Phase purity and the thermoelectric properties of Ge2Sb2Te5 films down to 25 nm thickness

Thermoelectric phenomena strongly influence the behavior of chalcogenide materials in nanoelectronic devices including phase-change memory cells. This work uses a novel silicon-on-insulator experimental structure to measure the phase and temperature-dependent Seebeck and Thomson coefficients of Ge2Sb2Te5 films including the first data for films of thickness down to 25 nm. The Ge2Sb2Te5 films annealed at different temperatures contain varying fractions of the amorphous and crystalline phases which strongly influence the thermoelectric properties. The Seebeck coefficient reduces from 371 μV/K to 206 μV/K as the crystalline fraction increases by a factor of four as quantified using x-ray diffraction. The data are consistent with modeling based on effective medium theory and suggest that careful consideration of phase purity is needed to account for thermoelectric transport in phase change memory.