Effect of Bi addition on the physical and optical properties of Ge20Te74-xSb6Bix (x = 2, 4, 6, 8, 10) thin films deposited via thermal evaporation

Chalcogenide materials in different forms (bulk, thin film, nanocrystals etc.) are finding applications in various sectors e.g. in infrared optics for communication, imaging, limiting, remote sensing and laser power delivery etc. Here we report the synthesis of Ge20Te74-xSb6Bix (x = 2, 4, 6, 8, 10) chalcogenide alloys and estimation of some physical properties i.e. average coordination number, lone pair electron, number of constraints, heat of atomization, compactness, glass transition temperature etc. The transmission spectra of thin films have been acquired using UV-Visible-NIR spectrophotometer in the wavelength range of 400 nm-2600 nm. Various optical properties like refractive index, extinction coefficient, optical band gap, real and imaginary parts of dielectric constants have been evaluated using the transmission spectrum. The optical band gap of the synthesized samples has shown similar trend with the band gap determined theoretically. The average coordination number has been found to increase whereas the number of lone pair electron is found to decrease. This shows that the system under investigation is moving towards more rigid region as per constraint theory. The heat of atomization energy and theoretical band gap has also shown variation with the addition of Bi content. The tailoring of band gap along with an increase in rigidity may lead to an increase in the domain of technological applications for these alloys.