Alternative electronic density of states model for metastable crystalline phase of Ge₂Sb₂Te₅

Motivated by future data storage requirements, Ge2Sb2Te5 is studied for application in phase-change random access memory. The currently accepted density of states (DOS) models for the cubic crystalline phase, based on first-principles calculations, are reviewed. An alternative DOS model, which incorporates band tails and an antimony vacancy multivalent defect, is proposed. Solar cell capacitance simulation results reveal that the alternative model is successful in predicting a free hole concentration and Fermi level position consistent with previous Hall effect and thermopower measurements respectively. The conduction band tail, which has not previously been incorporated within the DOS model of the crystalline phase, is shown to contribute to this success.