Pulsed measurements on the solid-electrolyte system, which proved very useful in the study of crystalline semiconductors, have been found to be equally effective when applied to hydrogenated amorphous Si films. Here, as well, the aSi:H/electrolyte interface is essentially blocking to current flow and, as a result, surface space-charge layers, ranging from large depletion to very strong accumulation conditions, can be induced and studied. In particular, valuable information can be gained on the density of the localized bulk states. Measurements in the depletion range under illumination yield directly the total density of occupied states in the entire energy gap. This is very useful in obtaining a quick and reliable assessment of the quality of the amorphous films. In high-grade films we find that the total density of occupied states is around 1018 cm−3. The data in the accumulation range, on the other hand, provide useful information on unoccupied states near the conduction band edge. The blocking nature of the amorphous Si/electrolyte interface is utilized also to apply a sweep-out technique for an accurate determination of μτ the product of the electron mobility and lifetime, even when this value is very low. In a rather poor-quality film, for example, we find μτ to be 5 × 10−8 cm2/V.

For quite a few systems in the continuum, such as carbon nanotube polymer composites and segregated composites, percolation electrical conductivity exponents that are much smaller than the universal value have been reported. This is unexpected in view of the classical lattice percolation theory. Here we provide a simple general phenomenological model that accounts for such observations within the framework of universality. We suggest that these small value exponents are due to the interplay between the connectivity and the structural variations that follow the increase of the fractional volume content of the conducting phase.

RF magnetron sputtering of two separate silicon and oxide (SiO2 or Al2O3) targets in pure argon plasma was used for deposition of Six(SiO2)1-x and Six(Al2O3)1-x films with x=0.15-0.7 on long fused quarts substrate. The effect of post-fabrication treatments on structural and light emitting properties of the films with different x values was investigated by means of Raman scattering, electron paramagnetic resonance and X-ray diffraction as well as by photoluminescence (PL) methods. The formation of amorphous Si clusters upon deposition process was found for the both types of films. The annealing treatment at 1150°C during 30 min results in formation of Si nanocrystallites (Si-ncs). The latter were found to be larger in Six(Al2O3)1-x films than that in Six(SiO2)1-x counterparts with the same x values and are under tensile stresses. The investigation of photoluminescence properties of annealed films of both types revealed the appearance of visible-near infrared light emission. The Six(SiO2)1-x films demonstrated one broad PL band which peak position shifts gradually to from 1.4 eV to 1.8 eV with the x decrease. Contrary to this, for the Six(Al2O3)1-x films two overlapped PL bands were observed in the 1.4-2.4 eV spectral range with peak positions at ~2.1 eV and ~1.7 eV accompanied by near-infrared tail. Comparative analysis of PL spectra of both types samples showed that the main contribution to PL spectra of Six(SiO2)1-x films is given by exciton recombination in the Si-ncs whereas PL emission of Six(Al2O3)1-x films is caused mainly by carrier recombination either via defects in matrix or via electron states at the Si-ncs/matrix interface.

We studied the tunneling percolation conductivity dependence on the site or bond occupation probability in the square lattice. The model predicts that in both, lattice and continuum systems in which there is a hierarchy of the local conductances, the dependence of the global conductivity on the site or volume occupation probability will yield a conductivity staircase. In particular we evaluate the implications of the staircase on the critical behavior of the conductivity. We then show experimental evidence for the predicted percolation-tunneling staircase in a Ag-Al 2 O 3 granular metal system and in a carbon black-polymer composite. Following that, we propose that for carbon nanotube (CNT) polymer composites the data in the literature give ample support to a percolation-dispersion staircase behavior. The implication of the present findings on the percolation-hopping problem in composite materials is also discussed.

Layers grown by magnetron deposition of Si and SiO2 on a p-type silicon substrate and containing silicon nanocrystals in the oxide matrix have been studied by the method of temperature dependences of the capacitive photovoltage. The effect of the substrate orientation and natural oxidation preceding high-temperature annealing that results in the formation of Si nanocrystals in the SiO2 matrix on the layer-substrate interface characteristics is studied. The density of fast interface states trapping majority carriers was estimated. It is found that structural changes occur at the layer-substrate interface in the case of a (111) substrate and are caused by stresses appearing upon cooling. It was shown that natural oxidation of the deposited layer, preceding high-temperature annealing, causes an increase in the charge trapped in the oxide.

