Optical properties and quantum confinement in ultrafine single crystal silicon nanowires synthesized by thermal evaporation without catalyst

Ultrafine single crystal silicon nanowires (SiNWs) were grown along the < 110 > direction by thermal evaporation without catalyst, and were studied by electron microscopy and optical spectroscopy. Simulation of the first-order Raman scattering spectrum of the wires indicates that the Raman shift and asymmetric broadening line shape are due to phonon confinement and a narrow diameter distribution of the SiNWs, and confirms that the mean diameter of the wires is 2 nm, which is smaller than the excitonic Bohr radius of Si. Further analysis shows that the unique intense purple photoluminescence (PL) peak and blue-shift of absorption spectrum of the wires result both from the increase of the energy band gap due to quantum confinement of the carriers, and from the confinement of excitons in the ultrafine SiNWs, suggesting potential applications of the wires in optical and optoelectronic nanoscale devices.