Electrical switching and optical studies on amorphous GexSe35−xTe65 thin films

The electrical switching behavior of amorphous GexSe35−xTe65 thin film samples has been studied in sandwich geometry of electrodes. It is found that these samples exhibit memory switching behavior, which is similar to that of bulk Ge–Se–Te glasses. As expected, the switching voltages of GexSe35−xTe65 thin film samples are lower compared to those of bulk samples. In both thin film amorphous and bulk glassy samples, the switching voltages are found to increase with the increase in Ge concentration, which is consistent with the increase in network connectivity with the addition of higher coordinated Ge atoms. A sharp increase is seen in the composition dependence of the switching fields of amorphous GexSe35−xTe65 films above x = 21, which can be associated with the stiffness transition. Further, the optical band gap of a-GexSe35−xTe65 thin film samples, calculated from the absorption spectra, is found to show an increasing trend with the increase in Ge concentration, which is consistent with the variation of switching fields with composition. The increase in structural cross-linking with progressive addition of 4-fold coordinated Ge atoms is one of the main reasons for the observed increase in switching fields as well as band gaps of GexSe35−xTe65 samples.