Direct band gaps in group IV-VI monolayer materials: Binary counterparts of phosphorene

Abstract

We perform systematic investigation on the geometric, energetic and electronic properties of group IV-VI binary monolayers (XY), which are the counterparts of phosphorene, by employing density functional theory based electronic structure calculations. For this purpose, we choose the binary systems XY consisting of equal numbers of group IV (X = C, Si, Ge, Sn) and group VI elements (Y = O, S, Se, Te) in three geometrical configurations, the puckered, buckled and planar structures. The results of binding energy calculations show that all the binary systems studied are energetically stable. It is observed that, the puckered structure, similar to that of phosphorene, is the energetically most stable geometric configuration. Moreover, the binding energies of buckled configuration are very close to those of the puckered configuration. Our results of electronic band structure predict that puckered SiO and CSe are direct band semiconductors with gaps of 1.449 and 0.905 eV, respectively. Band structure of CSe closely resembles that of phosphorene. Remaining group IV-VI binary monolayers in the puckered configuration and all the buckled monolayers are also semiconductors, but with indirect band gaps. Importantly, we find that the difference between indirect and direct band gaps is very small for many puckered monolayers. Thus, there is a possibility of making these systems undergo transition from indirect to direct band gap semiconducting state by a suitable external influence. Indeed, we show in the present work that seven binary monolayers namely SnS, SiSe, GeSe, SnSe, SiTe, GeTe and SnTe become direct band gap semiconductors when they are subjected to a small mechanical strain (≤ 3 %). This makes nine out of sixteen binary monolayers studied in the present work direct band gap semiconductors. Thus, there is a possibility of utilizing these binary counterparts of phosphorene in future light-emitting diodes and solar cells.

Structural and electronic properties of monolayer group III monochalcogenides

“…It clearly demonstrates that oxides exhibit a distinct character from those of sulphides, selenides, and tellurides. Recently, a similar trend has also been observed in both group IV-VI [19] and group II-VI monolayers [51].…”

“…These investigations resulted in the discovery of many 2D families such as group IV and group III-V binary compounds in honeycomb structure [17]. Very recently, theoretical studies have reported a stable class of single-layer group IV monochalcogenides (Y X, Y = Si, Ge, Sn and X = S, Se, and Te) that are semiconductors with * seymur@unam.bilkent.edu.tr wide band gaps [18][19][20]. Furthermore, a study focused on the structural and electronic properties of these systems reported indirect-direct band gap transitions under small mechanical strain [19].…”

“…Very recently, theoretical studies have reported a stable class of single-layer group IV monochalcogenides (Y X, Y = Si, Ge, Sn and X = S, Se, and Te) that are semiconductors with * seymur@unam.bilkent.edu.tr wide band gaps [18][19][20]. Furthermore, a study focused on the structural and electronic properties of these systems reported indirect-direct band gap transitions under small mechanical strain [19]. Most recently, the transition from semiconductor to metal has been achieved when a large compressive strain was applied to monolayers of GeX and SnX [21].…”

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

“…As a two‐dimensional (2D) material with an analogous structure as black phosphorus, yet with a finite band gap unlike graphene, tin sulfides have gained considerable attention among the family of two‐dimensional (2D) materials . Among tin sulfides, SnS (tin monosulfide, Herzenbergite) is known as a potential candidate for solar energy utilization due to its fascinating electronic properties such as direct optical band gap (1.4–1.7 eV) and a high absorption coefficient (>10 4 cm −1 ), in addition to the fact that it is earth‐abundant, non‐toxic and air stable .…”

“…This 2D nature of the SnS layer renders only a weak interaction between neighboring layers via van der Waals interactions, which allows easy separation and fabrication of layered composite structures with highly disparate atomic layers to create a wide range of van der Waals (vdWs) heterostructures without any constraints of lattice match and compatibility. Therefore, the processability of SnS combined with its extraordinary physical and chemical properties makes it a perfect model system in exploring new 2D properties …”