Anodic etching of p-type cubic silicon carbide

p-Type cubic silicon carbide was anodically etched using an electrolyte of HF:HCl:H₂O. The etching depth was determined versus time with a fixed current density of 96.4 mA cm^–2. It was found that the etching was very smooth and very uniform. An etch rate of 22.7 nm s^–1 was obtained in a 1:1:50 HF:HCl:H₂O electrolyte.     

Homogeneous nanocrystalline cubic silicon carbide films prepared by inductively coupled plasma chemical vapor deposition

Silicon carbide films with different carbon concentrations x(C) have been synthesized by inductively coupled plasma chemical vapor deposition from a SiH(4)/CH(4)/H(2) gas mixture at a low substrate temperature of 500?°C. The characteristics of the films were studied by x-ray photoelectron spectroscopy, x-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared absorption spectroscopy, and Raman spectroscopy. Our experimental results show that, at x(C) = 49?at.%, the film is made up of homogeneous nanocrystalline cubic silicon carbide without any phase of silicon, graphite, or diamond crystallites/clusters. The average size of SiC crystallites is approximately 6?nm. At a lower value of x(C), polycrystalline silicon and amorphous silicon carbide coexist in the films. At a higher value of x(C), amorphous carbon and silicon carbide coexist in the films.     

Relaxing layers of silicon carbide grown on a silicon substrate by magnetron sputtering

Epitaxial layers of silicon carbide of the 3C-polytype are prepared by magnetron sputtering on Si(111) substrates of structural perfection with ω_θ = 1.4°. The crystalline structure and surface morphology of the 3C-SiC/Si(111) heterostructures depending on film thickness are studied by X-ray diffraction, Raman scattering, and atomic-force microscopy. It is found that the additional energy of ionized particles that is imparted to the Si(111) substrate during magnetron sputtering contributes the formation of strong C-C and β-SiC bonds, which hinders the crossing of the grain boundary by dislocations with increasing growth time.     

Nondestructive determination of the characteristics of porous silicon carbide layers

It shown that the porosity and thickness of a porous silicon carbide layer can be nondestructively monitored provided that the sample weight loss upon electrochemical etching is known and the reflectance spectrum exhibits interference.     

Subcritical crack growth in silicon carbide

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Subcritical crack growth in silicon carbide

Crack growth behaviour in two types of commercially available silicon carbide was examined from 600 to 850° C in ambient atmospheres containing oxygen, water vapour, and sulphur dioxide. The double-torsion specimen was used in the incremental displacement rate mode to yield (K ₁,V) relations. The direct-bonded material exhibited unstable crack propagation and arrest behaviour which was not measureably affected by temperature variations or the corrosive environments. The hot-pressed material exhibited subcritical crack growth similar to the three regions of the classical (K ₁,V) diagram. Oxidation of the silicon carbide is suggested to be the mechanism of stress corrosion operating in these environments.     

Effects of substrate doping on the properties of porous silicon carbide layers

Effects of the (n)6H-SiC substrate doping in the interval from 4×10¹⁷ to 4.2×10¹⁸ cm^?3 on the properties of porous silicon carbide layers (pore diameter, relative porosity, pore concentration) were studied for samples prepared by the Lely method. It is established that porous SiC layers obtained by this method in strongly doped substrates are characterized by smaller pore diameter and volume and several times greater pore concentration as compared to analogous values for slightly doped substrates.     

Structural perfection of heteroepitaxial silicon layers grown on sapphire by sublimation-source molecular beam epitaxy

Structurally perfect, single-crystal silicon layers have been grown on \((1\overline 1 02)\) sapphire by sublimation-source molecular beam epitaxy. Electron and x-ray diffraction data demonstrate that silicon-on-sapphire epitaxy occurs at substrate temperatures from 550 to 850°C. As the thickness of the layers decreases from 1.0 to 0.2 μm, their structural perfection degrades. In the layers grown at 600°C, the density of nucleation sites in the initial stages of growth is ? 5 × 10⁹ cm^?2.     

Low-pressure growth of single-crystal silicon carbide

We report on a low-pressure, reproducible process for producing large-area device-quality single-crystal silicon carbide (SiC) on 〈100〉 and 〈111〉 p-type silicon substrates. The process has been used to produce epitaxial layers up to 20 μm thick, and 2″ in diameter. The unintentional doping (n-type) was in the 10¹⁷ cm⁻³ range with mobilities of several hundred cm²/V s.     

Applications of microcrystalline hydrogenated cubic silicon carbide for amorphous silicon thin film solar cells

We demonstrated the fabrication of n-i-p type amorphous silicon (a-Si:H) thin film solar cells using phosphorus doped microcrystalline cubic silicon carbide (μc-3C-SiC:H) films as a window layer. The Hot-wire CVD method and a covering technique of titanium dioxide TiO₂ on TCO was utilized for the cell fabrication. The cell configuration is TCO/TiO₂/n-type μc-3C-SiC:H/intrinsic a-Si:H/p-type μc- SiC_x (a-SiC_x:H including μc-Si:H phase)/Al. Approximately 4.5% efficiency with a V_oc of 0.953 V was obtained for AM-1.5 light irradiation. We also prepared a cell with the undoped a-Si_1−xC_x:H film as a buffer layer to improve the n/i interface. A maximum V_oc of 0.966 V was obtained.     

