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

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∝${\mathit{P}}^{\mathit{n}}$ 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 (σ). For the slowest level σ=3×${10}^{\mathrm{-}18}$ ${\mathrm{cm}}^2$ 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.