Electronic and Thermoelectric Properties of Layered Sn- and Pb-Doped Ge2Sb2Te5 Alloys Using First Principle Calculations

A computational study on stable hexagonal phase of undoped, and Sn- and Pb-doped Ge2Sb2Te5 (GST) phase change materials has been carried out. The electronic structure, lattice dynamics and thermoelectric properties of doped GST have been extensively investigated using ab initio methods with virtual crystal approximation. The hexagonal symmetry of the GST is maintained with the addition of Sn and Pb dopants. The lattice parameters and atomic volume of the Sn-doped GST structure is larger than that of the undoped GST. Electronic band structure calculations show that there is an increase in band gap with the increase in the concentration of Sn (a parts per thousand currency sign4.4 at.%). However, with the addition of a very small amount of Pb, there is a continuous decrease in lattice parameters and band gap values. The calculated energy band structure is then used in combination with the Boltzmann transport equation to calculate the thermoelectric parameters of GST and Sn- and Pb-doped materials. Seebeck coefficient (S), electronic thermal conductivity (kappa (e)) and the thermoelectric figure-of-merit (ZT) have been calculated with the help of BoltzTraP code. It was found that the thermoelectric properties of GST are enhanced with the addition of Sn.