Optically- induced defects in Si-H nanoparticles

We study the behavior of perfectly hydrogenated Si nanoparticles, under optical excitation. We use semiempirical selfconsistent techniques within the Hartree-Fock formalism, specially parametrized to reproduce key properties of the crystalline environment for the Si atom. We find that the optical absortion spectra of particles ranging in size from 29 to 71 Si atoms evidence both quantum confinement and relaxation effects, with optical gaps in the green-blue region. These particles show however strength for luminescence at much lower energy, related to localised surface defects created by gap-light excitation. These defects involve two surface Si atoms and a H-atom, in a Si-H-Si bridge configuration, and we propose they should be the active luminescent centers in porous Si.We study the behavior of perfectly hydrogenated Si nanoparticles, under optical excitation. We use semiempirical selfconsistent techniques within the Hartree-Fock formalism, specially parametrized to reproduce key properties of the crystalline environment for the Si atom. We find that the optical absortion spectra of particles ranging in size from 29 to 71 Si atoms evidence both quantum confinement and relaxation effects, with optical gaps in the green-blue region. These particles show however strength for luminescence at much lower energy, related to localised surface defects created by gap-light excitation. These defects involve two surface Si atoms and a H-atom, in a Si-H-Si bridge configuration, and we propose they should be the active luminescent centers in porous Si