meV depth for twist angles less than 1 degree.

Abstract

Twistronic van der Waals heterostrutures offer exciting opportunities for engineering optoelectronic properties of nanomaterials. Here, we use multiscale modeling to study trapping of charge carriers and excitons by ferroelectric polarisation and piezoelectric charges by domain structures in twistronic WX$_2$/MoX$_2$ bilayers (X=S,Se). For almost aligned 2H-type bilayers, we find that holes and electrons are trapped in the opposite -- WMo and XX (tungsten over molybdenum {\it versus} overlaying chalcogens) -- corners of the honeycomb domain wall network, swapping their position at a twist angle $0.2^{\circ}$, with XX corners providing $30$\,meV deep traps for the interlayer excitons for all angles. In 3R-type bilayers, both electrons and holes are trapped in triangular "3R stacking" domains, where WX$_2$ chalcogens set over MoX$_2$ molybdenums, which act as $130$\,meV deep quantum boxes for interlayer excitons for twist angles $\lesssim 1^{\circ}$, for larger angles shifting towards domain wall network XX stacking sites.