Structural and transport properties of amorphous Se-Sb-Ag chalcogenide alloys and thin films

Bulk Se80-xSb20Agx (8 <= x <= 14) chalcogenide glasses have been prepared by conventional melt quenching technique. Thin films of the above composition have been prepared by thermal evaporation of the bulk material. X-ray diffraction studies have been performed to investigate the structure of the thin films. The presence of only broad features and the absence of any sharp peaks in the X-ray diffractogram confirm that the films are amorphous in nature. The addition of Ag to the Se-Sb host has been found to segregate as Ag2Se nanophase. Scanning electron microscopy images show that both the Ag-rich and Sb-rich nanophases co-exist in this system. The glass transition temperature and the crystallization temperature of the bulk samples have been determined by Differential Scanning Calorimetric analysis performed under non-isothermal conditions. The dark electrical conductivity of the Se80-xSb20Agx (8 <= x <= 14) thin films has been measured as a function of temperature and has been found to increase with increase in temperature as well as with increase in Ag content. It has been found to be activated over the entire temperature range (273-333 K). The activation energy for electrical conduction and the optical bandgap are found to decrease with increase in Ag content and follow the same trend. It has been observed that the electrical activation energy is nearly half of the optical bandgap indicating that there are trap states in the gap that pins the Fermi level. (C) 2007 Elsevier B.V. All rights reserved.