Charge transport models for amorphous chalcogenides

The chapter addresses the issue of transport models applied to the amorphous chalcogenides which, in the last decades, have acquired importance in the design and manufacture of solid-state memories. After an introductory part where the main properties of the materials are outlined, ab initio atomistic, and semiclassical computational approaches for the study of the atomic structure and the features of electronic states of chalcogenides are briefly illustrated. This part is concluded by a description of the resistance-drift phenomenon and of how the simulation approaches contributed to the comprehension of the underlying physics. The successive section summarizes a variety of physical models and numerical methods useful for describing charge transport in the materials. The issue is developed in the two subsequent sections, dealing with microscopic and macroscopic models, respectively. The first section of the pair addresses the trap-limited transport model in the hydrodynamic form and discusses a 3D network of randomly placed traps. Specific issues, like detrapping due to electron-electron interaction and the probability of inter-trap transitions, are addressed here. Finally, ab initio quantum models for ultrascaled devices are illustrated.