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Electrical Properties of Porous Silicon Nanocrystals in a Dielectric Matrix

In this work, the porous silicon nanocrystals were obtained in a dielectric matrix. Porous silicon layers obtained by photoelectrochemical etching of single-crystalline wafers with the [100] and [111] crystallographic orientations were separated from the silicon substrate using epoxy resin. Systems of the porous silicon nanoparticles were characterized by scanning electron microscopy. The dimensions of the silicon nanocrystals varied from several to tens of nanometers in the cross-section. On the basis of comprehensive studies by impedance spectroscopy and thermal activation methods, processes of transfer and relaxation of non-equilibrium charge carriers have been studied. Impedance model of obtained nanosystems was constructed and its electrical parameters were determined. The internal resistance of free-standing porous silicon nanocrystals was more than 10 GOhms and was several orders of magnitude higher than the typical resistance of the porous layer on the silicon substrate. Activation mechanism of charge transport in the 270-350 K temperature range was found and the activation energy of the conductivity was determined. Based on the spectra of thermally stimulated depolarization current, the localized electron states that affect the charge transport in the porous silicon nanosystems were revealed. The calculated energy distribution of the filling density of states has a maximum in the 0.45-0.6 eV energy range. The found trap levels of nonequilibrium carriers are probably related to the electrically active defects at the interface between silicon nanocrystals and the epoxy resin.