Face Of Silicon Carbide Research Articles

Effect of Polar Faces of SiC on the Epitaxial Growth of Graphene: Growth Mechanism and Its Implications for Structural and Electrical Properties

In this study, epitaxial graphene layers of cm2 sizes were grown on silicon carbide (SiC) substrates by high-temperature sublimation. The behavior of the two crystallographic SiC-polar faces and its effect on the growth mechanism of graphene layers and their properties were investigated. Crystallographic structural differences observed in AFM studies were shown to cause disparities in the electrical conductivity of the grown layers. On the silicon-polar (Si-polar) face of SiC, the graphene formation occurred in spike-like structures that originated orthogonally from atomic steps of the substrate and grew outwards in the form of 2D nucleation with a fairly good surface coverage over time. On the carbon-polar (C-polar) face, a hexagonal structure already formed at the beginning of the growth process. On both polar faces, the known process of step-bunching promoted the formation of nm-scale structural obstacles. Such a step-bunching effect was found to be more pronounced on the C-polar face. These 2D-obstacles account for a low probability of a complete nano-sheet formation, but favor 2D-structures, comparable to graphene nanoribbons. The resulting direction-dependent anisotropic behavior in electrical conductivity measured by four-point probe method mainly depends on the height and spacing between these structural-obstacles. The anisotropy becomes less prudent as and when more graphene layers are synthesized.

The role of charge distribution on the friction coefficients of epitaxial graphene grown on the Si-terminated and C-terminated faces of SiC

The friction coefficients of single-layer epitaxial graphene grown on the Si-terminated and C-terminated faces of Silicon Carbide (SiC) substrate were measured under ambient conditions using Friction Force Microscope (FFM). The lateral friction force measurements acquired in the applied normal force range between 4.0 and 16.0 nN showed that the friction coefficient of graphene on the C-terminated face of SiC is about two times smaller than the one grown on its Si-terminated face. The lateral friction was found to be decreased as the average of root mean square roughness increases suggesting the observed difference in the friction coefficients cannot be related to the roughness of the graphene layers. DFT calculations demonstrated that the altered periodicity of charge distribution on graphene due to the specific interactions with two distinct polar faces of SiC substrate might explain the observed difference in the friction coefficients.

Structural Strain in Single Layer Graphene Fabricated on SiC

Single layer graphene is fabricated on the Si face of silicon carbide through thermal decomposition. The thickness of graphene was checked by a combination of ex situ Kelvin probe force microscopy together with Raman spectroscopy and atomic force microscopy. The amount of residual strain induced is calculated to between 1.3% and 0.7%. Results also show that the magnitude of strain increased with growth time while the uniformity of strain improved.

Mechanisms of epitaxial growth of SiC films by the method of atom substitution on the surfaces (100) and (111) of Si single crystals and on surfaces of Si films grown on single crystals Al2O3

The structure and morphology of silicon carbide (SiC) films formed by a new method of atom substitution on the surfaces (100) and (111) of silicon substrates (Si) were investigated. It is shown that the singular faces (100) of Si in the process of substitution of silicon atoms for carbon atoms are transformed into a face of SiC, consisting of an ensemble of facets resembling saw-tooth structures, the side surfaces of which are covered with planes (111) and (110) and (210). Theoretically, a fundamentally different mechanism of atom substitution on the faces (111) and faces (100) is described and experimentally confirmed. It was found that on the vicinal surface of Si, deviated 4° or more from the singular face (100), during the synthesis of SiC, an ordered phase of SiC is formed, the surface morphology of which appears as of facets (scales) consisting of faces (111). It is shown that the method of topochemical substitution of atoms can grow epitaxial SiC layers not only on a silicon substrate, but also on substrates of other materials, in particular, on single-crystal sapphire substrates.

