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 a: P" with n as high as 7 has been found, indicating a multistep-multiphoton ex­citation process. To confi.rm 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 (u). For the slowest level u= 3 X 10- 18 cm2 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.