Electroluminescence stabilization of nanocrystalline porous silicon diodes

NRC publication: Ye

First-Principles Study of the Band Gap Structure of Oxygen-Passivated Silicon Nanonets

A net-like nanostructure of silicon named silicon nanonet was designed and oxygen atoms were used to passivate the dangling bonds. First-principles calculation based on density functional theory with the generalized gradient approximation (GGA) were carried out to investigate the energy band gap structure of this special structure. The calculation results show that the indirect–direct band gap transition occurs when the nanonets are properly designed. This band gap transition is dominated by the passivation bonds, porosities as well as pore array distributions. It is also proved that Si–O–Si is an effective passivation bond which can change the band gap structure of the nanonets. These results provide another way to achieve a practical silicon-based light source

Carrier transport mechanisms in cathodically biased meso-porous p/sup +/-Si against solutions containing Fe/sup 2+/ and Co/sup 2+/ species

This work reports on the use of the cyclic voltammetry technique to study the electrochemical behavior of porous p/sup +/-type silicon (PS) contacted by aqueous solutions containing Fe/sup 2+/ and Co/sup 2+/electro-actives species. Current-potential (I-V) measurements were performed on both flat and porous silicon substrates and different Fe/sup 2+/ concentrations were considered. With flat Si, similar I-V characteristic behaviors were obtained in 0.1 M Fe/sup 2+/ and 0. 1 M Co/sup 2+/ solutions, except that iron can be deposited from a potential more cathodic than cobalt. With porous Si, different I-V characteristic behaviors were observed and a diffusion-like current peak was detected in the presence of Fe/sup 2+/ species. The observed current peak is located near the standard redox potential of iron. However, its intensity is lower than that of Fe/sup 2+/ ions diffusion current peak and it does not increase as Fe/sup 2+/ concentration increases. A three-step carrier transport mechanism was proposed to show that the current peak could be attributed to iron nucleation on the pore walls via electroless deposition. Accordingly the difference observed in PS I-V characteristics was attributed to the fact that electroless deposition on pore walls occurs at a potential for which the reduction of Co/sup 2+/ ions is faster than that of Fe/sup 2+/ ones and it can also occur at the pore bottom via electrodeposition. These results are used to explain the poor pore filling rate with iron, reported elsewhere.Anglai