Influence of silicon cluster on epitaxial growth of silicon carbide

Precursor concentration dependences of growth rate, doping concentration and surface morphology have been investigated in the epitaxial growth of 4H-SiC(0001) epilayers with horizontal hot-wall CVD system using various precursor concentrations under constant C/Si ratio. Form the experimental data it is found that silicon cluster which is formed through gas phase nucleation plays an important role in controlling the doping concentration and epitaxial growth rate of the silicon carbide. It was observed that t...     

Electronic properties of epitaxial 6H silicon carbide

Two comments are made concerning a paper published by Wessels and Gatos with the above title. The first is to assert that weak-field Hall coefficient measurements are more useful in distinguishing singlevalley from multivalley models in a hexagonal crystal than is suggested in the earlier paper. The second is to point out that the mass value which Wessels and Gatos extracted from an analysis of their Hall data as a function of temperature is the total density-of-states effective mass, not the per valley value, as they claimed. Hence the combination of their result and other data does not provide any information concerning the number of valleys in the conduction band of 6H hexagonal SiC.     

Electronic properties of epitaxial 6H silicon carbide

The electrical conductivity and Hall coefficient were measured in the temperature range from 78 to 900 K for n-type epitaxially grown 6H silicon carbide. A many-valley model of the conduction band was used in the analysis of electron concentration as a function of temperature. From this analysis, the density of states mass to the free electron mass ratio per ellipsoid was calculated to be 0.45. It was estimated that the constant energy surface of the conduction band consists of three ellipsoids. The ionization energy of the shallowest nitrogen donor was found to be 105 meV, when the valley-orbit interaction was taken into account. The electron scattering mechanisms in the epitaxial layers were analyzed and it was shown that the dominant mechanism limiting electron mobility at high temperatures is inter-valley scattering and at low temperatures (200 K), impurity and space charge scattering. A value of $\text{360}\text{cm}{}^2\text{V}$ sec was calculated for the maximum room temperature Hall mobility expected for electrons in pure 6H SiC. The effect of epitaxial growth temperature on room temperature Hall mobility was also investigated.     

Influence of the vacuum level upon the growth of carbon nanotubes on silicon carbide surface

We have investigated the influence of the vacuum level upon the growth of carbon nanotubes (CNTs) on 6H-SiC () surface.CNTs of about 160 nm in length were formed densely and uniformly on the 6H-SiC surface during annealing at 1700 °C in a high vacuum (∼10⁻² Pa). CNTs of about 1 μm in length were formed during annealing at 1700 °C in an ultra-high vacuum (∼10⁻⁷ Pa). However, CNTs were not formed and SiO₂ layers were formed on the SiC surface at 1700 °C in air. It is found that longer CNTs can grow up in an ultra-high vacuum, moreover, a little aligned and low-density graphite layers, or carbon nanofibers can also grow up.     

Effect of self-conjugate perforation in amorphous silicon carbide layers

SiC films on glass substrates are found to have an amorphous structure, high insulating properties, and good mechanical strength. The integrated transmission coefficient of the SiC films in the spectral range λ=0.4–0.7 µm depends on their thickness. The SiC films subjected to etching in hydrofluoric acid exhibit self-conjugate perforation.     

Structural defects in 6H-SiC substrates and their effect on the sublimation growth of epitaxial layers in vacuum

The structural perfection of silicon carbide substrates and homoepitaxial layers grown on the substrates by sublimation has been studied by x-ray diffraction (topography and diffractometry) and optical microscopy. The optimum diffraction conditions (hkil reflections, radiation wavelength λ, and recording geometry) for revealing “micropipes” of the dislocation nature are determined. It is shown that the growth conditions used make it possible to obtain highly perfect epitaxial layers.     

