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.