Computational Study of Structural and Spectroscopic Properties of Doped ZnSe for IR LEDs

Abstract

ZnSe is a hard and intrinsic semiconductor material with a naturally occurring hexagonal or cubic structure. It is potential material for optical devices in the visible and infrared regions due to its large direct band gap of 2.7 eV and strong exciton binding energy. The band gap of ZnSe can be modified to an optimal value in order to properly implement this semiconductor's properties for a specific application. The present research work focuses to investigate the structural and electronic properties as well as absorption coefficient of Mn-doped ZnSe materials in cubic and hexagonal phases using CASTEP numerical coding. Optimized lattice constants are used to construct supercell 2×2×2 for cubic and 1×2×2 for hexagonal supercells to explore the effect of Mn-dopant on structural and optical behavior of ZnSe. The GGA-PBE functional with ultra-soft pseudo-potential for cubic and OTFG-ultrasoft pseudopotential for hexagonal configurations is used for non-spin-polarized calculations. Direct band gap of 0.372eV from cubic and 0.912eV from hexagonal are observed for pure ZnSe supercell, whereas the Fermi level resides between the conduction band and valence band. The energy gap 0.109eV, 0.183eV, and 0.129eV for cubic and energy gap 0.349eV, 0.078eV, 0.087eV for hexagonal structure are observed for one, two and three atoms Mn doped ZnSe which is decreased due to presence of Mn impurity atoms. The absorption spectral peak at 2.6×105 cm-1 for pure ZnSe and 1.28×105 cm-1 , 2×105 cm-1 and 1.96×105 cm-1 are observed on introducing Mn as dopant in ZnSn. Reflectivity, dielectric function, refractive index, conductivity and loss function are decreased with increase in the number of Mn-dopant atoms in ZnSe structure for both cubic and hexagonal phase. The calculated results showed interband absorption due to presence of Mn impurities.