Electronic Bands and Dielectric Functions of In0.5Tl0.5I Solid State Solution with Structural Defects

Abstract

We investigate an influence of the crystal structure imperfections on the electronic properties and dielectric functions of the In0.5Tl0.5I semiconductor in the frame of the density functional theory calculations. The tensor of electron effective mass m^{*}_{ij} for the InI, In0.5Tl0.5I and TlI crystals has been calculated for the valence and conduction bands at different K-points of the Brillouin zone. The dielectric functions ε(hν) of the imperfect crystals based on In0.5Tl0.5I solid state solution with iodine vacancy and a thallium interstitial atom were calculated taking into consideration the inter-band and intra-band electron transitions. The studies of the imperfect crystals reveal increased low-frequency and stationary electron conductivity with anisotropy resulted from the anisotropy of the electron effective mass tensor. Our findings explain the origin of crucial changes in the band structure by formation of the donor half-occupied levels close to the unoccupied conduction bands due to the crystal structure defects, i.e., iodine vacancy or a thallium interstitial atom. It has been shown that in the case of real crystals, in particular metal-halides, the proper consideration of defects in quantum-chemical calculations results in a better matching with experimental data and, opposite to the perfect structure calculations, gives opportunities to explain the observed phenomena.