Sintering Plasma-Synthesized Silicon Germanium Nanocrystals

Abstract

Alloyed silicon germanium has been used for its thermoelectric properties for over 40 years. The dimensionless thermoelectric figure of merit is proportional to a material’s electrical conductivity and Seebeck coefficient squared and inversely proportional to the thermal conductivity. The figure of merit can be increased by nanostructuring silicon germanium, reducing lattice thermal conductivity. Plasma-synthesized silicon germanium nanocrystals offer potential to meet this need while also being able to fine tune the material’s properties through doping, altering the silicon germanium ratio, and changing the nanoparticle size. Intrinsic, boron-doped, and phosphorous-doped silicon germanium films and powders were synthesized in a capacitively coupled radio frequency plasma. They were characterized to determine composition and crystallinity. As synthesized, samples are extremely electrically insulating. In order to increase electrical conductivity, several post-treatment processes were investigated to sinter the nanoparticles including rapid thermal annealing, hot pressing, laser sintering, and intense pulsed light sintering.