Optical Characteristics of Thermally Evaporated Thin a-(Cu2ZnGe)50−xSe50+x Films

Abstract

This article is allocated to study optical characteristics of a-(Cu2ZnGe)50−xSe50+x, CZGSe, ( 0 ≤ x ≤ 20 at wt % ) films. The amorphous nature of films was affirmed via X-ray diffractograms. energy-dispersive X-ray spectroscopy confirmed the matching between selected compositional element percentages and those measured for all films. Many optical properties and parameters of CZGSe films were studied using UV–vis-INR spectroscopic transmission and reflection measurements. The envelope methods have been successfully applied on the measured transmission spectra according to Swanepoel technique, along with reflection spectra in accordance with Minkov method. Obtained results based on Swanepoel analysis are in excellent agreement with those inferred from Minkov method. A clear blueshift of the absorption edge was observed from 854 nm to 720 nm, in accordance with the increasing optical bandgap energy values from 1.456 eV to become 1.722 eV, as Se-content increases from 50 to 70 at wt%. The electronic transitions of (Cu2ZnGe)50−xSe50+x films arose from allowed indirect transitions. This observed energy gap increases was interpreted according to the Mott and Davies model. The absorption coefficient values have been estimated and discussed, it is found to be larger than 10−4 cm−1. All discussed parameters strongly depend on the Se-concentration. The bonding strength between the elements of samples strongly affects the optical properties.