Optical and calorimetric studies of Ge–Sb–Se glasses

• Published in: Journal of non-crystalline solids 2000-03, Vol.265 (1), p.157-166
• Main Authors: Wakkad, M.M, Shokr, E.Kh, Mohamed, S.H
• Format: Article
• Language: English
• Subjects: Amorphous semiconductors; glasses; Amorphous semiconductors; glasses; nanocrystalline materials; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity); Optical constants: refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; Optical properties of specific thin films; Physics
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/S0022-3093(99)00882-0

Optical properties of amorphous Ge x Sb 40 − x Se 60 ( x=22.5, 25, 27.5, 30 and 32.5 at.%) thin films prepared by electron beam evaporation have been measured in the visible and near-infrared spectral region. The variations of the electronic energy gap ( E g) with composition are discussed on the basis of both the overall mean bond energy and the topological model based on the structural dimensionality considerations. A pronounced peculiarity (maximum or minimum) appeared at around the same value of the average coordination number ( Z)=2.65 for all the compositional dependencies of electronic energy gap, high frequency dielectric constant, optical relaxation time and the dispersion parameters, is attributed to a topological phase transition from two-dimensional (2D) layer type to three-dimensional (3D) cross-linked network structures in the present glassy thin films. This confirms the suitability of structural topological model to explain the compositional dependencies of the physical parameters, not only for bulk glasses but also for thin films evaporated from them. These results are supported by volumetric and the calorimetric measurements.