Hexagonal ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$ crystals consist of symmetric building blocks, in which Ge and Sb atoms are randomly distributed in two kinds of atomic layers with different compositions. Their physical properties are strongly influenced by the chemical disorder arising from both Ge/Sb intermixing and deviations from the perfect stoichiometry, which are responsible for the high $p$-type doping observed experimentally. We present a systematic first-principles study of the effects of chemical disorder on the structural, electronic, and transport properties of doped ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$ crystals. Crystals with a Ge/Sb intermixing rate below 50% have a lower energy and are all expected to exist in the same samples, in accordance with experimental observations. The modification of their structural parameters, electronic band dispersion, and electronic conductivity is described as functions of the Ge/Sb intermixing rate and doping. In particular, we show that conductivity changes depend on a subtle balance between disorder-induced carrier scattering events and modifications of the carrier density, which themselves depend on Ge/Sb intermixing and on the nature and concentration of the point defects responsible for doping. Our results provide insight into the microscopic origins of the electronic properties of GeSbTe materials for phase change memories, whose microstructure contains hexagonal ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$ grains.

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• Doping effects
• Electrical conductivity
• Electronic structure
• Disordered systems
• Coherent potential approximation
• Density functional calculations
• Korringa-Kohn-Rostoker method