Photoelectric characteristics of silicon carbide–silicon structures grown by the atomic substitution method in a silicon crystal lattice

Data obtained in an experimental study of the photoelectric characteristics of silicon–silicon carbide structures grown by the atomic substitution method on silicon (100) and (111) substrates are presented. It is found that the maximum sunlight conversion efficiency of a silicon–silicon carbide (silicon carbide–silicon) heterojunction is 5.4%. The theory of dilatation dipole formation upon synthesis by the atomic substitution method is used to account for the mechanism of electrical barrier formation at the silicon–silicon carbide interface.     

Integrated amorphous and polycrystalline silicon thin-filmtransistors in a single silicon layer

Using a masked hydrogen plasma treatment to spatially control the crystallization of amorphous silicon to polycrystalline silicon in desired areas, amorphous and polycrystalline silicon thin-film transistors (TFTs) with good performance have been integrated in a single film of silicon without laser processing. Both transistors are top gate and shared all process steps. The polycrystalline silicon transistors have an electron mobility in the linear regime of ~15 cm²/Vs, the amorphous silicon transistors have a linear mobility of ~0.7 cm²/Vs and both have an ON/OFF current ratios of >10⁵. Rehydrogenation of amorphous silicon after the 600°C crystallization anneal using another hydrogen plasma is the critical process step for the amorphous silicon transistor performance. The rehydrogenation power, time, and reactor history are the crucial details that are discussed in this paper     

Recombination of self-trapped excitons in silicon nanocrystals grown in silicon oxide

The kinetics of photoluminescence (PL) and steady-state PL from silicon nanocrystals formed in the SiO₂ matrix by silicon ion implantation were studied experimentally for the first time in the temperature range from liquid-helium to room temperature. A dramatic increase in the photoluminescence decay time, accompanied by PL intensity quenching, is observed below 70 K. The results obtained indicate that the silicon nanocrystal PL arises from radiative recombination of excitons self-trapped at the silicon nanocrystal-SiO₂ interface.     

A permeable-base switching device using stacked layers of silicon, silicon dioxide, and silicon-rich silicon dioxide

A novel permeable-base device that is a type of solid-state analog to the vacuum tube has been-constructed using stacked layers of silicon, silicon dioxide, and silicon-rich silicon dioxide. The base or grid, which is formed from thin patterned polycrystalline silicon with degenerate doping, is separated from a single-crystal silicon substrate that acts as the collector or anode by a layer of silicon dioxide. The emitter or cathode is formed on top of the base using a stack of silicon dioxide, silicon-rich silicon dioxide, and degenerately doped polcrystalline silicon (known as an electron injector structure). Current flow from the emitter to the base and collector is modulated by the electric fields created in the silicon dioxide layers by the voltages applied to the various terminals. This unipolar device, which has only electrons carrying the current, is shown to be capable of operation over a wide range of voltages and gains depending on design.     

Growth of silicon nanoclusters in thermal silicon dioxide under annealing in an atmosphere of nitrogen

It is found for the first time that silicon nanoclusters are formed in the surface layer of thermal silicon dioxide under high-temperature annealing (T = 1150°C) in dried nitrogen. Analysis of the cathodoluminescence spectra shows that an imperfect surface layer appears upon such annealing of silicon dioxide, with silicon nanoclusters formed in this layer upon prolonged annealing. Transmission electron microscopy demonstrated that the silicon clusters are 3–5.5 nm in size and lie at a depth of about 10 nm from the surface. Silicon from the thermal film of silicon dioxide serves as the material from which the silicon nanoclusters are formed. This method of silicon-nanocluster formation is suggested for the first time.     

Charge trapping in ion-sputtered silicon dioxide films on silicon

Charge trapping in thermal silicon dioxide has been previously studied in great detail. Recently there has been an interest in depositing silicon dioxide films at lower temperatures to be compatible with device technologies that are not compatible with the higher temperature. This paper discusses the electron and hole trapping behavior in room temperature, ion-sputtered silicon dioxide thin films. Generally, these films are observed to trap both carriers much more efficiently then thermal silicon dioxide films. The trapping parameters such as the trap cross-section, location, density and the trapping efficiency are reported.     

