Controlled growth of SiNPs by plasma synthesis

Quantum confined silicon nanoparticles (SiNPs) may allow for the fabrication of an all silicon multiple junction photovoltaic cell, or novel photovoltaic cells that surpasses the single junction limitations. One method of growing SiNPs is by PECVD where the plasma is confined to a quartz tube. To further understand this technique, computational fluid dynamic calculation were coupled with experimental growths, which allows for the development of a phase diagram based around the reactor pressure, and gas flow. SiNP size and crystallinity were evaluated using a combination of Raman scattering, X-ray diffraction, and transmission electron microscopy (TEM), these results were used to further the develop the phase diagram. For residence times less than 1 ms, SiNPs were produced a band gap of >1.6 eV, but very low crystallinity. By maintaining a constant low gas flow (100 sccm) and increasing reactor pressure, crystallinity and size of the SiNPs were improved and increased, respectively. For SiNPs grown with a constant residence time (~2 ms), we observe a reduction in the crystallinity with increased gas flow. Closer inspection by TEM showed a significant amount of a-Si with the SiNPs. Using this growth technique we can reliably grow SiNPs with diameters from 3 nm to 8 nm, relating to a photoluminescence peak position from 1.6 eV to 1.3 eV. This range is ideal for the development of an all silicon tandem photovoltaic cell.