Electronic structure and optical properties of silicon nanowires: A study using x-ray excited optical luminescence and x-ray emission spectroscopy

Abstract

We report a soft x-ray excited optical luminescence (XEOL) and x-ray emission spectroscopy (XES) study of silicon nanowires (SiNW) with excitations at the silicon $K$ and ${L}_{3,2}$ edge, respectively. It is found that the XEOL of SiNW exhibits several luminescence bands at $\ensuremath{\sim}460$, $\ensuremath{\sim}530$, and $\ensuremath{\sim}630\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. These luminescence bands are broad and are sensitive to the $\mathrm{Si}\phantom{\rule{0.2em}{0ex}}1s$ excitation channel (Si versus $\mathrm{Si}{\mathrm{O}}_{2}$ whiteline). These chemical- and morphology-dependent luminescences are attributable to the emission from the encapsulating silicon oxide, the quantum-confined silicon crystallites of various sizes embedded in the oxide layer, and the silicon-silicon oxide interface. XES clearly shows the presence of a relatively thick oxide layer encapsulating the silicon nanowire and the densities of states tailing across the Fermi level. The implications of these findings to the electronic and optical properties of silicon nanowires are discussed.