Si-rich-SiO2 layers with excess silicon of 45–50% were grown by RF magnetron co-sputtering from pure SiO2 and Si targets and were studied by Raman scattering, HRTEM, electron-paramagnetic resonance and X-ray diffraction (XRD) methods as well as by photo-voltage technique operated at different temperatures. The effect of Si substrate orientation of (111) or (100) on the layers properties was investigated. It was shown that high-temperature annealing in inert atmosphere stimulates a formation of Si crystallites in the film volume and of quartz crystallites near the layer/substrate interface. The dependences of the space orientation and the total volume of the formed quartz crystallites on substrate orientation were observed. The concentration of quartz crystallites in the films grown on the (100) Si substrate was found to be higher in several times than that in the films grown on the (111) Si substrate. The effect of the mechanical stresses on the layer–substrate interface states was observed for the layer prepared on the (111) Si substrate. It was shown that the natural oxidation of the layers before the annealing at high-temperature results in an increase of the positive fixed charge in the layer. At the same time it was found the formation of EX-centers containing Si vacancies close to crystallite/matrix interface.

SiOx layers with lateral composition gradient (co-layers), formed by co-sputtering in argon plasma from Si and SiO2 targets, were investigated both before and after high temperature annealing using IR absorption and Raman scattering. For all coordinates we found more oxygen in the co-layers than the oxygen amount in SiO2 layers sputtered from quartz target only. It was found that the quartz target surface in the plasma heats up and this may result in oxygen and silicon monoxide fluxes. The capture of this additional oxygen by the silicon flux during co-sputtering may be the reason for the excess oxygen in the co-layers. For samples with low silicon content (x > 1), upon annealing a complete phase separation of SiOx into SiO2 and Si takes place. In SiOx films with high Si content some of the silicon is in the crystalline phase even before annealing.

Si-rich- SiO2 layers with high excess Si content grown by radio-frequency magnetron sputtering were studied by Raman scattering, X-Ray diffraction, electron paramagnetic resonance, and photoluminescence methods. It was found that high temperature annealing stimulates the formation of Si crystallites with preferred orientation in 〈111〉 direction. It was shown that the effect of crystallites orientation depends on excess Si content. Besides, comparable contribution of amorphous and crystalline silicon phases in the structure was observed for the annealed layers with Si excess more than 55%. It was observed that both crystalline and amorphous Si inclusions give the essential contribution to the photoluminescence spectra.

Si-SiO2 layers with high excess Si content prepared by magnetron co-sputtering of Si and SiO2 and subsequently annealed were studied by electron paramagnetic resonance and photoluminescence methods. It was shown that adding oxygen during the deposition run or aging in air of as-deposited films influences the characteristics of the oxide layer surrounding the silicon crystallites. It was found that for layers with more than 55 vol.% of excess silicon the silicon crystallites are oriented. After high-temperature annealing not all the excess silicon was in crystalline form but part of it was in the amorphous phase. The depth distribution of the crystallites was found to be homogeneous while the distribution of amorphous silicon has a maximum around the middle of the layer. (C) 2009 Elsevier B.V. All rights reserved.

Deposition of SiO x layers of variable composition onto silicon wafers was performed by co-sputtering of spaced Si and SiO 2 targets in argon plasma. Coordinate dependences of the thickness and refractive index of separately deposited Si and SiO 2 layers and the SiO x layer grown during co-sputtering of targets were determined using optical techniques. It was shown that the SiO x layer composition is not equal to a simple sum of thicknesses of separately deposited Si and SiO 2 layers. The coordinate dependences of the Si and SiO 2 layer thicknesses were calculated. To fit the calculated and experimental data, it is necessary to assume that no less than 10% of silicon is converted to dioxide during co-sputtering. A comparison of the coordinate dependences of the IR absorbance in SiO 2 and SiO x layers with experimental ellipsometric data confirmed the presence of excess oxygen in the SiO x layer. Taking into account such partial oxidation of sputtered silicon, composition isolines in the substrate plane were calculated. After annealing of the SiO x layer at 1200°C, photoluminescence was observed in a wafer area predicted by calculations, which was caused by the formation of quantum-size Si nanocrystallites. The photoluminescence intensity was maximum at x = 1.78 ± 0.3, which is close to the composition optimum for ion-beam synthesis of nanocrystals.

Structural and light emission properties of Si-rich SiO2 layers with high excess Si content grown by radio-frequency magnetron sputtering were studied by Raman scattering, X-ray diffraction, electron paramagnetic resonance and photoluminescence methods. After high temperature annealing of the layers with Si excess more than 55% comparable contribution of amorphous and crystalline silicon phases in the structure was observed. Besides, the preferable orientation of Si crystallites in 〈111〉 direction was found for the layers grown on both silicon and quartz substrates. It was shown that the effect of crystallites orientation depends on excess Si content. It was observed that both crystalline and amorphous Si inclusions give the essential contribution to the photoluminescence spectra.

