Athermal amorphization of crystallized chalcogenide glasses and phase-change alloys

Chalcogenide alloys can exist in both crystalline and amorphous phases, with light-induced changes between the two states. While it is generally believed that in the amorphization process light predominantly serves to melt the material that is subsequently quenched into the amorphous phase, there has been accumulating evidence, both experimental and theoretical, that photoamorphization can be athermal. In this review, we present experimental and simulational results demonstrating that both chancogenide glasses, such as pure selenium and As₅₀ Se₅₀, and phase-change materials such as Ge₂ Sb₂ Te₅ can be rendered amorphous without going through a conventional molten phase. The ability of chalcogenides to be amorphized athermally is attributed to the presence in these materials of pronounced bonding energy hierarchy between the shorter and longer bonds. Chalcogenide glasses and phase-change alloys are characterised by pronounced bonding energy hierarchy between co-aligned shorter and longer (resonant) bonds. The existing experimental and simulational evidence suggests that it is this hierarchy that makes athermal amorphisation of these materials possible.