Effect of Annealing Temperature on the Microstructure and Resistivity of Ge₂Sb₂Te₅ Films

The effect of annealing temperature on crystallization of amorphous Ge₂Sb₂Te₅ films with thickness of 40 nm is studied by TEM and AFM methods. The relationship between microstructure and resistivity of the Ge₂Sb₂Te₅ film is investigated. From the TEM measurements, the grain size of crystallites increases gradually as the annealing temperature increases. When the annealing temperature is too high, voids are formed, which may originate from evaporation of the Ge₂Sb₂Te₅ film at the elevated temperatures, formation of sink, being nucleated by residual vacancies, and surface roughness. The resistivity of the Ge₂Sb₂Te₅ film decreases with the increasing annealing temperature and has slight changes when the temperature is higher than 400°C. Phase transitions and scattering of crystallite boundaries may be the major factors affecting the resistivity of the Ge₂Sb₂Te₅ film.