Thickness and twist angle dependent interlayer excitons in metal monochalcogenide heterostructures

TL;DR

This study reveals tunable interlayer excitons in metal monochalcogenide heterobilayers, with properties influenced by thickness and twist angle, highlighting their potential for exploring correlated electronic phases.

Contribution

It demonstrates the existence of adjustable interlayer excitons in gamma-InSe/e-GaSe heterobilayers, with detailed analysis of their lifetimes, separation, and twist angle dependence.

Findings

Interlayer excitons exhibit longer lifetimes than intralayer ones.

Exciton emission energy is tunable by layer thickness and twist angle.

Interfacial Se separation closely matches the exciton electron-hole separation.

Abstract

Interlayer excitons, or bound electron-hole pairs whose constituent quasiparticles are located in distinct stacked semiconducting layers, are being intensively studied in heterobilayers of two dimensional semiconductors. They owe their existence to an intrinsic type-II band alignment between both layers that convert these into p-n junctions. Here, we unveil a pronounced interlayer exciton (IX) in heterobilayers of metal monochalcogenides, namely gamma-InSe on epsilon-GaSe, whose pronounced emission is adjustable just by varying their thicknesses given their number of layers dependent direct bandgaps. Time-dependent photoluminescense spectroscopy unveils considerably longer interlayer exciton lifetimes with respect to intralayer ones, thus confirming their nature. The linear Stark effect yields a bound electron-hole pair whose separation d is just (3.6 \pm 0.1) {\AA} with d being very close to dSe = 3.4 {\AA} which is the calculated interfacial Se separation. The envelope of IX is twist angle dependent and describable by superimposed emissions that are nearly equally spaced in energy, as if quantized due to localization induced by the small moir\'e periodicity. These heterostacks are characterized by extremely flat interfacial valence bands making them prime candidates for the observation of magnetism or other correlated electronic phases upon carrier doping.