Crystallization of Nanometer Ge2Sb2Te5 Amorphous Regions Embedded in the Hexagonal Close Packed Structure

As an aid toward a better understanding of data retention of phase change memories we have analyzed in situ by Transmission Electron Microscopy the crystallization of amorphous Ge2Sb2Te5 dots of 100 nm and 20 nm diameter, embedded in the hexagonal crystalline phase. Amorphization was obtained by 40 keV Ge+ irradiation at LN2 through Electron Beam Lithography masked pattern. At 75 degrees C/90 degrees C, crystallization in 100 nm dots occurs by grain growth from the surrounding crystalline material, with an initial growth velocity of 0.6 (6.4) pm/s followed by a slower rate of 0.14 (1.7) pm/s. At 75 degrees C, the 20 nm amorphous regions disappear just after two hours of annealing.