Origin of carrier-type reversal in Pb-Ge-Se glasses: a detailed thermal, electrical, and structural study

Abstract

A long-standing and important problem in glass science has been carrier-type reversal (CTR) in semiconducting glasses. This phenomenon is exhibited by Pb-Ge-Se glasses also. It has been addressed here by carrying out detailed electrical, thermal, and spectroscopic investigations. Pb_xGe_42-xSe₅₈ (x = 0-20) glasses were prepared by a two stage melt-quenching process and characterized using x-ray diffraction, high-resolution electron microscropy, and energy dispersive analysis of x-rays. Thermoelectric power and high-pressure electrical resistivity have been measured. IR, Raman, and X-ray adsorption near edge structure spectroscopies have been used for examining the glass structures as well as differential scanning calorimetry (DSC) for studying the thermal properties. A structural model based on the chemical nature of the constituents has been proposed to account for the observed properties of these glasses. Effect of Pb incorporation on local structures and qualitative consequences on the energy band structures of Ge-Se glasses has been considered. The p → n transition has been attributed to the energetic disposition of the sp3d2 band of Pb atoms, which is located closely above the lone pair band of selenium. This feature makes Pb unique in the context of p → n transition of chalcogenide glasses. The model can be extended successfully to account for the CTR behavior observed in Bi containing chalcogenide glasses also.