Improving the performance of Ge2Sb2Te5 materials via nickel doping: Towards RF-compatible phase-change devices

Abstract

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 in amorphous and crystalline states were obtained using ellipsometry which echoes the results of X-ray diffraction. The material's thermal transport properties are measured using time-domain thermoreflectance, showing no change upon doping. The advantages of this doping system will open up opportunities for designing electrically reconfigurable high speed optical elements in the near-infrared spectrum.