Structural, electronic and optical Properties of chalcopyrite type Semiconductors

Abstract

A theoretical study of the structural, electronic and optical properties of a series of group I−III −V I2, II−IV −V2, I−III2−V I4, II−III2−V I4, I2−III −V I4 and
few substituted chalcopyrite type semiconductors are presented in this thesis. Systems studied are AgAlM2 (M = S, Se, Te), CuInSe2, ZnSnX2 (X = P, As, Sb), AAl2Se4 (A
= Ag, Cu, Cd, Zn), CuIn2X4 (X = S, Se), CdGa2X4 (S, Se, Te), CdIn2Te4, Cu2InSe4, ZnXIn2Te4 (X = O, Mn), CdMGa2S4 (X = Ag, Al), CuNaIn2S4, CuLiIn2Se4 and Cu2InXSe4 (X = Al, Ga) substituted chalcopyrite semiconductors. Our study is density functional theory (DFT) based first principle calculation within the frame work of tight binding linear muffin-tin orbital (TB-LMTO) basis.The structural parameters such as lattice constants, anion displacement, tetragonal distortion and bond lengths are calculated by proper energy minimization. Bulk modulus of all the systems except ZnXIn2Te4 (X = O, Mn), are calculated by extended Cohen
formula. Our study shows an inverse proportionality relation between lattice constant and bulk modulus for these systems. Band structure and total density of states (TDOS) of all
the systems under study show that they are direct band gap semiconductors. AAl2Se4 (A = Ag, Cu), CuIn2X4 (X = S, Se) and Cu2InSe4 are p-type direct band gap semiconductors
whereas CdMGa2S4 (X = Ag, Al) and ZnXIn2Te4 (X = O, Mn) are n-type direct band gap semiconductors. Our calculated results agree well with the available experimental
results. Our study of partial density of states (PDOS) reveals that the contribution to upper valence band comes from the cation d and anion p hybrid orbitals in case of group I −III −V I2, I −III2 −V I4 , I2 −III −V I4 and their substituted chalcopyrites.