Photo-oxidation effects of light-emitting porous Si

The effects of light illumination on porous silicon (PSi) properties have been studied using photoluminescence (PL), PL excitation (PLE), and x-ray photoelectron spectroscopy (XPS) measurements. The PL spectrum evolution in PSi sample under light illumination at various wavelengths indicates that the photo-oxidation occurs and causes a decrease in its intensity with increasing illumination time t. The decrease in the PL intensity IPL can be written as logarithmic expression, namely, the Elovich equation I-PL alpha-alpha 1n t, where alpha is the quenching rate of the PL intensity associated with the native oxide growth. The alpha value is dependent on the illuminated photon energy E-po in a manner alpha=0.050E(po). Each PL spectrum can be deconvoluted into four Gaussian peaks. The higher the PL peak energy, the larger its photo-oxidation-induced blueshift. This fact and XPS results support that the light emission in a porous sample is due to the quantum-size effect, i.e., relaxation of the momentum conservation at and above the indirect absorption edge (supra-indirect-gap emission). The PLE spectra suggest that the surface hydrogen termination should influence the highly excited carrier dynamics in nanocrystalline PSi materials. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3140677]