Exciton band structure in layered MoSe2: from a monolayer to the bulk limit

TL;DR

This study investigates how excitonic properties and band structures evolve in MoSe2 from monolayer to bulk using optical spectroscopy, revealing layer-dependent shifts, linewidth changes, and unique resonance features.

Contribution

It provides detailed experimental insights into the layer-dependent exciton band structure and optical responses of MoSe2, including the identification of Fano resonance in monolayer.

Findings

Excitonic transitions shift with layer thickness.

Monolayer MoSe2 exhibits a bright ground state exciton.

Fano-type resonance observed in monolayer optical response.

Abstract

We present the micro-photoluminescence ($\mu$PL) and micro-reflectance contrast spectroscopy studies on thin films of MoSe2 with layer thicknesses ranging from a monolayer (1L) up to 5L. The thickness dependent evolution of the ground and excited state excitonic transitions taking place at various points of the Brillouin zone is determined. Temperature activated energy shifts and linewidth broadenings of the excitonic resonances in 1L, 2L and 3L flakes are accounted for by using standard formalisms previously developed for semiconductors. A peculiar shape of the optical response of the ground state (A) exciton in monolayer MoSe2 is tentatively attributed to the appearance of Fano-type resonance. Rather trivial and clearly decaying PL spectra of monolayer MoSe2 with temperature confirm that the ground state exciton in this material is optically bright in contrast to a dark exciton ground state in monolayer WSe2.