Effect of dopants on the structure and properties of Ge₂Sb₂Te₅ studied by Ab initio calculations

Ge₂Sb₂Te₅ is technologically important for phase-change random access memory applications. In this work, the effect of doping Ag, Cd, In and Sn on the structure and chemical bonding of Ge₂Sb₂Te₅ has been studied by ab initio calculations. It has been shown that the 3.7 at.% dopants drastically weaken the Te-Te bond strength in the-Te-(vacancy)-Te-configuration while maintaining its rocksalt symmetry. According to the analysis of formation energy, doping at the Ge site of Ge₂Sb₂Te₅ phase is more favourable. The doped Ge₂Sb₂Te₅ phases demonstrate either semiconductor or metallic behavior, which is attributed to the valence electrons of the dopants that mainly contribute to either the conductivity or chemical bonding.