The features of photoluminescence from nanograins of gallium-doped cubic silicon carbide

The photoluminescence (PL) and photoexcitation spectra of carbonized porous silicon (por-Si) doped with gallium in the course of a high-temperature annealing were studied. It is shown that carbonization leads to the formation of a heterojunction between 3C-SiC nanograins and silicon quantum wires. The spectrum of PL from gallium-doped silicon carbide nanograins is shifted by 0.35 eV toward higher energies relative to the spectrum of bulk por-Si and exhibits several features related to the radiative annihilation processes involving phonons and donor-acceptor (N-Ga) pairs. The PL excitation spectra of carbonized por-Si display two resonance bands with the energies E ₁=2.8–3.1 eV and E ₂=3.2–3.7 eV.     

On the growth mechanism of silicon carbide whiskers

The microstructure of SiC whiskers has been studied through analytical electron microscopy. The whiskers were found to contain discrete regions of high and low planar defect density. These regions of low defect density were identified as 3C beta-SiC, whereas the regions of high defect density were consistent with a mixture of SiC polytypes, with the 3C and the 6H polytypes being the most predominant as a result of the formation of a high density of microtwins on the (1 1 1) planes perpendicular to the 〈1 1 1〉 growth direction. A growth mechanism is suggested based on observations of (a) outer layers of SiC on vapour-liquid-solid catalysts and (b) C∶Si variations between the regions of high and low densities of planar defects. It appears that there is some degree of stoichiometric control over the microstructure of the SiC whiskers in that slight carbon enrichments seem to promote the growth of relatively defect-free regions of beta-SiC whiskers.     

Morphology and optical properties of titanium-doped porous silicon carbide layers

The effect of rapid thermal annealing (RTA) in oxygen on the properties of titanium-doped porous silicon carbide (por-SiC) layers has been studied. The data on the surface morphology and the photoluminescence (PL) spectra show that the high-temperature diffusion annealing is accompanied by the formation of titanium silicides, by an increase in the grain size of the material, and by the emergence of pores on the surface of the por-SiC-Ti sample. The results of PL measurements are consistent with data on the phase composition and the surface morphology of the samples. It is established that RTA leads to modification of the titanium-doped por-SiC structure.     

Initial stages of the MBE growth of silicon carbide nanoclusters on a silicon substrate

The growth of silicon carbide (SiC) nanoclusters by molecular beam epitaxy on silicon substrates has been studied using a combination of experimental and theoretical methods. The first results concerning the initial stages of this growth are presented.     

13. Measurement of the lattice constant of SiGe heteroepitaxial layers grown on a silicon substrate

The lattice constant of thin heteroepitaxial layers composed of single crystal SiGe solid solutions various compositions grown on silicon substracts were measured. The measurements were performed by X-ray diffraction method. The fact that the layers are thin and, therefore, there is also reflection from the silicon substrate (in addition to the reflection from the layer) is utilized for this measurement method. A review of the measurement method is given and the experimental results obtained by irradiating the samples with CuK_α are presented. Specific problems related to the measurement methods and to the layer lattice structure are also presented. There are: resolution problems between the reflections from the layer and the substrate for low Ge concentrations, deformation problems, the effects of the defects and non-uniform changes in the lattice constant at different crystallographic orientations.     

The effect of hydrogen etching on the electrical properties of autoepitaxial silicon carbide layers

Experimental data showing that preliminary hydrogen etching of a SiC substrate influences the concentration of donors or acceptors in autoepitaxial SiC layers are presented. The impurity concentration in the epitaxial layers grown on etched and unetched substrates may differ by an order of magnitude. A physical explanation of the observed correlation is proposed. The importance of the effect of competitive etching on the epitaxial growth is pointed out.     

Room-temperature formation of low refractive index silicon oxide films using atmospheric-pressure plasma

This study aims to apply atmospheric-pressure (AP) plasma to the fabrication of single-layer anti-reflection (AR) coatings with porous silicon oxide. 150 MHz very high-frequency (VHF) excitation of AP plasma permits to enhance the chemical reactions both in the gas phase and on the film-growing surface, increasing deposition rate significantly. Silicon oxide films were prepared from silane (SiH4) and carbon dioxide (CO2) dual sources diluted with helium. The microstructure and refractive index of the films were studied using infrared absorption and ellipsometry as a function of VHF power density. It was shown that significant increase in deposition rate at room temperature prevented the formation of a dense SiO2 network, decreasing refractive index of the resulting film effectively. As a result, a porous silicon oxide film, which had the lowest refractive index of 1.24 at 632.8 nm, was obtained with a very high deposition rate of 235 nm/s. The reflectance and transmittance spectra showed that the low refractive index film functioned as a quarter-wave AR coating of a glass plate.     

Polycrystalline silicon film growth in a SiF4/SiH4/H2 plasma

The growth of polycrystalline silicon (polysilicon) films from SiF₄/SiH₄/H₂ gas mixtures is reported. The polysilicon films have been deposited in a multi process reactor by a PECVD process. The effect of r.f. power, chamber temperature and gas flow ratios on grain size and deposition rate have been determined. The fluorine concentration and the grain sizes of the films have been determined by SIMS and atomic force microscopy (AFM), respectively. Grain sizes in excess of 900 Å are reported for layers deposited at 300°C.     

Investigation of implanted layers in silicon carbide by a modulation photoreflection method

The possibility of using a modulation photoreflection method for diagnostics of ion-implanted layers in silicon carbide is considered. It is shown that the photoreflection method can be used to determine the layer thickness and also the variation in the optical parameters of the layer as a function of the implanted ion dose. Pis’ma Zh. Tekh. Fiz. 23, 11–20 (July 12, 1997)