Bandgap engineering in semiconducting one to few layers of SnS and SnSe

Abstract

Ab initio calculations on one, two, and three layers of SnS and SnSe compound semiconductors show that they all have indirect band gap similar to bulk and it varies in the range of ∼0.5–1.6 eV within the generalized gradient approximation due to quantum confinement as well as structural relaxations. In two‐dimensional structures, the difference between the direct and the indirect band gap is very low and in the case of a SnS bilayer, this difference is minimum. Further, the band gaps calculated with HSE06 functional are in good agreement with the experimental results available for bulk and single layer. The total and projected densities of states show that the top of the valence band arises from the hybridization of Sn 5s and chalcogen p valence orbitals while the bottom of the conduction band has predominantly Sn 5p character. The effective mass of electrons and holes are found to be small. These features are similar to the recently discovered perovskite materials for photovoltaics with high efficiency and suggest that SnS and SnSe layered materials are also promising for photovoltaics. Further calculations on bulk and layers of GeS and GeSe are reported and the results are compared with those of SnS and SnSe structures.

Photoacoustic and modulated reflectance studies of indirect and direct band gap in van der Waals crystals

“…No optical transition in MR spectrum of GeSe can be associated with poor quality of this crystal or no band bending modulation in this sample. Energies found for this couple of compounds are qualitatively consistent with recent theoretical studies of energy gap for these crystals, i.e., replacing smaller S atoms by larger Se atoms the band gap narrows, following the well-known trend in standard semiconductors 57–59 . The quantitative agreement with the previous experimental studies 58 is also quite good, see Table 1.…”

Facile Formation of Nanodisk‐Shaped Orthorhombic SnS Layers from SnS2 Particles for Photoelectrocatalytic Hydrogen Production

“…The E g value changes from 1.7 to 2.1 eV as the thickness scales from 200 nm to 10 nm. The measured band edges are in good agreement with theoretical predictions . The estimated E g values as a function of the SnS layer thickness is shown in Figure d. Ab‐initio study suggests that the increase of the E g values with decreasing the layer thickness is not monotonic but an odd‐even quantum confinement effect due to the interplay of spin‐orbit coupling and anisotropic spin splitting of the energy bands …”

“…The measured band edges are in good agreement with theoretical predictions. [3,43] The estimated E g values as af unction of the SnS layer thickness is showni nF igure 2d.A b-initio study suggestst hat the increase of the E g values with decreasingthe layer thickness is not monotonic but an odd-even quantum confinement effect due to the interplay of spin-orbit coupling and anisotropic spin splitting of the energy bands. [3] To study the thickness-dependent electrical properties and energy band edges of the highlyc rystalline SnS samples, Mott-Schottkya nalyses were conducted.…”

Theoretical prediction of structural, mechanical, and electronic properties of Janus GeSnX2 (X = S, Se, Te) single-layers

“…The E coh of GeSnX 2 is form 3.74 to 4.42 eV per atom, which is comparable with that of the group IV monochalcogenides. 43,44 We next analyze the vibrational properties of the systems to evaluate their dynamical stability. The phonon dispersion bands of Janus GeSnX 2 are presented in Fig.…”