Photoluminescence fromSi1−xGexalloy nanocrystals

Abstract

Photoluminescence (PL) from ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ alloy nanocrystals $(\mathrm{nc}\ensuremath{-}{\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x})$ as small as 4\char21{}5 nm in diameter was studied as a function of the Ge content. The $\mathrm{nc}\ensuremath{-}{\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ samples were fabricated by the cosputtering of Si, Ge, and ${\mathrm{SiO}}_{2}$ and postannealing at $1100\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ High-resolution transmission electron microscopy, electron diffraction, and Raman spectroscopy clearly showed the growth of spherical ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ nanocrystals in ${\mathrm{SiO}}_{2}$ matrices. The PL spectra of $\mathrm{nc}\ensuremath{-}{\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ were found to be very sensitive to the Ge content. A low-energy shift of the PL peak from the widened band gap of Si nanocrystals to that of Ge nanocrystals with increasing Ge content was clearly observed.