Multilevel modeling for charge transport in Ovonic chalcogenide materials and devices

A sound physical model for electric conduction in Ovonic materials is presented. Trap-limited conduction is assumed to determine the part of the I (V) curve below the characteristic threshold of these materials. Band transport comes into play at and above threshold, where the cooperative electron-electron interactions couple the conduction band with the traps. The model can be implemented into numerical simulations at different levels, ranging from the description of nanometric systems of simple geometry to device simulation of complex structures based on chalcogenide glasses used for phase-change memories. Simulations incorporating Poisson self-consistency provide information about the electric field, carrier concentration, and electron temperature along the device, giving a clear physical picture of the Ovonic process. Device-simulation models provide a compact and flexible formalism suitable for tailoring technologically-relevant features like, e.g., the threshold voltage, the effect of external contacts, and the electric field inside the device. The results of the multilevel simulations account for and interpret the main experimental findings in phase-change memory cells.