Electrical switching in germanium telluride glasses doped with Cu and Ag

Electrical switching in germanium telluride glasses containing metallic atoms (Cu and Ag) has been investigated. All these glasses are found to exhibit memory switching. The switching fields of these glasses are compared with the thermal parameters evaluated from DSC studies and the results are explained on the basis of the thermal model. The composition dependence of the switching field and the thermal parameters show interesting variations at the critical compositions which correspond to the rigidity percolation and the chemical thresholds of these glasses. Chalcogenide glasses subjected to high electric fields often exhibit non-linear I–V characteristics. When the applied field attains a critical value, an unstable situation arises leading to a switching from a low-conducting state (OFF) to a high-conducting state (ON). This electrical switching is of two types, namely memory switching and threshold switching [1–3]. If the ON state observed in these materials is retained even after the applied field is reduced to zero, it is called a memory switching. Instead, if the material retraces its path to the original OFF state when the applied field is reduced to zero it is called a threshold switching. Threshold switching materials require a holding current and voltage to sustain the ON state. Once the holding current is removed, they revert back to their original OFF state. Thermally induced transitions (thermal mechanism) under high field explain the memory switching whereas the response of electrons to the applied high field (electronic mechanism) is used to explain the threshold switching [4–10]. The thermally induced transitions in a chalcogenide glass are amorphization, crystallization, and melting. The applied electric field accelerates the electrons and they emit phonons. This increases the temperature of the material due to Joule heating and the material crystallizes in between the electrodes [4, 8, 11]. Here the important point is ∗ Corresponding author how the resultant crystalline state occurs: by glass→crystal or glass→melt→crystal transformation. However, earlier microradiometer measurements give evidence for the later process [11–15]. Hence, the formation of a crystalline filament between the electrodes is important to observe memory switching in chalcogenide glasses. In turn, crystallization of these glasses depends on the properties of the material such as thermal diffusivity, network rigidity, chemical ordering, etc. The metallic impurities such as copper and silver added to chalcogenide materials bring interesting variations in their properties. They enter the structural network of chalcogenide glasses in a special way and increase the network connectivity, crystallizing ability, and the electrical conductivity [16, 17]. In this work, I–V characteristics of Ge-Te glasses containing Cu and Ag have been studied. Differential scanning calorimetric (DSC) studies also conducted on these glasses to understand the thermally induced phase transitions. The general thermal model provides an understanding of the memory switching observed in these bulk glasses.