Electronic and atomic structure of Ge2Sb2Te5 phase change memory material

Electronic structure calculations are presented for various model structures of the crystalline and amorphous phases of Ge2Sb2Te5. The structures are all found to possess a band gap of order 0.5 eV, indicating closed shell behaviour. It is pointed out that structural vacancies in A7-like Ge2Sb2Te5 are not electronically active. In addition, A7-like structures do not support valence alternation pair defects, which are one model of the conduction processes in the amorphous phase in non-volatile memories.