Microstructure and optical properties of phase-change Ge-Sb-Te nanoparticles grown by pulsed-laser ablation

Phase-change Ge-Sb-Te (GST) nanoparticles have been in-situ synthesized by a pulsed-laser ablation method. During the ablation process, growth parameters including temperature of heat treatment, pressure, and laser fluence are extensively explored. Scanning and transmission electron microscopy are used to study microstructure and phase formation of the nanoparticles. Fourier transform analysis of electron micrographs exhibits an evidence of existence of the stoichiometric single GST-225 phase. We have measured micro-Raman scattering spectra of commercially available GST-124, -147, and -225 bulk and GST nanoparticles. Lack of the amorphous Te-Te stretching mode near 150 cm^-1 from the Raman spectra of the bulk samples indicates that the samples are well-crystallized. From the measurements of GST nanoparticles with different growth conditions, we could get information towards the optimal growth conditions for better crystalline quality of the GST nanoparticles. Our results suggest that micro-Raman scattering spectroscopy can be used to study phases and phase changes in the GST bulk crystals and nanoparticles through local structural information, which is being developed for low-power non-volatile memory applications.