Kinetics of the formation of concentrational transitions between epitaxial layers of silicon in the process of growth from a molecular beam

The doping kinetics of an epitaxial layer of silicon growing from a molecular beam is considered, taking mechanisms of impurity-atom capture by the growing layer into account: diffusional capture and immurement by atoms of the basic material. It is shown that, with increase in the growth rate, the thickness of the concentrational transition between regions with different levels of doping rises in the case of predominance of the first mechanism of impurity incorporation in the growing layer and decreases in the case of predominance of the second mechanism. Quantitative estimates of the thickness of the concentrational transition, taking account of the equilibrium coefficients of the impurity distribution between the surface region and the volume of the epitaxial layer, give satisfactory agreement with the experimental results.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 9–12, November, 1982.It remains to thank G. P. Putilov for participation in the work.     

Origin of anomalous electronic structures of epitaxial graphene on silicon carbide

On the basis of first-principles calculations, we report that a novel interfacial atomic structure occurs between graphene and the surface of silicon carbide, destroying the Dirac point of graphene and opening a substantial energy gap there. In the calculated atomic structures, a quasiperiodic 6x6 domain pattern emerges out of a larger commensurate 6 sqrt [3] x 6 sqrt [3]R30 degrees periodic interfacial reconstruction, resolving a long standing experimental controversy on the periodicity of the interfacial superstructures. Our theoretical energy spectrum shows a gap and midgap states at the Dirac point of graphene, which are in excellent agreement with the recently observed anomalous angle-resolved photoemission spectra. Beyond solving unexplained issues in epitaxial graphene, our atomistic study may provide a way to engineer the energy gaps of graphene on substrates.     

High-voltage photovoltaic effect in layers of silicon evaporated in vacuum

Silicon layers which generate a photovoltaic voltage of up to 150 V/cm at room temperature are obtained by evaporation in a vacuum onto an insulating substrate. The spectral characteristics of the voltage, the effect of thermal processing on the value of the voltage and on the resistance of the layers, and the dependence of the voltage on the direction of the illumination and on the structure of the photosensitive layers are investigated. It is concluded that the photosensitive layers of silicon possess a microcrystalline structure with an ordered arrangement of the small crystals, separated by high-resistance oxide-type layers, and are sources of elementary photovoltaic voltages which are added along the layer. It is suggested that the reason for the formation of the elementary photovoltaic voltages is the separation of electron-hole pairs, produced by the light, by the field of the barriers which exist on the surfaces of the individual crystals of the layer and in the gaps between the crystals.The authors thank M. A. Rumsha for help with the electron diffraction investigations and for useful discussions, and also M. I. Rudenok for making the electron microscope investigations.     

Photoluminescence spectra of Sn doped GaAs epitaxial layers: Influence of epitaxial process parameters

Photoluminescence measurements are performed with Sn doped GaAs epitaxial layers $\text{(}\text{n}\text{?}\text{= 4.10}{}^{18}$ to 1.1.10¹⁹ cm^?3) grown from a Sn solution. These samples exhibit the near-bandgap band and four further bands at 1.47, 1.33, 1.2 and 1.08 eV (77K). Their dependence on several parameters of the epitaxial process is studied systematically. The ratio of the peak intensities at 1.33 and 1.47 eV is observed to be influenced by the end temperature, by the growth rate of the layers, and by annealing processes. Comparison is made between the photoluminescence data and the doping concentrations which depend on the same parameters.     

Synthesis of epitaxial silicon carbide films through the substitution of atoms in the silicon crystal lattice: A review

