Prominent room temperature valley polarization in WS2/graphene heterostructures grown by chemical vapor deposition

TL;DR

This study demonstrates that WS2/graphene heterostructures exhibit high room temperature valley polarization due to efficient charge transfer and reduced depolarization, surpassing other encapsulation methods, with implications for valleytronic devices.

Contribution

It reveals that WS2/graphene heterostructures maintain high valley polarization at room temperature, highlighting the role of material interactions in depolarization mechanisms.

Findings

Room temperature polarization reaches 24% in WS2/Gr heterostructures.

WS2/Gr heterostructures show nearly temperature-independent depolarization.

Significant polarization variation observed at 4K depending on heterostructure configuration.

Abstract

We examine different cases of heterostructures consisting of WS2 monolayers grown by chemical vapor deposition (CVD) as the optically active material. We show that the degree of valley polarization of WS2 is considerably influenced by the material type used to form the heterostructure. Our results suggest the interaction between WS2 and graphene (WS2/Gr) has a strong effect on the temperature dependent depolarization (i.e. decrease of polarization with increasing temperature), with polarization degrees reaching 24% at room temperature under near-resonant excitation. This contrasts to hBN- encapsulated WS2, which exhibits a room temperature polarization degree of only 11%. The observed low depolarization rate in WS2/Gr heterostructure is attributed to the nearly temperature independent scattering rate due to phonons and fast charge and energy transfer processes from WS2 to graphene. Significant variations in the degree of polarization are also observed at 4K between the different heterostructure configurations. Intervalley hole scattering in the valence band proximity between the K and {\Gamma} points of WS2 is sensitive to the immediate environment, leading to the observed variations.