Photoluminescence in silicon powder grown by plasma-enhanced chemical-vapor deposition: Evidence of a multistep-multiphoton excitation process.

Abstract

The dynamics of the infrared photoluminescence (PL) in silicon powder grown by plasma-enhanced chemical-vapor deposition (PECVD) of silane is reported. A nonlinear dependence of PL intensity on laser power of the form I\ensuremath{\propto}${\mathit{P}}^{\mathit{n}}$ with n as high as 7 has been found, indicating a multistep-multiphoton excitation process. To confirm this hypothesis a very detailed theoretical and experimental analysis has been performed. As a result, the lifetimes of several levels in the excitation chain have been determined, as well as the optical cross section (\ensuremath{\sigma}). For the slowest level \ensuremath{\sigma}=3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}18}$ ${\mathrm{cm}}^{2}$ and the lifetime is as long as 400 ms. As the energy of the emitted photon is smaller than that of the excitation photon, a model involving a considerable nonradiative energy relaxation, together with a tunnel effect is proposed.