Silicon Suboxide Layers Research Articles

Simultaneous growth of SiOx/carbon bilayers on Si nanoparticles for improving cycling stability

A soft carbon and silicon suboxide modification strategy is presented to create homogeneous and multilayer core-shell structure silicon-based nanomaterials (Si@SiOx@C). The silicon suboxide layer thickness is homogeneous and can be effectively controlled from 2 to 15 nm through calcining the mesophase pitch-coated silicon nanoparticles at different temperatures. The optimized silicon suboxide thickness of 13.5 nm and a high graphitization degree of carbon allows for good protection of silicon nanoparticles. Correspondingly, quite good cycling performance with a specific capacity of 640 mAh g−1 and a superhigh coulombic efficiency of 99.4% is obtained for Si@SiOx@C anode after 700 cycles at a current of 0.2 A g−1. Si@SiOx@C also exhibits an excellent rate behavior with capacity retention of up to 70.3% when the discharge current increases from 0.05 to 20 A g−1. Such a novel and simultaneous growth of SiOx/carbon bilayers on Si nanoparticles will provide a facile synthesis strategy for the fabrication of high-performance silicon-based anode materials.

Chemical and phase compositions of multilayer nanoperiodic a-SiO x /ZrO2 structures subjected to high-temperature annealing

The chemical and the phase compositions of multilayer nanoperiodic SiO x /ZrO2 structures prepared by vacuum evaporation from separated sources and subjected to high-temperature annealing have been studied by X-ray photoelectron spectroscopy with a layer-by-layer etching. It is found that, under deposition conditions used, the silicon suboxide layers had the stoichiometric coefficient x ~1.8 and the zirconium-containing layers were the stoichiometric zirconium dioxide. It was found, using X-ray photoelectron spectroscopy, that annealing of the multilayer structures at 1000°C leads to mutual diffusion of the components and chemical interaction between ZrO2 and SiO x with predominant formation of zirconium silicate at heteroboundaries of the structures. The SiO x layers of the annealed nanostructures contained ~5 at % elemental silicon as a result of the phase separation and the formation of fine silicon nanocrystals.

Multilayer structures of silicon-suboxide embedded in single crystal silicon

Si/SiOx multilayer structures with ultra-thin silicon-suboxide layers are fabricated with molecular beam epitaxy. The silicon surface is oxidized during growth interruptions at an oxygen pressure between 1.0×10−7mbar and 8.0×10−7mbar. Overgrowth with Si of the oxidized surface is possible for coverages of a few monolayers of O and improves with increasing substrate temperature. X-ray diffraction shows that the silicon layers are single crystalline. Transmission electron microscopy measurements show that the suboxide layers are ~1nm thick, pseudomorph, and exhibit crystalline order throughout the layer. In addition, transmission electron microscopy shows that the oxygen concentration is laterally inhomogeneous. The multilayer structures are thermally very stable, as rapid thermal annealing up to 1000°C shows no influence on the X-ray diffraction patterns.

Wet Chemical Oxidation of Silicon Surfaces Prior to the Deposition of All-PECVD AlO<sub>x</sub>/<i>a</i>-SiN<sub>x</sub> Passivation Stacks for Silicon Solar Cells

Aluminum oxide (AlOx) is currently under intensive investigation for use in surface passivation schemes in solar cells. AlOx films contain negative charges and therefore generate an accumulation layer on p-type silicon surfaces, which is very favorable for the rear side of p-type silicon solar cells as well as the p+-emitter at the front side of n-type silicon solar cells. However, it has been reported that quality of an interfacial silicon sub-oxide layer (SiOx), which is usually observed during deposition of AlOx on Silicon, strongly impacts the silicon/AlOx interface passivation properties [1]. The present work demonstrates that a convenient way to control the interface is to form thin wet chemical oxides of high quality prior to the deposition of AlOx/a-SiNx:H stacks by the plasma enhanced chemical vapor deposition (PECVD).

Laser Micro-Structuring of Fused Silica Subsequent to Plasma-Induced Silicon Suboxide Generation and Hydrogen Implantation

A low-temperature atmospheric pressure plasma jet was used for chemical reduction of fused silica. For this purpose, a hydrogen-containing plasma was applied. A silicon suboxide layer was generated and hydrogen was implanted into the bulk material. Changes in stoichiometry, concentration of hydrogen and optical transmission were determined. An ArF excimer laser was used for the ablation of untreated and plasma-treated fused silica. The ablation threshold was significantly decreased by a factor of 4.6 in case of plasma treated substrates. Furthermore, in multi-pulse experiments, the ablation rate remained constant at least up to a depth of 10.5 μm.

