Segregation-induced Ge precipitation in Ge2Sb2Te5 and N-doped Ge2Sb2Te5 line cells

Electromigration in Ge2Sb2Te5 and N-doped Ge2Sb2Te5 line cell structures has been studied by mapping out electric field/current-induced composition changes using x-ray energy dispersive spectroscopy. Both materials exhibit pronounced segregation in a molten state, with Te moving toward the anode and Ge and Sb toward the cathode. The width of the transition region from a composition of over 90% Te to over 90% Ge–Sb was 500 nm for an electric field of 1.1 × 107 V/m. In the Ge–Sb-rich end of the cell, Ge precipitates out of the melt, forming almost pure Ge inclusions with a size up to 100 nm. The Ge–Sb–Te segregation and precipitation do not appear to be affected by doping with nitrogen.