Electronic conduction in amorphous semiconductors and the physics of the switching phenomena

A three-fold classification of amorphous semiconductors into (i) elemental, (ii) covalent alloys, and (iii) ionic and tightly bound amorphous materials is proposed. The experimental evidence supporting a simple band model for the amorphous covalent alloys is presented. The present understanding of the reversible switching effects and of the switching with memory is discussed.