Achievement

To learn about the phase transformation behavior of alloy nanocrystals, trainee Swanee Shin synthesized GeSn crystals by co-implantation of Ge and Sn into a silica matrix, yielding nanocrystals about 20 nm in diameter. He characterized their crystallinity and stress state using Raman spectroscopy and their structure and composition using STEM and XEDS analysis. We learned how to amorphize and homogenize GeSn nanocrystals using a single pulse excimer laser. Rapid thermal annealing led to recrystallization and segregation of Ge and Sn. This resulted in an ongoing investigation of the phase change temperature dependence of the Ge:Sn alloy system. We focus on fundamental science (phase transformations), but the potential applications of Ge1-xSnx alloys have been intensively studied as a promising material for light emitting devices due to the reported indirect to direct bandgap transition at x~0.1, and at the nanoscale, GeSn quantum dots show the size-dependent quantum confinement effect.