Sofia A. Arzhannikova

Visible photoluminescence from silicon nanopowders produced by silicon evaporation in a high-power electron beam

Silicon nanopowders produced by electron-beam-induced evaporation of a bulk silicon sample in an argon atmosphere are studied by the photoluminescence technique and Raman scattering spectroscopy. A photoluminescence peak in the visible region of the spectrum has been detected at room temperature in powders consisting of silicon nanocrystals. The strong short-wavelength shift of the photoluminescence peak can be attributed to the quantum size effect of electrons and holes in small silicon nanocrystals (about 2 nm). The size of silicon nanocrystals is determined by analyzing Raman spectra, and it is consistent with estimates obtained from photoluminescence data.

Variation in optical-absorption edge in SiNx layers with silicon clusters

Using optical methods, data on optical constants are obtained for silicon nitride films synthesized by plasma-chemical vapor deposition (PCVD). Models for calculating the permittivity in the model of inhomogeneous phase mixture of silicon and silicon nitride are considered. It is found that the optical-absorption edge (Eg) and the photoluminescence peak shift to longer wavelengths with increasing nitrogen atomic fraction x in sinx films. When x approaches the value 4/3 characteristic for stoichiometric silicon nitride Si3N4, a nonlinear sharp increase in Eg is observed. Using Raman scattering, Si-Si bonds are revealed, which confirms the direct formation of silicon clusters during the film deposition. The relation between the composition of nonstoichiometric silicon nitride films, values of permittivity, and the optical-band width is established for light transmission.

Coulomb blockade of the conductivity of SiOx films due to one-electron charging of a silicon quantum dot in a chain of electronic states

The electrical characteristics of metal-oxide-semiconductor (MOS) structures with silicon nanoparticles embedded in silicon oxide have been studied. The nanocrystals are formed by decomposition of an oversaturated solid solution of implanted silicon during thermal annealing at a temperature of ∼1000°C. At liquid-nitrogen temperature, a stepped current-voltage characteristic is observed in a MOS structure consisting of Si nanocrystals in a SiO2 film. The stepped current-voltage characteristic is, for the first time, quantitatively described using a model in which charge transport occurs via a chain of local states containing a silicon nanocrystal. The presence of steps is found to be associated with one-electron charging of the silicon nanocrystal and Coulomb blockade of the probability of a hop from the nearest local state to the conducting chain. The local states in silicon dioxide are assumed to be related to an excess of silicon atoms. The presence of such states is confirmed by measurements of the differential conductance and capacitance. For MOS structures implanted with silicon, the differential capacitance and conductance are found to be higher, compared to the reference structures, in the range of biases exceeding 0.2 V. In the same bias range, the conductance is observed to decrease under ultraviolet irradiation due to a change in the population of the states in the conductivity chains.

Photoinduced Variation of Capacitance Characteristics of MDS Structures with Three-Layer SiNx Dielectrics

Characterisation of three-layer dielectric embedded into MDS-structure (Metal- Dielectric-Silicon) was provided in the dark and under light illumination. In the dark, increasing of differential capacitance, simultaneously, with variation of differential conductivity of MDSstructures was detected. In the light strong changing of capacitance part of impedance was firstly observed, demonstrating decreasing almost to zero values and restoring up to maximal values in narrow bang of voltage applied. Variation of capacitance exceeds significantly so called dielectric layer capacitance, what interpreted as carriers exchanging between substrate and electronic states in SiNx probably due to three-layered kind of its nature.

A model to describe the humplike feature observed in the accumulation branch of capacitance-voltage characteristics of MOS capacitors with oxide-hosted silicon nanoparticles

A model is proposed for description of a humplike feature that was previously observed in the lowfrequency capacitance-voltage (C-U) characteristics of MOS capacitors with oxide layers containing silicon nanoparticles. The formation of this feature is related to variation (at the frequency of measurements) of a charge accumulated in the oxide due to injection of charge carriers from electrodes and their migration by tunneling through oxide along linear chains formed by Si nanoparticles (with a certain spread of tunneling distances in the chain). The adequacy of the model is illustrated with the simple example of metal-oxidesilicon (MOS) capacitor with a planar array of Si nanoparticles in the oxide and a monopolar injection of holes from the accumulation layer of the p-type semiconductor. A C-U curve measured on an MOS capacitor with amorphous Si clusters is presented, which closely resembles curves with a two-hump feature predicted by the proposed model.

