On the band gap location and core spectra of orthorhombic IV–VI compounds SnS and SnSe

Abstract

While the orthorhombic IV–VI compounds show the typical layered behavior of that crystallography, we show that the presence of sulphur induces important changes to the band gap behaviour: both in its location, and in its character as well. Our modelling of tin sulfide (SnS) and tin selenide (SnSe), performed within an ab initio density‐functional theory (DFT) with a FP‐LAPW method, shows that the spin–orbit interaction produces slight splittings of bands in both compounds, especially in the conduction band, which are in very good agreement with measured values of the core spectra. In addition to these splittings, for SnS we found the novel feature that the spin–orbit relocates the band gap in the BZ, while it does not affect that of SnSe. Furthermore, several aspects of the crystals anisotropy may be explained upon our results on the hybridized band structure, the density of states (DOS) and the optical spectra (complex dielectric function and absorption coefficient). We satisfactorily compare our results with those available in the literature. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Quasiparticle band structures and interface physics of SnS and GeS

“…From the band structure it can be seen that there are nearby competing extrema in both the valence and conduction bands. 11,19 Because these competing band extrema are close in energy, different band gaps can be obtained depending on the choice of exchangecorrelation functional and whether or not the band structure is computed at the experimental or the theoretical values for the lattice constants. For this reason we do not make comparison of these gaps to other published results.…”

Grain size and lattice parameter's influence on band gap of SnS thin nano-crystalline films

“…Since the lattice parameter 'b' showed insignificant variation with thickness in samples grown on glass and ITO substrates, we conclude that 'b' lattice parameter does not contribute to the variation in band gap. Also, its contribution is only along the Γ → Y direction of the BZ [7] where the "energy difference" (difference in valence band maximum and conduction band minimum) is too large to be considered as energy band gap associated with SnS.…”

Optoelectronic properties of single-layer, double-layer, and bulk tin sulfide: A theoretical study

“…This approach has been shown to describe SnS with satisfactory (albeit fortuitous) accuracy compared to experiment 12 and with much less computational effort compared to approaches that aim at higher accuracy, for instance with the use of hybrid functionals. 12,30,32,45 Thus, it provides a reasonable way to address the elastic properties of the material in the various forms we considered here. On the other hand, LDA typically underestimates the fundamental band gap of semiconductors and insulators.…”

“…13,[16][17][18][19][20] General strategies for tuning the properties of the material, also relevant to the fabrication of novel electronic devices, include the use of atomically thin compounds [21][22][23][24] and the application of mechanical strain. [25][26][27] SnS has been extensively investigated in its bulk form [28][29][30][31][32][33][34] but few-layer and single-layer structures remain largely unexplored. 8,35 The measured properties of SnS samples depend on the synthesis route.…”

“…9,[36][37][38][39] Theory and atomistic simulation can contribute significantly in clarifying how the properties of SnS and other layered semiconductors depend on the atomicscale structural features. 12,25,27,30,32,40,41 Here, we use firstprinciples calculations based on density functional theory and the GW approximation to the electron self-energy to study trends in the electronic and optical properties of model single-layer, double-layer, and bulk structures of SnS. Specifically, we calculate the indirect and direct band gaps and the dielectric functions, which depend on the number of layers and the separation between them: the direct band gap narrows in going from single-layer to bulk SnS or by applying tensile strain along the layer stacking direction.…”