Ultrafast Charge Transfer in Atomically Thin MoS2/WS2 Heterostructures

TL;DR

This paper reports the first experimental observation of ultrafast hole transfer within 50 femtoseconds in MoS2/WS2 heterostructures, highlighting their potential for advanced optoelectronic applications.

Contribution

It provides the first experimental evidence of ultrafast charge transfer in atomically thin MoS2/WS2 heterostructures using femtosecond spectroscopy.

Findings

Hole transfer occurs within 50 fs after excitation.

Ultrafast charge transfer enables potential 2D optoelectronic devices.

Supports theoretical predictions of efficient charge separation in MX2 heterostructures.

Abstract

Van der Waals heterostructures have recently emerged as a new class of materials, where quantum coupling between stacked atomically thin two-dimensional (2D) layers, including graphene, hexagonal-boron nitride, and transition metal dichalcogenides (MX2), give rise to fascinating new phenomena. MX2 heterostructures are particularly exciting for novel optoelectronic and photovoltaic applications, because 2D MX2 monolayers can have an optical bandgap in the near-infrared to visible spectral range and exhibit extremely strong light-matter interactions. Theory predicts that many stacked MX2 heterostructures form type-II semiconductor heterojunctions that facilitate efficient electron-hole separation for light detection and harvesting. Here we report the first experimental observation of ultrafast charge transfer in photo-excited MoS2/WS2 heterostructures using both photoluminescence mapping and femtosecond (fs) pump-probe spectroscopy. We show that hole transfer from the MoS2 layer to the WS2 layer takes place within 50 fs after optical excitation, a remarkable rate for van der Waals coupled 2D layers. Such ultrafast charge transfer in van der Waals heterostructures can enable novel 2D devices for optoelectronics and light harvesting.