The correlation of dimensionality with emitted wavelength and ordering of freshly produced porous silicon

Freshly produced red, yellow and green emitting porous Si specimens have been studied by NEXAFS and EXAFS (near edge and extended x-ray absorption fine structure). The emission peaks are at 690, 580, and 520 nm, which almost covers the full visible range that direct anodization can achieve. The correlation between the co-ordination numbers of the first, second and third Si neighbor shells from Fourier transform fitting of EXAFS and both emission peak energies and optical band gaps estimated by PLE (photoluminescence excitation dependence) suggests that the nanostructures of the PS are nanowires, rather than nanocrystalline. Two types of quantum nanowire with one and one-plus-a-fraction dimensionality are proposed to interpret the correlation. The order factors of the theoretical fits suggest the nanowires of the freshly produced PS have crystalline cores. (C) 1996 American Institute of Physics.