Influence of light intensity on the photoluminescence of silicon nanostructures

The strong visible photoluminescence (PL) of nanostructured silicon, such as porous Silicon and silicon nanocrystals, is studied as a function of the power and the wavelength of the excitation laser source. The position of the PL peak is a function of the fluence: when the incident fluence is increased, the PL peak is blueshifted, and it is redshifted to its initial position when the fluence is decreased back. The PL yield is strongly attenuated with the increasing fluence and this decrease is partially irreversible. The behavior is also found to be a function of the wavelength of excitation: the shorter the excitation wavelength, the stronger the fluence effect. The PL temporal behavior has also been studied and appears to be weakly sensitive to the fluence. Fluence effects are compared to temperature effects and both are noticeably different, proving the absence of heating effects in our experiment for a wide range of incident power. Auger effect and state filling are discussed in order to understand the experimental results in the framework of the quantum confinement process. (C) 2002 American Institute of Physics.