The properties of SiOx layer prepared by magnetron sputtering is studied by photoluminescence Auger and SIMS methods. The depth distribution of emission characteristics and chemical composition is obtained. It is shown that as-sputtered SiOx layers are non-emitted and characterized by homogeneous enough chemical composition. High-temperature annealing in nitrogen atmosphere stimulates not only the Si nanocrystal formation but also the redistribution of silicon and the appearance of Si depleted region near layer-substrate interface. The last process is found to be dependent on excess Si content. It is found that decrease of silicon content in the depth of annealed layers is followed by the decrease of particle sizes that is proved by the blue shift of photoluminescence maximum. The possible reasons of the appearance of Si depleted region are discussed.

The effect of preparation conditions and annealing treatment on Si-rich-SiOx layers was investigated. It was observed that oxygen plays important role in the creation of light-emitting centres. It was found that the emission in the green-orange spectral range is connected with silicon oxide defects which contain dangling bonds. At the same time PL band in the infrared spectral range is caused by recombination of carriers in amorphous silicon or nanocrystalline one. It is shown that modification of defect content under various treatments gives the possibility to control the emission properties of the layers.

The system of silicon nanocrystals embedded in SiO2 was characterized by electrical measurements depending on the excess Si content in oxide ranged from 6 to 74%. Electron transport through the oxide after percolation transient demonstrates the activation character of current at T > 230 K with activation energy from 2.1 eV near percolation threshold and down to 0.1 eV for higher Si content. The variable range hopping conductivity strongly depended on the excess Si content was observed at lower temperatures.

The process of thermal decomposition of SiOx, layers prepared by magnetron sputtering is studied by photoluminescence, AFM, Auger and SIMS methods. The dependence of the depth distribution of the chemical composition on excess silicon content is obtained. It is shown that as-sputtered SiOx layers are characterized by homogeneous enough chemical composition and do not exhibit photoluminescence. High-temperature annealing in nitrogen atmosphere stimulates not only Si nanoparticle formation but also the appearance of a Si depleted region near layer-substrate interface. This last process is found to be dependent on excess Si content. The decrease of silicon content in the depth of the annealed layers is accompanied by the decrease of Si particle sizes as proved by the blue shift of the photoluminescence maximum. The mechanisms of SiOx decomposition and possible reasons for the appearance of the Si depleted region are discussed. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Wemheim.

The process of thermal decomposition of SiOx layers prepared by magnetron co-sputtering of Si and SiO2 on Si and quartz substrates is studied by Auger and secondary ion mass spectroscopies. It is found that high temperature annealing of the layers causes a Si-depleted region near the layer/substrate interface. It is shown that the formation of this region does not depend on the type of substrate but depends on the content of excess Si and is observed at high content of excess Si. When the excess Si content decreases, the Si-depleted region at first smears and then disappears. The mechanism of SiOx decomposition and possible reasons for the appearance of the Si-depleted region are discussed.

The samples with layer of silicon nanocrystals ncSi embedded in SiO2 (the excess Si content in oxide ranged from 5 to 92%) were subjected to high energy ion implantation. Implantation-induced modification of SiO2-ncSi properties discussed in the report includes a shift of the ncSi-related photoluminescence peak and change in charge value trapped on the nanocrystals.

This paper presents the results of photoluminescence, its temperature dependence and Raman scattering investigations on magnetron co-sputtered silicon oxide films with (or without) embedded Si (or Ge) nanocrystallites. It is shown the oxide related defect origin of the visible PL centers peaked at 1.7, 2.06 and 2.30 eV. The infrared PL band centered at 1.44–1.58 eV in Si–SiOx, system has been analyzed within a quantum confinement PL model. Comparative PL investigation of Ge–SiOx system has confirmed that high energy visible PL bands (1.60–1.70 and 2.30 eV) are connected with oxide related defects in SiOx. The PL band in the spectral range of 0.75–0.85 eV in Ge–SiOx system is attributed to exciton recombination inside of Ge NCs.

The photoluminescence and electrical properties are compared for silicon-oxide layers containing Si nanocrystals and having different Si content. The oxide was deposited by co-sputtering of silicon dioxide and silicon with the subsequent annealing for the formation of nanocrystals. Excess Si content in the layer varies along the sample from 6 to 74 vol %. It is found that a charge magnitude determined from the flat-band voltage has a pronounced peak for the excess Si content of about 26%, the largest charge correlating with the highest photoluminescence intensity. The further increase in the excess Si content in oxide leads to a decrease in both the oxide charge and the photoluminescence intensity and to the appearance of percolation conductivity.