EXCITATION OF SIZE-SELECTED NANOCRYSTALLITES IN POROUS SILICON

We prepared silicon that exhibits green-to-red rainbow luminescence al ong the sample, reflecting gradients in the crystallite size. The exci tation has a size-dependent feature, riding a smooth bulklike continuu m. For the size-dependent contribution, we measured absorption band ed ges of 3.75 and 3.0-3.25 eV at the meniscus and opposite end. Excitati on in the meniscus, monitored at the edge of the blue emission, isolat es ultrasmall sizes, with ''excitation coefficients'' quadratic with e nergy, and emission encompassing much of the visible spectrum. Results are discussed in terms of quantum-confinement-induced restructuring o f the diamondlike bonds to form radiative Si-Si surface states. (C) 19 98 American Institute of Physics. [S0003-6951(98)02520-0].