PHOTOEXCITATION OF SI-SI SURFACE-STATES IN NANOCRYSTALLITES

Intrinsic localized radiative surface states belonging to Si-Si dimers on the surface of silicon nanocrystallites have been recently predict ed. We examine the various photoexcitation pathways involved in popula ting these molecular states. We include both direct excitation from th e ground state and indirect excitation from the photoexcited delocaliz ed excitonic states via quantum tunneling and thermal activation. We d etermine the absorption and excitation spectra and the quantum efficie ncy of the photoluminescence as a function of the crystallite size. Ou r calculation gives a dramatic enhancement in the efficiency for sizes below a critical size of about 1.4 nm.