Quantum confinement in nanocrystalline silicon

Quantum confinement effects in different kinds of nanocrystalline silicon systems are experimentally and theoretically investigated. Porous silicon structured as a nanowire network and silicon nanodots embedded in amorphous silicon dioxide are studied. The main quantum confinement effect in both cases is represented by the appearance of new energy levels in the silicon band gap. The corresponding energies can be experimentally determined from the current - temperature characteristics, which show an Arrhenius-like behavior. The curves present several activation energies between liquid nitrogen temperature and room temperature. The energy levels can be evaluated from a quantum well model. The fundamental level is located at the top of the valence band. The change of the activation energy is then related with the filling of the levels. The ratios of the consecutive activation energies in the current - temperature characteristics prove that the excitation undergoes the angular momentum conservation law imposed by the applied electric field. The estimation of the mean size of the nanocrystals from the values of the activation energies is in good agreement with the microstructure investigations performed on the samples. The confinement levels are also in good agreement with the photoluminescence measurements..