Influence of doping upon the phase change characteristics of Ge2Sb2Te5

Abstract

The influence of doping upon the phase change characteristics of Ge2Sb2Te5 (GST) has been determined with a variety of techniques including four-point-probe electrical resistance measurements, grazing incidence X-ray diffraction (XRD), X-ray reflectometry (XRR) and a variable incident angle spectroscopic ellipsometer (VASE) and a static tester. Doping with Bi, Sn or In maintains the NaCl-type crystalline structure of GST but expands the lattice due to the larger atomic radii. Sufficient optical contrast is exhibited and can be presumably correlated with the pronounced density change upon crystallization. In the Bi and Sn doped case transition temperatures are reduced with regard to the undoped case. Ultra-fast crystallization within 10 ns is demonstrated, which is correlated with a single NaCl-structure phase and a lower transition temperature arising from the weaker bonds. In the In doped case, however, crystallization is retarded, which can be correlated with the observed phase separation and the increased transition temperature.