The Effect of Carrier Injection Stress on Boron-Doped Amorphous Silicon Suboxide Layers Investigated by X-ray Photoelectron Spectroscopy

In amorphous silicon solar cells, reducing degradation is one of the key issues in improving cell performance. The degradation of the p-layer can play an important role since it is directly related to the open circuit voltage (Voc) and fill factor (FF) in the cells. In this study, we investigated the changes in boron-doped p-type silicon suboxide (SiOx) layers after carrier injection stress. The boron doping level was varied by controlling B2H6 gas flow rate. When these layers were degraded, the dark conductivity decay decreased from 53% to less than 5%, and the increase in activation energy decreased from 11 to 0.5% depending on the B2H6 gas flow rate increase. Our improvements are explained in conjunction with the three- and four-fold coordinated boron atoms by the shift of the B 1s X-ray photoelectron spectrum. In this paper we present how to improve the stability of hydrogenated amorphous silicon (a-Si:H) thin-film solar cells.

The Effect of Carrier Injection Stress on Boron-Doped Amorphous Silicon Suboxide Layers Investigated by X-ray Photoelectron Spectroscopy

The Effect of Carrier Injection Stress on Boron-Doped Amorphous Silicon Suboxide Layers Investigated by X-ray Photoelectron Spectroscopy

Photocurrent and Photoluminescence of Amorphous Silicon Nanoclusters Embedded in Silicon Suboxide Matrix

We have presented a technique, based on magnetron sputtering of silicon target in the mixture of argon, silane, and oxygen. Addition of oxygen gas was shown to cause formation of silicon suboxide layers with amorphous silicon nanoclusters without subsequent annealing. The layers exhibit significant photoluminescence at room temperature. Their photoluminescence spectra reveal special features predicted in the preceding well-known theoretical works. Heterostructures, fabricated with such layers, show high photocurrent efficiency in short-wavelength spectral region. Our results demonstrate that the investigated structures are promising for photoelectric and photovoltaic applications.

Raman studies of silicon nanocrystals embedded in silicon suboxide layers

Raman spectroscopy is used for the study of SiO x (x ≈ 1) layers subjected to thermal annealing at the temperatures from 950 to 1200°C to form Si nanocrystals inside the layers. From comparison of the experimental data with the model of spatial confinement of phonons, the volume fractions of the crystalline and amorphous Si phases in the layers are determined. It is established that, as the annealing temperature is increased, the average dimensions of Si nanocrystals increase from 4 to 6.5 nm. This is attributed to the coarsening of nanocrystals due to crystallization of the amorphous Si phase and to the processes of coalescence of neighboring nanocrystals at the highest temperatures of annealing.

Ablation of microstructures applying diffractive elements and UV femtosecond laser pulses

A new method for simple and economic fabrication of diffractive optical elements (DOEs) with three and four phase levels, by UV nanosecond (ns) laser ablation is presented. The technique is based on the combination of two sequentially generated complementary 2-level phase elements. During the fabrication, complete ablative removal of a highly absorbing silicon suboxide layer by pixelated backside illumination ensures the necessary high precision and optical quality. Full functionality of the new DOEs is demonstrated by fabricating micro-structures using UV femtosecond pulses.

Phase separation in SiOx films annealed under enhanced hydrostatic pressure

AbstractThe effect of enhanced hydrostatic pressure (HP, (10–12) × 108 Pa) on thermally stimulated phase decomposition of silicon suboxide layers processed at 450–1000 °C was investigated by infrared spectroscopy and photoluminescence measurements. HP stimulates decomposition of non‐stoichiometric SiOx most efficiently at about 450 °C. In spite of enhanced SiOx decomposition, visible photoluminescence appears in HP‐treated samples at higher annealing temperatures in comparison to those annealed under ambient pressure (AP, 105 Pa). Contrary to that, application of HP results in essential enhancement of near‐infrared emission at lower annealing temperatures as compared to processing under AP. This can be related to pressure‐stimulated crystallization of Si inclusions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Control of thermochromic spectrum in vanadium dioxide by amorphous silicon suboxide layer

