G. N. Kamaev

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.

Oxidation kinetics of a silicon surface in a plasma of oxygen with inert gases

The plasma oxidation of a silicon surface in an inductive plasma generation reactor were studied using spectroscopic ellipsometry and atomic emission spectroscopy. The effect of inert gases on the formation kinetics of ultrathin SiO2 films is discussed. The effect of intense oxidation of Si in the plasma formed by nominally pure helium was found. It is suggested that this effect is due to the photostimulated acceleration of the reaction at the silicon-oxide interface by the intrinsic optical emission from the helium plasma.

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.

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.

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.

Formation of silicon nanocrystals in Si—SiO2—α-Si—SiO2 heterostructures during high-temperature annealing: Experiment and simulation

Experiments and simulations are performed to study the formation of silicon nanocrystals (Si-NCs) in multilayer structures with alternating ultrathin layers of SiO2 and amorphous hydrogenized silicon (α-Si:H) during high-temperature annealing. The effect of annealing on the transformation of the structure of the α-Si:H layers is studied by methods of high-resolution transmission electron microscopy, Raman spectroscopy, and photoluminescence spectroscopy. The conditions and kinetics of Si-NC formation are analyzed by the Monte Carlo technique. The type of the resultant crystalline silicon clusters is found to depend on the thickness and porosity of the original amorphous silicon layer located between SiO2 layers. It is shown that an increase in the thickness of the α-Si layer in the case of low porosity leads to the formation of a percolation silicon cluster instead of individual Si nanocrystals.

Influence of irradiation with swift heavy ions on multilayer Si/SiO2 heterostructures

The influence of Xe ions with an energy of 167 MeV and a dose in the range 1012-3 × 1013 cm−2 on heterostructures consisting of six pairs of Si/SiO2 layers with the thicknesses ∼8 and ∼10 nm, correspondingly, is studied. As follows from electron microscopy data, the irradiation breaks down the integrity of the layers. At the same time, Raman studies give evidence for the enhancement of scattering in amorphous silicon. In addition, a yellow-orange band inherent to small-size Si clusters released from SiO2 appears in the photoluminescence spectra. Annealing at 800°C recovers the SiO2 network, whereas annealing at 1100°C brings about the appearance of a more intense photoluminescence peak at ∼780 nm typical of Si nanocrystals. The 780-nm-peak intensity increases, as the irradiation dose is increased. It is thought that irradiation produces nuclei, which promote Si-nanocrystal formation upon subsequent annealing. The processes occur within the tracks due to strong heating because of ionization losses of the ions.

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.

Nanoscale Si/SiO 2 double-barrier structures produced by plasma-chemical technology

Si\SiO2 double-barrier structures with ultrathin nanoscale layers were developed by using α-Si:H thin film depositions and subsequently plasma enhanced oxidation. The experimental equipment with source of wide aperture and high-density inductively coupled RF plasma (ICP) was used. The electrical properties of the manufactured MOS-structures were investigated through measurement of C-V and I–V characteristics. In the experiments we observed the charge effects related to the process of carrier transport through thin dielectric. Furthermore, the areas of differential negative resistance in I–V characteristics were detected. These structures can be used as resonant tunneling diodes.