A review of recent advances in the field of epitaxial growth of SiC films on Si by means of a new method of epitaxial substitution of film atoms for substrate atoms has been presented. The basic statements of the theory of the new method used for synthesizing SiC on Si have been considered and extensive experimental data have been reported. The elastic energy relaxation mechanism implemented during the growth of epitaxial SiC films on Si by means of the new method of substitution of atoms has been described. This method consists in substituting a part of carbon atoms for silicon matrix atoms with the formation of silicon carbide molecules. It has been found experimentally that the substitution for matrix atoms occurs gradually without destroying the crystalline structure of the matrix. The orientation of the film is determined by the “old” crystalline structure of the initial silicon matrix rather than by the silicon substrate surface only, as is the case where conventional methods are used for growing the films. The new growth method has been compared with the classical mechanisms of thin film growth. The structure and composition of the grown SiC layers have been described in detail. A new mechanism of first-order phase transformations in solids with a chemical reaction through an intermediate state promoting the formation of a new-phase nuclei has been discussed. The mechanism providing the occurrence of a wide class of heterogeneous chemical reactions between the gas phase and a solid has been elucidated using the example of the chemical interaction of the CO gas with the single-crystal Si matrix. It has been shown that this mechanism makes it possible to grow a new type of templates, i.e., substrates with buffer transition layers for growing wide-band-gap semiconductor films on silicon. A number of heteroepitaxial films of wide-band-gap semiconductors, such as SiC, AlN, GaN, and AlGaN on silicon, whose quality is sufficient for the fabrication of a wide class of micro- and optoelectronic devices, have been grown on the SiC/Si substrate grown by solid-phase epitaxy.     

Development of a model of silicon carbide thermodestruction for preparation of graphite layers

A three-stage scheme of the silicon carbide thermodestruction resulting in surface graphitization, which was proposed earlier (based on structural studies), is discussed. A theoretical analysis shows, however, that this process occurs in two stages, namely, thermodesorption of silicon atoms from the two outer Si-C bilayers followed by condensation of carbon atoms on the Si(0001) face of silicon carbide, thus giving rise to the formation of a two-dimensional graphite structure (graphene).     

Influence of crystallization temperature on growth rate of epitaxial gallium arsenide layers in the system GaAs-AsCl3-H2

Conclusions Thus, consideration of the temperature dependences of the growth rate of singular and vicinal GaAs faces made it possible to determine the activation energy of the growth process in the kinetic region, to demonstrate the changes in the activation energy on passing from singular to vicinal faces, to estimate the magnitude of these changes, and also to analyze some distinctive features of the crystallization process which are related to the crystal chemistry of growing planes. The growth of GaAs epitaxial layers near the <111>B and <001> poles over a wide range of deposition temperatures is limited by the rate of the surface stage while for layers grown on substrates near the <111>A and <110> poles at high temperatures a significant role is played by outward-diffusion limitations which are associated primarily with the arsenic supply.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii., Fizika, No. 9, pp. 101–104, September, 1982.     

Specific features and mechanisms of photoluminescence of nanostructured silicon carbide films grown on silicon in vacuum

The light-emitting properties of cubic silicon carbide films grown by vacuum vapor phase epitaxy on Si(100) and Si(111) substrates under conditions of decreased growth temperatures (T _gr ∼ 900–700°C) have been discussed. Structural investigations have revealed a nanocrystalline structure and, simultaneously, a homogeneity of the phase composition of the grown 3C-SiC films. Photoluminescence spectra of these structures under excitation of the electronic subsystem by a helium-cadmium laser (λ_excit = 325 nm) are characterized by a rather intense luminescence band with the maximum shifted toward the ultraviolet (∼3 eV) region of the spectral range. It has been found that the integral curve of photoluminescence at low temperatures of measurements is split into a set of Lorentzian components. The correlation between these components and the specific features of the crystal structure of the grown silicon carbide layers has been analyzed.     

Epitaxial growth of cadmium telluride films on silicon with a buffer silicon carbide layer

An epitaxial 1–3-μm-thick cadmium telluride film has been grown on silicon with a buffer silicon carbide layer using the method of open thermal evaporation and condensation in vacuum for the first time. The optimum substrate temperature was 500°C at an evaporator temperature of 580°C, and the growth time was 4 s. In order to provide more qualitative growth of cadmium telluride, a high-quality ~100-nm-thick buffer silicon carbide layer was previously synthesized on the silicon surface using the method of topochemical substitution of atoms. The ellipsometric, Raman, X-ray diffraction, and electron-diffraction analyses showed a high structural perfection of the CdTe layer in the absence of a polycrystalline phase.