Band parameters and hybridization in 2D semiconductor heterostructures from photoemission spectroscopy

TL;DR

This paper demonstrates the use of advanced photoemission spectroscopy to accurately measure band parameters and hybridization in 2D semiconductor heterostructures, revealing weak and strong hybridization regions and quantifying band offsets.

Contribution

It introduces a heterostructure design that enables high-resolution {b5}-ARPES measurements of small 2D samples, providing detailed insights into band hybridization and offsets.

Findings

Weak hybridization of bands at K valleys in MoSe2/WSe2 heterobilayers

Stronger hybridization observed at the b0 point, valence band edge remains at K points

Valence band offset measured at 300 meV, interlayer exciton binding energy at least 200 meV

Abstract

Combining monolayers of different two-dimensional (2D) semiconductors into heterostructures opens up a wealth of possibilities for novel electronic and optical functionalities. Exploiting them hinges on accurate measurements of the band parameters and orbital hybridization in separate and stacked monolayers, many of which are only available as small samples. The recently introduced technique of angle-resolved photoemission spectroscopy with submicron spatial resolution ({\mu}-ARPES) offers the capability to measure small samples, but the energy resolution obtained for such exfoliated samples to date (~0.5 eV) has been inadequate. Here, we show that by suitable heterostructure sample design the full potential of {\mu}-ARPES can be realized. We focus on MoSe2/WSe2 van der Waals heterostructures, which are 2D analogs of 3D semiconductor heterostructures. We find that in a MoSe2/WSe2 heterobilayer the bands in the K valleys are weakly hybridized, with the conduction and valence band edges originating in the MoSe2 and WSe2 respectively. There is stronger hybridization at the {\Gamma} point, but the valence band edge remains at the K points. This is consistent with the recent observation of interlayer excitons where the electron and hole are valley polarized but in opposite layers. We determine the valence band offset to be 300 meV, which combined with photoluminescence measurements implies that the binding energy of interlayer excitons is at least 200 meV, comparable with that of intralayer excitons.