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The crystallization behavior of nitrogen-doped amorphous Ge 2 Sb 2 Te 5 -(N) phase-change thin films was studied by utilizing differential scanning calorimetry, in situ ellipsometry and in situ transmission electron microscopy. The combined analysis of in situ ellipsometry isotherms of amorphous Ge 2 Sb 2 Te 5 -(N) films and the Johnson-Mehl-Avrami equation revealed that the crystallization process of amorphous Ge 2 Sb 2 Te 5 -(N) films changes depending on the nitrogen content. The crystallization behavior of Ge 2 Sb 2 Te 5 film revealed a two-step process that includes spherical-nucleation and disc-shaped grain growth. In contrast, nitrogen-doping into Ge 2 Sb 2 Te 5 thin films suppresses the second step and the crystallization of Ge 2 Sb 2 Te 5 -(N) becomes a one-step process that is the primary nucleation process. The number of nucleation sites during the crystallization of amorphous Ge 2 Sb 2 Te 5 -(N) films, increased markedly with the annealing temperature in the spherically shaped nuclei and eventually saturated. The effective crystallinity of Ge 2 Sb 2 Te 5 -(N) alloy films decreased with the increase in nitrogen content, mainly due to the grain-size refinement.
Seo et al. (2000) studied this question.