Multiple bonds in hydrogen-free amorphous silicon

The short-range-order structure and electron paramagnetic resonance of amorphous silicon prepared by vacuum sublimation and by ion implantation are investigated. It is found that amorphous silicon with atoms in the sp ² hybrid state is formed in the annealing of evaporated silicon at 500 °C or in the irradiation of a silicon single crystal with neon at a dose greater than or of the order of 10¹⁷ cm^?2. In the latter case the amorphous material is depthwise inhomogeneous and contains a layered structure consisting of silicon atoms with a period of 5.16 Å. In each case an ESR signal with a g factor g?2.0048, which corresponds to a dangling bond of a silicon atom in the sp ² state, is observed.     

Beyond the silicon roadmap [silicon laser cooling]

We have first developed an all-solid-state 252 nm coherent light source for laser cooling of silicon atoms. This can give an impetus to research into the manipulation of the atomic motion of silicon atoms toward nanoprocess applications. Therefore, we developed an experimental setup for silicon atom manipulation. It was found that a high-quality silicon atomic beam, useful for nanoprocess applications, is obtainable with manipulation using the coherent light source in the system. With this unique apparatus, we continue the challenge to demonstrate the spatial design of nuclear spins of the family of isotopes with laser cooling of Si.     

Diffusion of ytterbium in silicon

Diffusion of ytterbium in silicon is studied by the direct method of radioactive isotopes in the temperature range of 1100–1250°C. Diffusion coefficients of ytterbium impurity in silicon are determined.     

Double-layered silicon nitride antireflection coatings for multicrystalline silicon solar cells

Silicon nitride coating possesses both optical antireflection and electrical passivation effects for crystalline silicon solar cells. In this work, we employed a double-layered silicon nitride coating consisting of a top layer with a lower refractive index and a bottom layer (contacting the silicon wafer) with a higher refractive index for multicrystalline silicon solar cells. Double-layered silicon nitride coating provides a lower optical reflection and better surface passivation than those of single-layered silicon nitride. Details for optimizing the double-layered silicon nitride coating are presented. In order to get statistical conclusions, we fabricated a large number of multicrystalline silicon solar cells using the production line for both the double-layered and single-layered cell types. It was statistically demonstrated that the double-layered silicon nitride coating provided a consistent enhancement in the photovoltaic performance of multicrystalline silicon solar cells over those of the single-layered silicon nitride coating.     

Diffusion of terbium in silicon

The diffusion of terbium in silicon in the temperature range of 1100–1250°C is studied using the direct radioisotope technique for the first time. The diffusion parameters of terbium in silicon are determined.     

Isolation of silicon film grown on porous silicon layer

We have investigated a new technology for dielectric isolation of a Si film grown epitaxially on a porous silicon layer. After oxidation of the porous silicon layer, a Si on Ohcidized Porous Silicon(SOPS) structure can be obtained. It is proposed that micropores pinch off quickly in the interfacial region between the porous silicon layer and the epitaxial film. A minimum yield calculated from Rutherford backscattering spectra of the epitaxial silicon film is 5.3%, and an electron Hall mobility of 600cm²/V.s is obtained in the film with a carrier concentration of 1 x 10¹⁷ /cm³. MOSFETs were fabricated on the SOPS structure.     

Ultra-Shallow junctions in silicon using amorphous and polycrystalline silicon solid diffusion sources

The inter-dependence of diffusion behavior and grain microstructure in amorphous silicon/polysilicon-on-single crystal silicon systems has been studied for rapid thermal and furnace annealing for P and BF₂ implants. It is found that the changes of microstructure during annealing play a major role in determining the diffusion profiles in the substrate as well as in the polysilicon layer. For P doping, a drive-in diffusion results in a much larger grain microstructure for as-deposited amorphous silicon than for as-deposited polysilicon, which leads to the formation of shallower junctions in the substrate for the first case. For B doping, there is little difference in the final microstructure and junction depth between the two cases. The P and B junctions formed in the substrate are found to be laterally very uniform in spite of expected doping inhomogeneities due to polysilicon grain boundaries both for as-deposited amorphous silicon diffusion sources and for as-deposited polysilicon diffusion sources.     

