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. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Vijay Kumar

Center for Informatics

Deb A.K.

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Shiv Nadar University

Physica Status Solidi (B) Basic Research

We study the structural stability and electronic properties of new classes of DNA-like inorganic double helices of the type A2B2XY (A = Si-Pb, B = Cl-I, and XY = PN and SiS) by employing first principles density functional theory (DFT) calculations including van der Waals interactions. In these quaternary double helices PN or SiS forms the inner helix while the AB helix wraps around the inner helix and the two are interconnected. We find that the bromides and iodides of Ge, Sn, and Pb as well as Pb2Cl2PN form structurally stable double helices while Ge2I2SiS as well as bromides and iodides of Sn and Pb have stable double helices. The atomic structures of different double helices have been analyzed in detail to understand the stability of these systems as there is up to about 80\% difference in the interatomic distances in the two helices which is remarkable. Also in these new classes of double helices there is polar covalent bonding in the inner helix due to heteroatoms. We have calculated the DDEC6 partial atomic charges and bond orders which suggest strong covalent bonding in the inner helix. The electronic structure reveals that these double helices are semiconducting and in many cases the band gap is direct. Furthermore, we have studied the effects of doping and found that hole doping is the most appropriate way to tuning their electronic properties. © the Owner Societies 2018.

Fulltext

Physical Chemistry Chemical Physics

Atomic structure and electronic properties of A2B2XY (A = Si-Pb, B = Cl-I, and XY = PN and SiS) inorganic double helices: First principles calculations

Ab initio calculations on CsSnX3 perovskites and mixed halides CsSn(XxY 1-x)3, X and Y = I, Cl, and Br, show that all of them have a direct band gap of ∼1 eV which can be tuned by varying the compositions of X and Y. The optimized supercells are tetragonal, orthorhombic or monoclinic. The top of the valence band arises from hybridization of Sn 4s and halogen p valence orbitals while the bottom of the conduction band has predominantly Sn p character. Similar to organo-metallic lead halides this is expected to facilitate p-p optical transitions that are highly favourable for photoabsorption. Our results suggest that these inorganic perovskites have the desired features to achieve high efficiency of photo-response with appropriate combination of halogens. © 2015 Author(s).

AIP Advances

Ab initio design of CsSn(XxY 1-x)3 (X and y = Cl, Br, and I) perovskites for photovoltaics

Applied Physics Letters

Giant piezoelectricity of monolayer group IV monochalcogenides: SnSe, SnS, GeSe, and GeS

The Journal of Physical Chemistry C

Large Enhancement and Tunable Band Gap in Silicene by Small Organic Molecule Adsorption

RSC Advances

Strain engineering of WS2, WSe2, and WTe2

Computational prediction of two-dimensional group-IV mono-chalcogenides

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