  High-speed electrical switching of Ge2Sb2Te5 (GST) remains a challenging task
due to the large impedance mismatch between the low-conductivity amorphous
state and the high-conductivity crystalline state. In this letter, we
demonstrate an effective doping scheme using nickel to reduce the resistivity
contrast between the amorphous and crystalline states by nearly three orders of
magnitude. Most importantly, our results show that doping produces the desired
electrical performance without adversely affecting the film's optical
properties. The nickel doping level is approximately 2% and the lattice
structure remains nearly unchanged when compared with undoped-GST. The
refractive indices at amorphous and crystalline states were obtained using
ellipsometry which echoes the results from XRD. The material's thermal
transport properties are measured using time-domain thermoreflectance (TDTR),
showing no change upon doping. The advantages of this doping system will open
up new opportunities for designing electrically reconfigurable high speed
optical elements in the near-infrared spectrum.
