VARIATION OF DOUBLE-PEAK STRUCTURE IN PHOTOLUMINESCENCE SPECTRA FROM POROUS SILICON WITH EXCITATION WAVELENGTH

We have systematically observed at room temperature the variations of photoluminescence(PL) from porous silicon(PS) with excitation wavelength in a range from 260 to 460nm al 20nm intervals. In the range from 260 to 320nm, the PL spectra for one of the two studied samples show clear double-peak structure. Each spectrum can be fitted by two Gaussian functions with their peaks centered at about 610nm and 710nm, respectively. The peak position and the full width at half maximum of the two Gaussian functions change little with excitation wavelength. The above phenomena seem hard to interpret using the quantum confinement model, but can be understood in the quantum confinement / luminescence centers model (G.G.Qin and Y.Q.Jia, Solid State Commun. 86, 559(1993)), ii we suppose that there are two kinds of luminescence centers adsorbed on the surfaces of nano-scale silicon (NS) units or situated in the SiOx layers covering the NS units in PS.