Radiative Pattern of Intralayer and Interlayer Excitons in Two-Dimensional WS2/WSe2 Heterostructure

TL;DR

This study investigates the radiative properties of intralayer and interlayer excitons in WS2/WSe2 heterostructures, revealing the out-of-plane dipole orientation of interlayer excitons through angle-resolved spectroscopy at cryogenic temperatures.

Contribution

It provides direct experimental evidence of the out-of-plane dipole orientation of interlayer excitons in 2D TMDC heterostructures using angle-resolved photoluminescence spectroscopy.

Findings

Interlayer excitons exhibit out-of-plane dipole orientation.

Radiation profile of interlayer excitons resembles in-plane emitters.

Distinct from intralayer excitons and moiré-pattern-induced features.

Abstract

Two-dimensional (2D) heterostructures (HS) formed by transition-metal dichalcogenide (TMDC) monolayers offer a unique platform for the study of intralayer and interlayer excitons as well as moir\'e-pattern-induced features. Particularly, the dipolar charge-transfer exciton comprising an electron and a hole, which are confined to separate layers of 2D semiconductors and Coulomb-bound across the heterojunction interface, has drawn considerable attention in the research community. On the one hand, it bears significance for optoelectronic devices, e.g. in terms of charge carrier extraction from photovoltaic devices. On the other hand, its spatially indirect nature and correspondingly high longevity among excitons as well as its out-of-plane dipole orientation render it attractive for excitonic Bose-Einstein condensation studies, which address collective coherence effects, and for photonic integration schemes with TMDCs. Here, we demonstrate the interlayer excitons' out-of-plane dipole orientation through angle-resolved spectroscopy of the HS photoluminescence at cryogenic temperatures, employing a tungsten-based TMDC HS. Within the measurable light cone, the directly-obtained radiation profile of this species clearly resembles that of an in-plane emitter which deviates from that of the intralayer bright excitons as well as the other excitonic HS features recently attributed to artificial superlattices formed by moir\'e patterns.