Oxide-free blue photoluminescence from photochemically etched porous silicon

It has been shown that the blue photoluminescence (PL) of porous silicon (PS) can be obtained simply from postanodization illumination by white light without any oxidation processes. The PS samples were formed on 5-6 Ohm cm p-type (100) Si wafers. The anodization was carried out in an ethanoic HF solution at a current density of 50 mA/cm(2) for 5 min in the dark. After the anodization, the samples were illuminated under the open-circuit condition by a 500 W tungsten lamp for several minutes. The PL measurements of prepared PS samples were carried out in vacuum. With increasing the postanodization illumination time, the PL band exhibited a continuous shift from red to blue. During this blue shift, fourier transform infrared spectra did not show any signs of the growth of the surface oxide. In addition, the emission energy dependence of the PL decay time for each PL band behaved in accordance with a universal curve. These results strongly suggest that there is an oxide-free mechanism in the PL emission from PS throughout the visible range. (C) 1996 American Institute of Physics.