Influence of Sn doping upon the phase change characteristics of Ge2Sb2Te5

The influence of Sn doping upon the phase change characteristics of Ge2Sb2Te5 alloys has been investigated using four-point-probe electrical resistance measurements, grazing incidence X-ray diffraction (XRD), X-ray reflectometry (XRR) and variable incident angle spectroscopic ellipsometry (VASE), a static tester and atomic force microscopy (AFM). For a Ge2Sb2Te5 alloy doped with 4% Sn, two transition temperatures are observed in the temperature dependent sheet resistance measurements at 125 C and 250 C, respectively. The evolution of structures upon annealing, investigated by XRD, reveals that the first transition is caused by the crystallization of the amorphous film to a NaCl-type structure, while the second transition is related to the transition to a hexagonal structure. The density values of 6.02±0.05 g cm-3, 6.38±0.05 g cm-3 and 6.42±0.05 g cm-3 are measured by XRR for the film in the amorphous, NaCl-type and hexagonal structure, respectively. Ultra-fast crystallization, which is correlated with a single NaCl-structure phase and the reduced activation barrier, is demonstrated. Sufficient optical contrast is exhibited and can be correlated with the density change upon crystallization. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)