Porous thin films grown from size-selected silicon nanocrystals

Size-selected silicon nanocrystals (Si-nc) with diameters d ≈ (5–6) nm, prepared in a flow reactor by CO2-laser-induced SiH4 decomposition and showing strong photoluminescence in the visible regime after oxidation of their surface, have been accumulated as thin films on quartz substrates. These films also contain clusters of agglomerated Si-nc which conserve the electronic properties of the single Si-nc such as the compression of the electronic wave function and show a similar size distribution of Si-nc as the porous Si-nc layer underneath, which has been verified by spectral photoluminescence measurements. The porosity has been modelled by Monte Carlo computer simulations within a simple stick-ball approach for the local arrangement of the Si-nc versus film growth time to (85.6 ± 0.8)% which reasonably agrees with an earlier experimental result. Simultaneously with growth of porous thin films we have recorded charge transport in coplanar contact arrangement showing three regimes: i) negligible contribution at the beginning of film growth due to missing connections, ii) a percolation type of superlinear increase of current with exponent 3 / 2, and iii) linear increase with further film thickness.