Diffusion of yittrium in silicon

The diffusion of yttrium in silicon is studied for the first time. The diffusion is performed in air or vacuum in the temperature range of 1100–1250°C. The temperature dependence of the diffusivity of yttrium in silicon is described by the relation D = 8 × 10^?3 exp(?2.9 eV/kT) cm² s^?1. The acceptor nature of yttrium in silicon is revealed.     

Growth of nanocrystalline silicon from a matrix of amorphous silicon monoxide

Changes in the structure and phase composition of silicon monoxide in the disproportionation reaction at high temperatures with the formation of a nanocrystalline silicon phase are studied. On itsseparation from the silicon oxides, the nanosilicon powder is subjected to X-ray diffraction analysis and examined by the small-angle X-ray scattering technique. It is found that, under the optimal heat-treatment conditions of silicon monoxide, the powder obtained contains nanosilicon particles with sizes of 17–20 nm and a volume fraction of 40%.     

The silicon PCB

In its simplest form, a silicon hybrid is essentially a miniaturised PCB built on a silicon wafer, and like any other PCB it is made up of layers of metal tracks separated by a suitable dielectric. However, unlike a conventional PCB, a silicon hybrid is manufactured using IC fabrication techniques. The author discusses the Research Initiative in Silicon Hybrids (RISH). Developing silicon hybrids as a viable interconnection technology requires the successful solution of a wide range of problems. There is the obvious issue of developing reliable manufacturing techniques, but silicon hybrids also create their own special demands on chip-to-substrate connection technology, packaging, substrate and IC testing, and computer-aided-design (CAD) software. All these different aspects of silicon-hybrid development are being covered by the RISH project with a view to providing the collaborating companies with a `tool-box' of processes from which the appropriate tool can be selected for a given application     

The effect of cathode materials on reactive ion etching of silicon and silicon dioxide in a CF4 plasma

Silicon and silicon dioxide have been Reactive Ion Etched in a CF₄ plasma using a diode sputtering configuration to achieve etching. Pressures ranged from 20 to 100 millitorr and power densities to the RF cathode were between 0.1 and 1.0 W/cm². The effect of cathode material on the quality of etched surfaces and on etch rates has been investigated. It has been observed that the etch rate of silicon decreases as the area of silicon exposed to the plasma is increased and that this silicon loading effect is strongly influenced by the material covering the balance of the cathode. For instance, the silicon loading effect is much more pronounced when silicon dioxide rather than aluminum is used to cover the balance of the cathode. This silicon loading effect was investigated further by varying RF power. It was found that loading a silicon dioxide covered cathode with silicon wafers decreases the dependence of silicon etch rate on power. The silicon dioxide etch rate and its dependence on RF power are the same whether silicon, silicon dioxide or aluminum is used to cover the balance of the cathode. Possible explanations for these experimental results will be discussed.     

Microlens fabricated in silicon on insulator using porous silicon

In order to realize the planar gradient refractive index (GRIN) microlens which is based upon porous silicon (PSi) and fabricated on silicon on insulator (SOI), a novel anodization method is used by applying lateral electric field. The microlens with smooth variation of the effective optical thickness is achieved. The lens is transparent in the infrared region, including the optical communication window (1.3 μm<λ<1.6 μm). This approach also allows the fabrication of an array of such lenses on SOI, and the GRIN microlens can be used as potential components in future silicon-based integrated optical circuits.     

Solubility of sulfur in silicon

The available published experimental data on the maximum possible concentration of sulfur dissolved in silicon as a function of temperature are analyzed. The authors?? recent results demonstrate that the amount of sulfur dissolved in silicon crystals is approximately two times the reference values, which is in agreement with the data given by a number of other studies.     

Czochralski silicon

When silicon technology was new there were effects and observations which went unused or unrecognized in the rush to get products to market. This paper covers one such set of observations in silicon crystal growth. It has been abstracted from a historical perspective of silicon processing being compiled for family and associates from the experiences of the author.