The indirect to direct band gap transition in multilayered MoS2 as predicted by screened hybrid density functional theory

Abstract

Molybdenite (MoS2) undergoes a transition from an indirect to direct gap semiconductor exhibiting strong photoluminescence when confined in a 2D monolayer. We investigate the effect of interlayer interactions on the band structure and density of states using the screened hybrid functional of Heyd, Scuseria, and Ernzerhof. We show that for the bulk and monolayer systems, our short-range screened hybrid functional produces band gaps in good agreement with experiment. Our functional includes only interlayer interactions of non-van der Waals origin, predicts properties consistent with recent experiments, and provides predictions for few-layered systems.

Surface Recombination Limited Lifetimes of Photoexcited Carriers in Few-Layer Transition Metal Dichalcogenide MoS2

“…There is a possibility that higher energy quantum confined states in our few-layer samples could be occupied by hot or thermally excited carriers. However, even in the 10-layer sample the second confined state is estimated to be 50-100 meV higher in energy 47 and is, therefore, not expected to have significant carrier population. Also, we see no temperature dependence in the measured lifetimes and this indicates that there is no significant error made in ignoring carrier spilling into the higher quantum confined states.…”

“…This procedure is equivalent to assuming a spatially varying defect structure in a more formal calculation technique such as the one presented by Wang et al 25 . This procedure also assumes that the carriers are mobile in the direction normal to the plane of the layers, an assumption that seems to be justified by the large splittings of the energy subbands observed in the conduction band minima and the valence band maxima in few layer MoS 2 in calculations 47 . The envelope of the electron (or hole) wavefunction of the lowest quantum confined state (confined in the direction perpendicular to the layers) can be obtained using the effective mass approximation (and assuming a discrete space),…”

“…Two dimensional (2D) transition metal dichalcogenides (TMDs) are proving to be interesting matearXiv:1510.08563v2 [cond-mat.mes-hall] 2 Nov 2015 rials for a variety of different low-cost optoelectronic device applications, including photodetectors, light-emitting diodes, and, more recently, lasers [1][2][3][4][5][6][7][8][9][10][11] . Indirect bandgap few layer and bulk TMDs are well suited for high quantum efficiency photodetection applications because of their large optical absorption coefficients and long photoexcited carrier lifetimes [12][13][14] .…”

Electrons and phonons in single layers of hexagonal indium chalcogenides fromab initiocalculations

“…The HSE06 band gap is expected to underestimate the quasiparticle band gap by no more than 10%, 35 and is known to be accurate in 2D materials. 36 The effective masses at the high-symmetry points in the conduction band are summarized in Table II. The effective mass is isotropic at the Γ and K points, but not at M. We note that the effective mass is quite sensitive to the fitting range.…”

Vibrational and optical properties of MoS2: From monolayer to bulk

“…This issue has been theoretically addressed either through LDA/GGA calculations [163,27,28,31], or the GW method [144]. The effect of hydrostatic pressure on the vibrational, electronic, and optical properties of bulk, multi-, and single layer MoS 2 was investigated by Nayak et al [33,34] by combining various experiments (high resolution transmission electron microscopy, electrical resistance measurements, laser Raman spectroscopy, synchrotron X-ray diffraction experiments under high-pressure) with DFT calculations.…”