Effect of some metallic impurities on the density of localized states in a-Se80Te20 thin films

The present paper reports the d.c. conductivity measurements at high electric fields in vacuum-evaporated thin films of amorphous Se80Te20, Se75Te20Ge5 and Se75Te20Sb5 systems. Current-voltage (I-P) characteristics have been measured at various fixed temperatures. In all the samples, at low electric fields ohmic behavior is observed. However, at high electric fields (E similar to 10(4) V/cm), non-ohmic behavior is observed. An analysis of the experimental data confirms the presence of space charge limited conduction (SCLC) in all the glassy materials studied in the present case. From the fitting of the data to the theory of SCLC, the density of defect states (DOS) near Fermi level is calculated. The role of the aforesaid impurities in a-Se80Te20 is found to be entirely different. In case of Sb, an increase in DOS is observed. However, a decrease is observed in case of Ge. The change in DOS on impurity incorporation is explained in terms of the change in structure of these glasses. (C) 2004 Elsevier Ltd. All rights reserved.