Vanadium dioxide ( VO 2 ) is a promising candidate for various thermochromic devices. Layering VO 2 film with amorphous silicon suboxide ( a - SiO x ) is an effective approach for controlling the thermochromic spectrum efficiently, since a - SiO x possesses an easily adjustable refractive index over a wide range. However, the crystalline quality of VO 2 is so sensitive to under- and/or over-coated materials that the a - SiO x coatings may be disadvantageous with respect to material suitability. In this study, the controllability of the thermochromic spectrum of VO 2 by employing a - SiO x layer was evaluated under several fabrication conditions and, as a result, it was found that an a - SiO x layer can control thermochromism well without any decline in the stability of VO 2 crystalline growth, which strongly suggests the possibility of expansion in the optical design for efficient thermochromic control.

Conducting two-phase silicon oxide layers for thin-film silicon solar cells

AbstractWe present optical properties and microstructure analyses of hydrogenated silicon suboxide layers containing silicon nanocrystals (nc-SiOx:H). This material is especially adapted for the use as intermediate reflecting layer (IRL) in micromorph silicon tandem cells due to its low refractive index and relatively high transverse conductivity. The nc-SiOx:H is deposited by very high frequency plasma enhanced chemical vapor deposition from a SiH4/CO2/H2/PH3 gas mixture. We show the influence of H2/SiH4 and CO2/SiH4 gas ratios on the layer properties as well as on the micromorph cell when the nc-SiOx:H is used as IRL. The lowest refractive index achieved in a working micromoph cell is 1.71 and the highest initial micromoph efficiency with such an IRL is 13.3 %.

Photoluminescence characterization of silicon nanostructures embedded in silicon oxide

Abstract This paper describes a simple method to analyze the photoluminescent characteristics of materials based on embedded light-emitting nanoclusters. Photoluminescence spectra of deposited silicon sub-oxide layers with the same composition and different thicknesses have been obtained. A saturation of the total luminescence intensity is observed with increase in thickness. By analyzing the photoluminescence spectra several optical and structural parameters can be evaluated. We thus propose a model in which the absorption of light from a nanostructure layer implies the possibility of subsequent luminescence and affects the underlying layers as well. By fitting the data to the developed model, two fundamental parameters are extracted: nanostructures absorption probability, which is independent of the emission energy and the spectra of emission probability of an excited nanostructure which fits a Gaussian shape.

Fabrication of SiO2 Phase Gratings by UV Laser Patterning of Silicon Suboxide Layers and Subsequent Oxidation

UV transparent phase masks are used in various laser applications like fabrication of Bragg gratings in optical fibers or micro patterning by high power laser ablation. Normally they are fabricated by a costly lithographic process including e-beam writing and reactive ion etching. We propose a new fabrication method based on UV laser ablation. The process consists of three steps. First, a silicon suboxide coating (SiOx with x < 2) with a predefined thickness is deposited on a fused silica substrate. Second, due to its strong UV-absorption, this coating can be removed in defined areas by excimer laser ablation at 193 nm or 248 nm leading to the desired phase pattern in form of a binary depth profile. Third, by applying a thermal annealing process, the remaining SiOxcoating is oxidized to UV-transparent SiO2, resulting in a UV-grade surface relief element. The precisely defined interface between substrate and layer allows for ablation with exact depth control and perfect optical surface quality. Such SiO2 phase masks feature a large processed area, high efficiency for VUV to NIR radiation and can be customized e.g. for perfect zero order suppression. Applications of such phase gratings for materials processing with a UV-femtosecond laser are demonstrated. Using the phase gratings in a mask projection configuration, submicron patterns are created in a variety of materials.

Monte Carlo study of interfacial silicon suboxide layers and oxidation kinetics

A simple simulation scheme that simultaneously describes the growth kinetics of SiO 2 films at the nanometer scale and the SiO x /Si interface dynamics (its extent, and spatial/temporal evolution) is presented. The simulation successfully applies to experimental data in the region above and below 10 nm, reproduces the Deal and Grove linear-parabolic law and the oxide growth rate enhancement in the very thin film regime (the so-called anomalous region). According to the simulation, the oxidation is governed mainly by two processes: (a) the formation of a transition suboxide layer and (b) its subsequent drift towards the silicon bulk. We found that it is the superposition of these two processes that produces the crossover from the anomalous oxidation region behavior to the linear-parabolic law.