Influence of local structure and network connectivity on the electrical switching of some Te-based chalcogenide glasses

Abstract

Chalcogenide glass (ChG) materials have gained wide attention because of their applications in phase change non-volatile memories (PC-RAM), optical rewritable disks (CD-RW and DVD-RW), infrared detection and thermal imaging. One of the significant properties of ChG materials is the change in the resistivity of the material when a metal such as Al, Cu, and Sb are added. Electrical switching is another interesting and important property possessed by several Te based chalcogenides. Switching is the rapid transition between a high resistive OFF state to low resistive ON state driven by an external electric field and characterized by a threshold voltage. The contrast in electrical resistivity between the OFF and ON state is > 103 Ohms. This electrical switching can be of two types: (i) Threshold switching and (ii) memory switching. Upon the removal of the applied field threshold switching device reverts back to the OFF state, whereas the memory device retains the ON state. Memory switching, a non-reversible transition is understood based on the thermal mechanism where the applied electric field drives the system from amorphous/glass (OFF) to crystalline (ON) state. Threshold switching, a reversible transition is understood based on electronic transitions. Electrical switching is mainly influence by the network connectivity, rigidity, local structure, and glass forming ability. Investigations on electrical switching in chalcogenide glasses help in understanding the mechanism of switching which is necessary to select and modify materials for specific switching applications. In this work, we have studied the influence of network connectivity,local structure and glass forming ability on electrical switching in melt quenched bulk Al-Te, Al-Te-Sb, Al-As-Te and GeTe4-As2Se3 chalcogenide glasses. Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), Raman Spectroscopy, Magic Angle Nuclear Magnetic Resonance (MAS-NMR), Nano-Indentation methods were used to study the properties of these glasses. From the obtained results the threshold and memory switching exhibited by these glasses were understood uniquely by the thermal mechanism.