Falling down capacitance impedance under light illumination of MDS-structures with three-layer SiNx dielectrics

Characterisation of three-layer dielectric embedded into MDS-structure (Metal-Dielectric-Silicon) was provided in the dark and under light illumination. In the dark, increasing of differential capacitance, simultaneously, with variation of differential conductivity of MDS-structures was detected. In the light strong changing of capacitance part of impedance was firstly observed, demonstrating decreasing almost to zero values and restoring up to maximal values in narrow bands of voltage applied. Variation of capacitance exceeds significantly so called dielectric layer capacitance, what interpreted as carriers exchanging between substrate and electronic states in SiNx probably due to three-layered kind of its nature.

Laser Assisted Formation on Nanocrystals in Plasma-Chemical Deposited SiNx Films

The laser assisted formation of silicon nanocrystals in SiNx films deposited on quartz and silicon substrates is studied. The Raman spectroscopy revealed creation of the Si cluster and crystallite after excimer laser treatments. Photoluminescence signal from the samples was detected at room temperatures. I-V and C-V measurements were carried out to examine carries transfer through dielectrics film as well as recharging of electronics states.

Blue Photoluminescence from Quantum Size Silicon Nanopowder

Silicon nanopowders were produced using electron-beam-induced evaporation of bulk silicon ingots in various gas atmosphere. Optical properties of the nanopowders were studied with the use of photoluminescence and Raman spectroscopy techniques. Photoluminescence peaks in the visible region of the spectrum have been detected at room temperature in silicon nanopowders, produced in argon gas atmosphere. Strong short-wavelength shift of the photoluminescence peaks can be result of quantum confinement effect for electrons and holes in small silicon nanocrystals (down to 2 nm in diameter). The size of silicon nanocrystals was estimated from Raman spectroscopy data. The calculated in frame of effective mass model optical gaps for silicon nanocrystals of spherical shape are in good correlation with experimental photoluminescence data. The attempts of deposition of silicon nanocrystal films from the nanopowders on silicon substrates were carried out.

Special features of the electrical conductivity in doped α-Si:H films with silicon nanocrystals

The electrical properties of undoped and phosphorus-doped α-Si:H films with Si nanocrystals are studied. The silicon nanocrystals are formed by a solid-solid phase transition resulting from the nanosecond effect of a XeCl excimer laser on an amorphous film. The formation of the nanocrystals in the undoped films is accompanied by an increase in the electrical conductivity by two to three orders of magnitude and a simultaneous decrease in the effective activation energy of the conductivity from 0.7 to 0.14 eV. The nanocrystal sizes range from 2 to 10 nm for various laser treatment modes and are determined from Raman scattering data and high-resolution electron microscopy. The temperature dependence of the Fermi level is obtained by calculating the energies of the localized states of electrons and holes in the nanocrystals. It is shown that, as the temperature decreases, the Fermi level tends to the energy of the states in the Si nanocrystals for a wide concentration range of the dopant. The Fermi level’s location close to the states in the nanocrystals is a consequence of the fact that these states are multicharged. It is found that phosphorus effectively transforms into an electrically active state during laser treatment of the doped amorphous Si films, which is an important consideration in the fabrication of shallow p-n junctions and contacts for amorphous Si films.

Direct nitridation of silicon surface by high-density inductively coupled plasma

Ultra-thin silicon oxy-nitride films were created. The films were obtained by using direct N plasma treatment in plasma-chemical reactor with a wide aperture source. Properties of the films were examined by various methods and their good electron quality was confirmed. Features of film growth mechanism are discussed.