Relationship between statistical shift of the Fermi level and activation energy of conductivity in phase-change materials

The non-Arrhenius behaviour of conductivity of phase-change materials is analysed in terms of the statistical shift of Fermi level. To show this connection, a simplified model for the density of states in a phase-change material is proposed to simulate the temperature dependence of the Fermi level. Comparison of the temperature dependence of conductivity of Ge 2 Sb 2 Te 5 with the simulation results allowed estimating the position of defect levels in the bandgap.