Modulation of band gap and optical response of layered MoX2 (X = S, Se, Te) for electronic and optoelectronic applications

Abstract

Motivated by the fascinating behavior of monolayer MoX2 (X = S, Se, Te), we have reported the structural, phonon dispersions relations, electronic and optical properties for monolayer to quadlayer of MoX2 (X = S, Se, Te) by employing ab-initio calculations. The optimized lattice parameters, bond angle and bond length of layered MoX2 (X = S, Se, Te) increases in the order of MoS2 < MoSe2 < MoTe2 which are in good agreement with earlier reported results. The dynamic stability is confirmed by cohesive energy and phonon modes with positive frequency in phonon dispersion calculations. The observed frequency gap between high and low frequency optical mode depicts the utility of layered MoX2 (X = S, Se, Te) in selective transmission of higher frequency range. The electronic band structure of layered MoX2 (X = S, Se, Te) shows semiconducting character with degeneracy as per number of layers. However, the noticeable change in indirect band gap energy compared to direct band gap energy is observed from quadlayer to monolayer which shows interactions of d orbital in MoX2 (X = S, Se, Te). The polarizability of layered MoX2 (X = S, Se, Te) increases with the increasing number of layers. The refractive index also increases with the number of layers and reaches up to 4.34, 4.11 at energy 2.45 eV, 2.05 eV, respectively in visible region and 4.12 at energy 1.45 eV in IR region of electromagnetic spectrum for MoS2, MoSe2 and MoTe2 quadlayer, respectively. The maximum reflectivity responses of 49%, 58% and 68% are obtained for MoS2, MoSe2 and MoTe2 quadlayer, respectively in the C band of UV region.