Synthesis and Characterisation of In Situ Doped Silicon Nanoparticles

In situ boron, or phosphorous doped silicon nanoparticles were synthesised by pyrolysis of monosilane-diborane and monosilane-phosphane mixtures in free-space reactors. The studies were performed under atmospheric pressure in a laboratory reactor and a pilot plant for examination of scale-up effects. In the laboratory scale experiments, 1 vol % monosilane diluted in helium was used. The synthesis temperature varied between 600 and 800(degrees)C. Pilot plant tests were run at 600 degrees C with 13.3 vol % silane diluted in hydrogen. The dopant content of the synthesised silicon powders was characterised by ETV-ICP-OES. Further investigations were carried out by using SEM, XRD, particle size analysis and FT-IR. An inhibition of the boron incorporation into the growing silicon lattice was found during the decomposition of the silane-diborane mixtures. This effect is a result of the low thermal stability of diborane. Silicon powders with higher boron contents and a wider particle size distribution leading to bigger particles, which showed no affinity to electrostatic charging, were obtained on the pilot plant scale. In phosphorus doping, reactor temperature was found crucial for the doping process.