Insight into the electronic structure of semiconducting ε−GaSe and ε−InSe

Abstract

Metal monochalcogenides (MX ) have recently been rediscovered as two-dimensional materials with electronic properties highly dependent on the number of layers. Although some intriguing properties appear in the few-layer regime, the carrier mobility of MX compounds increases with the number of layers, motivating the interest in multilayered heterostructures or bulk materials. By means of angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory calculations, we compare the electronic band structure of bulk -GaSe and -InSe semiconductors. We focus our attention on the top valence band of the two compounds along main symmetry directions, discussing the effect of spin-orbit coupling and contributions from post-transition-metal (Ga or In) and Se atoms. Our results show that the top valence band at point is dominated by Se p z states, while the main effect of Ga or In appears more deeply in binding energy, at the Brillouin zone corners, and in the conduction band. These findings explain also the experimental observation of a hole effective mass rather insensitive to the post-transition metal. Finally, by means of spin-resolved ARPES and surface band structure calculations we describe Rashba-Bychkov spin splitting of surface states in -InSe.

Raman Scattering and Exciton Photoluminescence in Few-Layer GaSe: Thickness- and Temperature-Dependent Behaviors

“…The uncontrollable mechanical defects of the crystal structure, that are mainly losses of chalcogen, are supposed to arise during mechanical exfoliation and deposition on a substrate . Deep defect states below the edge of the conductivity band are known to originate from the chalcogen deficiency (i.e., vacancies V Se and V S ). ,, On the other hand, since 2D GaSe is a p-type semiconductor where the Fermi level is located just at the maximum of the valence band, ,,, the mentioned transitions can only be the recombination from deep defect states below the minimum of the conductivity band of the optical band gap to the valence band maximum.…”

Spin-Orbit Coupling and Spin-Polarized Electronic Structures of Janus Vanadium-Dichalcogenide Monolayers: First-Principles Calculations

“…Rashba SOC can be effectively ameliorated by applying an in-plane biaxial strain to modify chalcogen bonding and intrinsic electric field [16]. In contrast to III-VI double layers or MXY heterostructures with a Rashba splitting deriving from the surface or interface electronic states under applying electric fields [17,18], the Janus TMD monolayers lacking out-of-plane mirror symmetry may present Rashba splitting from internal electric field and strong SOC of heavy chalcogens, which facilitate their application in spintronic devices. Furthermore, Janus TMD monolayers exhibit the transcendental characteristics of large out-of-plane piezoelectric performance, high hydrogen hydrocatalytic capability and broad absorption in solar spectrum, all of which can be attributed to to the imbalanced electron-wave functions between the two sulfur atom-layers.…”