Spin transport in epitaxial graphene on the C-terminated (0001¯)-face of silicon carbide

We performed a temperature dependent study of the charge and spin transport properties of epitaxial graphene on the C-terminated (0001¯) face of silicon carbide (SiC), a system without a carbon buffer layer between the graphene and the SiC. Using spin Hanle precession in the nonlocal geometry, we measured a spin relaxation length of λS = 0.7 μm at room temperature, lower than in exfoliated graphene. We show that the charge and spin diffusion coefficient, DC and DS, respectively, increasingly deviate from each other during electrical measurements up to a difference of a factor 4. Thus, we show that a model of localized states that was previously used to explain DC ≠ DS, can also be applied to epitaxial graphene systems without a carbon buffer layer. We attribute the effect to charge trap states in the interface between the graphene and the SiC.

Initial stage of the epitaxial assembly of graphene from silicon carbide and its simulation by semiemprical quantum chemical methods: Carbon face

The epitaxial growth of graphene on a singular carbon face of silicon carbide is simulated by semiempirical quantum chemical methods. It is shown that the main regularities of the growth of graphene on such a face, i.e., the sequence of surface reconstructions with a short spatial period (2 × 2) → (3 × 3) → graphene, are exhibited naturally during the analysis of various paths of graphene assembly and seeking the most probable path.

Insights into few-layer epitaxial graphene growth on4H-SiC(0001¯)substrates from STM studies

Epitaxial carbon was grown by heating $(000\overline{1})$ silicon carbide (SiC) to high temperatures $(1450--1600\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C})$ in vacuum. A continuous graphene surface layer was formed at temperatures above $1475\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$. X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) were extensively used to characterize the quality of the few-layer graphene (FLG) surface. The XPS studies were useful in confirming the graphitic composition and measuring the thickness of the FLG samples. STM studies revealed a wide variety of nanometer-scale features that include sharp carbon-rich ridges, moir\'e superlattices, one-dimensional line defects, and grain boundaries. By imaging these features with atomic-scale resolution, considerable insight into the growth mechanisms of FLG on the carbon face of SiC is obtained.

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).

The Influence of Surface Preparation on the Properties of SiC on Si(111)

The silicon (111) surface was converted into silicon carbide by using: 1. propane diluted in hydrogen and rapid thermal processing, 2. elemental carbon deposited onto the silicon surface by solid source molecular beam epitaxy and subsequent annealing, i.e. conversion in a hydrogen poor environment, 3. modification of the silicon surface by Ge predeposition prior to elemental carbon deposition. These methods were compared according to their influence on the structure, morphology and electronic properties of the SiC/Si(111) heteroepitaxial system. It was found that the conversion in a hydrogen rich environment leads to the formation of a carbon () silicon carbide face, whereas a silicon (111) silicon carbide face was formed under hydrogen poor conditions. Germanium predeposition led to an improvement of the structural morphological and electrical properties of the silicon carbide–silicon heteroepitaxial system.

Effect of oxidation method and post-oxidation annealing on interface properties of metal–oxide–semiconductor structures formed on n-type 4H-SiC C(0001̄) face

The C(0001̄) face of silicon carbide (SiC) has superior properties such as a faster oxidation ratio and a smoother surface compared with the Si(0001) face. We have investigated the oxidation and post-oxidation annealing effects on the capacitance–voltage and the interface state density (Dit) of n-type SiC metal–oxide–semiconductor (MOS) structures formed on the C(0001̄) face. It was found that pyrogenic oxidation and hydrogen annealing above 700 °C reduced Dit near the conduction-band edge. The value of Dit at Ec−E=0.2 eV is 1×1012 eV−1 cm−2, which is comparable with that of the MOS structure formed on the Si(0001) face. However, the value of Dit around the deep level at Ec−E=0.6 eV is one order of magnitude higher than that of n-type MOS structures formed on the Si(0001) face. It is very important to reduce Dit at the deep level for a high-quality SiO2/SiC interface on the 4H-SiC C(0001̄) face.

Formation of brittle phases at the boron fiber and boron with barrier coatings fiber-molten aluminum interphase boundary

This article investigates the structure and phase composition of the products of the reaction at the molten aluminium-boron fiber interface. The reaction product consists chiefly of aluminium boride. The results of x-ray diffraction and a series of mechanical tests are given as well as the behavior of the constituents in the face of silicon carbide and boron carbide coatings on the fibers.