The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. Here we report the determination of band offsets in the heterostructures of transition metal dichalcogenides by using microbeam X-ray photoelectron spectroscopy and scanning tunnelling microscopy/spectroscopy. We determine a type-II alignment between MoS2 and WSe2 with a valence band offset value of 0.83 eV and a conduction band offset of 0.76 eV. First-principles calculations show that in this heterostructure with dissimilar chalcogen atoms, the electronic structures of WSe2 and MoS2 are well retained in their respective layers due to a weak interlayer coupling. Moreover, a valence band offset of 0.94 eV is obtained from density functional theory, consistent with the experimental determination. The alignment of the bandgap of adjacent materials in a heterostructure largely determines the electronic properties of a device. Here, the authors measure the conduction and valance band offsets at the interface between two two-dimensional materials: molybdenum disulphide and tungsten diselenide.

/pdf/determination-of-band-alignment-in-the-single-layer-mos2-5373xmt2x8.pdf

Determination of band alignment in the single-layer MoS2/WSe2 heterojunction

This paper describes the electronic energy levels of semiconductor heterostructures within the envelope function scheme. Quantum well and superlattice electronic states are calculated and discussed, especially the in-plane dispersion relations. The Coulombic bound states in heterostructures (impurities, excitons) are then discussed. Finally, we present a brief overview of the effect of a static electric field on the carrier and exciton energy levels in semiconductor quantum wells.

Electronic states in semiconductor heterostructures

Heterojunction band offset engineering

The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. Here we report the determination of band offsets in the heterostructures of transition metal dichalcogenides by using microbeam X-ray photoelectron spectroscopy and scanning tunnelling microscopy/spectroscopy. We determine a type-II alignment between MoS2 and WSe2 with a valence band offset value of 0.83 eV and a conduction band offset of 0.76 eV. First-principles calculations show that in this heterostructure with dissimilar chalcogen atoms, the electronic structures of WSe2 and MoS2 are well retained in their respective layers due to a weak interlayer coupling. Moreover, a valence band offset of 0.94 eV is obtained from density functional theory, consistent with the experimental determination.

Band Alignment in the Single-Layer MoS2/WSe2 Heterojunction

It is argued that the absolute hydrostatic deformation potentials recently calculated for tetrahedral semiconductors with the linear muffin-tin-orbital method must be screened by the dielectric response of the material before using them to calculate electron-phonon interaction. This screening can be estimated by using the midpoint of an average dielectric gap evaluated at special (Baldereschi) points of the band structure. This dielectric midgap energy (DME) is related to the charge-neutrality point introduced by Tejedor and Flores, and also by Tersoff, to evaluate band offsets in heterojunctions and Schottky-barrier heights. We tabulate band offsets obtained with this method for several heterojunctions and compare them with other experimental and theoretical results. The DME’s are tabulated and compared with those of Tersoff’s charge-neutrality points.

Acoustic deformation potentials and heterostructure band offsets in semiconductors.

X-ray photoemission spectroscopy was used to measure directly the CdTe-HgTe (\ifmmode\bar\else\textasciimacron\fi{}1\ifmmode\bar\else\textasciimacron\fi{}1\ifmmode\bar\else\textasciimacron\fi{}1) heterojunction valence-band discontinuity (${\ensuremath{\Delta}E}_{v}$) with the result ${\ensuremath{\Delta}E}_{v}=0.35\ifmmode\pm\else\textpm\fi{}0.06$ eV. On the basis of the frequently applied common-anion rule, it has generally been assumed that ${\ensuremath{\Delta}E}_{v}$ would be small; the large value of ${\ensuremath{\Delta}E}_{v}$ will affect predicted CdTe-HgTe heterojunction and superlattice properties. In conjunction with recent ${\ensuremath{\Delta}E}_{v}$ measurements on the $\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}\ensuremath{-}{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$ heterojunction system, the large ${\ensuremath{\Delta}E}_{v}$ result for the CdTe-HgTe (\ifmmode\bar\else\textasciimacron\fi{}1\ifmmode\bar\else\textasciimacron\fi{}1\ifmmode\bar\else\textasciimacron\fi{}1) heterojunction provides direct experimental evidence in contradiction to the common-anion rule for lattice-matched heterojunction interfaces.

Steven P. Kowalczyk

Papers

CdTe-HgTe (¯1¯1¯1) Heterojunction Valence-Band Discontinuity: A Common-Anion-Rule Contradiction