Structural and optical properties of flash evaporated AgInTe2thin films

Abstract

Thin films of AgInTe2 were prepared on quartz substrates by a flash evaporation technique at substrate temperature ~303 K. The compositions of both the bulk and thin films, with thickness (~208–350 nm), were checked using energy dispersive X-ray spectroscopy (EDX). X-ray diffraction (XRD) measurements showed that AgInTe2 compound is characterized by a tetragonal structure while the as deposited films have amorphous nature. On annealing at 423 and 573 K (for two hours and under vacuum ~10−3 Pa), the films were identified to be single-phase, polycrystalline with a preferred (112) orientation. The optical properties of the films were investigated using spectrophotometric measurements of transmittance and reflectance at normal incidence in the wavelength range (~500–2500 nm). The refractive index (n) and the absorption index (k) of AgInTe2 were determined from the absolute values of the measured transmittance and reflectance. It was found that both (n) and (k) depend markedly on the temperature of heat treatment. The dispersion of refractive index in AgInTe2 was analyzed using the concept of the single oscillator model. Within this concept some dispersion parameters were determined for as deposited and annealed flash evaporated AgInTe2 films at 423 K for 2 h. The calculated values of β indicated that AgInTe2 films belong to ionic class. The ratio of the free carrier concentration to the effective mass (N/m*) were, also determined. The analysis of the absorption coefficient indicated that, this ternary chalcopyrite compound has three allowed direct transitions corresponding to three energies gaps Eg 1, Eg 2 and Eg 3. The crystal field (Δcf), the spin orbit (Δso) and the deformation potential (b) were calculated for both as deposited and annealed flash InAgTe2 films at ~423 K for 2 h.