STRONG OPTICAL NONLINEARITIES IN QUANTUM WIRES AND DOTS OF POROUS SILICON

The increase of transmission at discrete frequencies (bleaching bands) is observed in porous silicon platelets pumped by picosecond laser pulses. it is attributed to a saturation of optical transitions between the energy levels of electrons and holes spatially confined within quasi-zero-dimensional (quantum dots) and quasi-one-dimensional (quantum wires) nanostructures. The results of independent measurements using transmission and reflection electron and scanning tunneling microscopy have confirmed the existence of quantum dots and wires of corresponding size. A considerable slowing of energy relaxation from upper to lower levels of size quantization compared with intraband relaxation in the bulk has been observed in the cooled (80 K) platelets of porous silicon.