Visible Photoluminescence from Anodically Oxidized Porous Silicon

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Abstract
Porous silicon (PS) anodically oxidized just after anodization of a silicon wafer has been investigated. Room-temperature photoluminescence (PL) peaks shifted to shorter wavelengths at the initial oxidation stage, followed by the PL blue shift saturation upon further oxidation. The temperature coefficient of the PL peak energy was -0.2 meV/K in the former while it was -0.5 meV/K in the latter. PL excitation spectra around 4 eV also showed changes corresponding to the PL blue shifts with oxidation. The PL mechanism is discussed in relation to band-gap widening due to the size reduction effect and appearance of luminescence centers.