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

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 (μ-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 μ-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 Γ 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.

10 pages, 4 figures; + 14 pages, 8 figures in supplementary

References in corpus (2)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Accurate ionic forces and geometry optimisation in linear scaling density-functional theory with local orbitals

Cited by in corpus (4)

• Interlayer Exciton Optoelectronics in a 2D Heterostructure p-n Junction
• Imaging of interlayer coupling in van der Waals heterostructures using a bright-field optical microscope
• Sub-bandgap voltage electroluminescence and magneto-oscillations in a WSe2 light-emitting van der Waals heterostructure
• Odd-integer quantum Hall states and giant spin susceptibility in p-type few-layer WSe2