Insulator-metal transition in GeTe/Sb2Te3 multilayer induced by grain growth and interface barrier

Unlike its two components, the temperature coefficient of resistivity (TCR) of GeTe/Sb2Te3 multilayer (ML) increases from negative to positive on annealing, indicating an insulator-metal transition (IMT). Impedance spectroscopy measurements demonstrate that the grain boundary resistance (negative TCR) determines the total resistance of initial ML. As grain grows, which is confirmed by x-ray diffraction, scanning electron microscope, and optical reflectivity measurements, the contribution of grain resistance (positive TCR) increases gradually to the leading part and finally accomplishes the IMT in a sufficiently crystallized film. Furthermore, the artificially introduced interfaces form additional potential barrier in ML and also modulate its IMT behavior. (C) 2011 American Institute of Physics. [doi:10.1063/1.3664132]