Investigation of crystallization behavior of sputter-deposited nitrogen-doped amorphous Ge2Sb2Te5 thin films

The crystallization behavior of nitrogen-doped amorphous Ge2Sb2Te5-(N) phas e-change thin films was studied by utilizing differential scanning calorime try, in situ ellipsometry and in situ transmission electron microscopy. The combined analysis of in situ ellipsometry isotherms of amorphous Ge2Sb2Te5 -(N) films and the Johnson-Mehl-Avrami equation revealed that the crystalli zation process of amorphous Ge2Sb2Te5-(N) films changes depending on the ni trogen content. The crystallization behavior of Ge2Sb2Te5 film revealed a t wo-step process that includes spherical-nucleation and disc-shaped grain gr owth. In contrast, nitrogen-doping into Ge2Sb2Te5 thin films suppresses the second step and the crystallization of Ge2Sb2Te5-(N) becomes a onestep pro cess that is the primary nucleation process. The number of nucleation sites during the crystallization of amorphous Ge2Sb2Te5-(N) films, increased mar kedly with the annealing temperature in the spherically shaped nuclei and e ventually saturated. The effective crystallinity of Ge2Sb2Te5-(N) alloy fil ms decreased with the increase in nitrogen content, mainly due to the grain -size refinement.