The low-frequency Raman spectra and nanostructure of As-Se-S and As-Se-Te chalcogenide semiconductors doped by samarium

Abstract

ABSTRACT It has been established that the Raman scattering (RS) of chalcogenide glass–like semiconductors (CGS) materials As-Se-S and As-Se-Te at frequencies below 100 cm -1 consists of two parts: first - which the intensity with increasing frequency up to 30 ÷ 40 cm -1 decreases (quasi-elastic scattering); second - which have been observed a broad band with a maximum at frequencies of ~ 63 ÷ 67 cm -1 (boson peak - BP). Such a case is absent in the respective crystals. The observed features are associated with relaxation and excess density of states of acoustic vibrations in irregularities is localized with nanometer-size of material. It is shown that the contribution of the different types of scattering in a low-frequency range depends on the degree of disorder in the material, which varies with the change of chemical composition and by doping. Keywords: glass, amorphous, chalcogenide. 1. INTRODUCTION Glass-like and amorphous semiconductors contain nanometer-size inhomogeneities, in which there is a certain order in the arrangement of structural elements. These in-homogeneities are not isolated entities, but are fragments of which are built entirely amorphous and glassy matters, i.e. they may be considered analogous to the crystal unit cell [1]. Information about these fragments give experiments on neutron diffraction [2] or X-rays [3], as well as the observable features in low-frequencies in the Raman scattering (RS) of such materials [4-7]. Raman spectra of amorphous and glassy materials differs from that of the corresponding crystals so that they plot in the low frequency ( & ’ 100 cm