XEOL studies of porous silicon

Abstract

Oxidised porous silicon emits luminescence in two distinct bands in the 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 the silicon K-edge (1840eV) and L-2,L-3-edge for freshly prepared and oxidised porous silicon and related samples. Both methods give conclusive evidence that the fast, blue luminescent site is defects in silica or suboxide formed near to the Si/SiO2 interface, whereas the slower, red band originates from smaller silicon particles of diameter 14 Angstrom or less found in porous silicon. The XEOL process is discussed and range estimates of the spatial. separation between the photoionisation event and radiative recombination are made