A. N. Kholod

Grain interaction effect in electronic properties of silicon nanosize films

Electronic properties of both nanometer thickness (111) monocrystalline and nanocrystalline free standing silicon films were calculated within a self-consistent linear combination of atomic orbitals method. Grained nature of the nanocrystalline films is found to induce both a direct band gap and its reduction (down to about 2 eV) with respect to an isolated grain of same size.

Carrier transport and related phenomena in nanosize periodic silicon/insulator structures

Abstract Experimental facts and theoretical models describing mechanisms of carrier transport across silicon/insulator quantum wells are reviewed. Single and multi quantum wells (MQW) formed in periodic Si/CaF 2 and Si/SiO 2 nanostructures are mainly covered. Carrier traps in the barrier material (CaF 2 , SiO 2 ) are shown to have dramatic influence on electron and hole tunneling through the barriers. When the carrier energy coincides with local trap levels, the carrier transport gets the resonant character, otherwise the effects caused by charging of the traps dominate. As a result, a region of negative differential resistance (NDR) and memory (hysteresis) effect become typical for I – V curves of the structures. Intensity of electroluminescence is shown to be mediated by the competition between radiative recombination and non-radiative Auger processes in the wells. Novel applications of periodic quantum well nanostructures are considered.

Electroluminescence simulation of multiquantum well silicon structures

A model of electroluminescence from the multiquantum well structure formed by alternated nanosize layers of silicon (Si) and calcium fluoride (CaF2) is proposed. Electron and hole tunneling through the CaF2 barriers is supposed to occur via Wentzel–Kramers–Brillouin mechanism. Carrier interband recombination in the Si wells is considered to produce photons. A simulation of current–voltage characteristics and luminescence properties is performed taking into account the geometry of the structure and the fundamental physical parameters of the materials involved. The electroluminescence is found to be characterized by a maximum intensity depending on the number of periods in the multiquantum wells. The electroluminescence intensity shows also a nonmonotonous dependence on the recombination coefficient and carrier concentration at the contacts.

Cascaded resonant tunneling diode quantizer for analog-to-digital flash conversion

We propose and model an application of cascaded resonant tunneling diodes to flash analog-to-digital conversion. We connect diodes of linearly increasing area in series, with separate contacts to interconnecting doped layers between the diodes. When a voltage is applied to the structure, the linearly changing diode size determines which of the diodes switch to the valley current, while the interconnecting contacts allow for a differential voltage measurement that accomplishes the signal quantization. The resulting flash quantizer has an estimated frequency operating limit in the gigahertz range.

Vertical electrical transport in Si/CaF2 nanocrystalline heterostructures

Abstract Simple devices constituted by CaF2 barriers and one or two Si wells were fabricated on p+ substrates and characterized electrically at room temperature. Current–voltage characteristics present two specific features: a shift of the voltage at zero-current and a negative differential resistance behaviour for reverse bias conditions. The former is explained well by means of a simple equivalent circuit. The latter is more complicated and we suggest that it could be explain in terms of a model considering trapping of the carriers on defect centers.