Tight-binding calculations of the optical properties of Si nanocrystals in a SiO matrix.

We develop an empirical tight binding approach for the modeling of the electronic states and optical properties of Si nanocrystals embedded in a SiO2 matrix. To simulate the wide band gap SiO2 matrix we use the virtual crystal approximation. The tight-binding parameters of the material with the diamond crystal lattice are fitted to the band structure of β-cristobalite.

Tight-binding calculations of SiGe alloy nanocrystals in SiO matrix.

In the empirical tight-binding approach we study the electronic states in spherical SiGe nanocrystals embedded in SiO matrix. For the SiGe alloy and the matrix we use the virtual crystal approximation. The energy and valley structure of electron states is obtained as a function of Ge composition and nanocrystal size.

Thermally stimulated exciton emission in Si nanocrystals.

Increasing temperature is known to quench the excitonic emission of bulk silicon, which is due to thermally induced dissociation of excitons. Here, we demonstrate that the effect of temperature on the excitonic emission is reversed for quantum-confined silicon nanocrystals. Using laser-induced heating of silicon nanocrystals embedded in SiO, we achieved a more than threefold (>300%) increase in the radiative (photon) emission rate.

Red spectral shift and enhanced quantum efficiency in phonon-free photoluminescence from silicon nanocrystals.

Crystalline silicon is the most important semiconductor material in the electronics industry. However, silicon has poor optical properties because of its indirect bandgap, which prevents the efficient emission and absorption of light. The energy structure of silicon can be manipulated through quantum confinement effects, and the excitonic emission from silicon nanocrystals increases in intensity and shifts to shorter wavelengths (a blueshift) as the size of the nanocrystals is reduced.

Nanosecond dynamics of the near-infrared photoluminescence of Er-doped SiO2 sensitized with Si nanocrystals.

We report on an observation of a fast 1.5 microm photoluminescence band from Er3+ ions embedded in an SiO2 matrix doped with Si nanocrystals, which appears and decays within the first microsecond after the laser excitation pulse. We argue that the fast excitation and quenching are facilitated by Auger processes related to transitions of confined electrons or holes between the space-quantized levels of Si nanocrystals dispersed in SiO2.

In-plane electric current is induced by tunneling of spin-polarized carriers.

It has been shown that tunneling of spin-polarized electrons through a semiconductor barrier is accompanied by generation of an electric current in the plane of the interfaces. The direction of this interface current is determined by the spin orientation of the electrons and symmetry properties of the barrier; in particular, the current reverses its direction if the spin orientation changes the sign. Microscopic origin of such a "tunneling spin-galvanic" effect is the spin-orbit coupling-induced dependence of the barrier transparency on the spin orientation and the wave vector of electrons.

Tunneling processes induced by terahertz electric fields.

Tunneling processes induced by terahertz frequency electric fields havebeen investigated.A drastic enhancement of the tunneling probabilityhas been observed by increasing the frequency ω atωτ(e)≫ 1 whereτ(e) is the tunneling time.For a given constant tunneling rate an increase offrequency by a factor of seven leads to a drop of the requiredelectric field strengthby three orders of magnitude.