XEOL STUDIES OF POROUS SILICON

Oxidised porous silicon emits luminescence in two distinct bands in th e visible region. The fast blue (tau similar to ns) and slow red (tau similar to mu s at 300K) bands are studied via the separate methods of time-resolved XEOL in single-bunch mode and wavelength-selective and total XEOL in multi-bunch mode. Measurements have been conducted at th e silicon K-edge (1840eV) and L-2,L-3-edge for freshly prepared and ox idised porous silicon and related samples. Both methods give conclusiv e evidence that the fast, blue luminescent site is defects in silica o r suboxide formed near to the Si/SiO2 interface, whereas the slower, r ed band originates from smaller silicon particles of diameter 14 Angst rom or less found in porous silicon. The XEOL process is discussed and range estimates of the spatial. separation between the photoionisatio n event and radiative recombination are made.