Surface Of 4H Research Articles

Electron Diffraction Study of Epitaxial Graphene Structure Grown upon SiC (0001) Thermal Destruction in Ar Atmosphere and in High Vacuum

We have studied the structure of epitaxial graphene obtained as a result of thermal desorption of the silicon carbide surface under conditions of vacuum synthesis and in Ar medium by reflection electron diffraction. As a result of the study, a significantly more uniform buffer layer coating of the SiC surface by epitaxial graphene has been found when forming in inert medium on the surface of 4H- and 6H-SiC(0001) polytypes compared with the synthesis of graphene in high vacuum. The quality of the coating has been shown to depend on the degree of perfection of the original single crystal.

Activation and control of visible single defects in 4H-, 6H-, and 3C-SiC by oxidation

In this work, we present the creation and characterisation of single photon emitters at the surface of 4H- and 6H-SiC, and of 3C-SiC epitaxially grown on silicon. These emitters can be created by annealing in an oxygen atmosphere at temperatures above 550 °C. By using standard confocal microscopy techniques, we find characteristic spectral signatures in the visible region. The excited state lifetimes are found to be in the nanosecond regime in all three polytypes, and the emission dipoles are aligned with the lattice. HF-etching is shown to effectively annihilate the defects and to restore an optically clean surface. The defects described in this work have ideal characteristics for broadband single photon generation in the visible spectral region at room temperature and for integration into nanophotonic devices.

Polytype Stability and Microstructural Characterization of Silicon Carbide Epitaxial Films Grown on [ $$ {\hbox{11}}\overline{{\hbox{2}}} {\hbox{0}} $$ ]- and [0001]-Oriented Silicon Carbide Substrates

The polytype and surface and defect microstructure of epitaxial layers grown on 4H( $$ {\hbox{11}}\overline{{\hbox{2}}} {\hbox{0}} $$ ), 4H(0001) on-axis, 4H(0001) 8° off-axis, and 6H(0001) on-axis substrates have been investigated. High-resolution x-ray diffraction (XRD) revealed the epitaxial layers on 4H( $$ {\hbox{11}}\overline{{\hbox{2}}} {\hbox{0}} $$ ) and 4H(0001) 8° off-axis to have the 4H-SiC (silicon carbide) polytype, while the 3C-SiC polytype was identified for epitaxial layers on 4H(0001) and 6H(0001) on-axis substrates. Cathodoluminescence (CL), Raman spectroscopy, and transmission electron microscopy (TEM) confirmed these results. The epitaxial surface of 4H( $$ {\hbox{11}}\overline{{\hbox{2}}} {\hbox{0}} $$ ) films was specular with a roughness of 0.16-nm root-mean-square (RMS), in contrast to the surfaces of the other epitaxial layer-substrate orientations, which contained curvilinear boundaries, growth pits (∼3 × 104 cm−2), triangular defects >100 μm, and significant step bunching. Molten KOH etching revealed large defect densities within 4H( $$ {\hbox{11}}\overline{{\hbox{2}}} {\hbox{0}} $$ ) films that decreased with film thickness to ∼106 cm−2 at 2.5 μm, while cross-sectional TEM studies showed areas free of defects and an indistinguishable film-substrate interface for 4H( $$ {\hbox{11}}\overline{{\hbox{2}}} {\hbox{0}} $$ ) epitaxial layers.

Strong dispersion of the surface optical phonon of silicon carbide in the near vicinity of the surface Brillouin zone center

The surface optical or Fuchs–Kliewer phonons of the (0 0 1) surface of 3C-SiC and the Si-terminated (0 0 0 1) surfaces of 4H- and 6H-SiC have been investigated with high resolution electron energy loss spectroscopy (HREELS). For each of the SiC polytypes the frequency of the surface optical phonon changes with surface reconstruction, indicating subtle differences in the static polarization at differently reconstructed surfaces. Due to their anisotropy, hexagonal surfaces exhibit a second, much weaker Fuchs–Kliewer mode. For all surfaces under examination, a linear dispersion of the Fuchs–Kliewer mode frequency has been found for wave vectors close to the Γ ¯ -point. This dispersion can be explained by dynamical dipole coupling between atomic oscillators at the surface of the highly polar silicon carbide.

Functional surface reconstructions of hexagonal SiC

The basal surfaces of hexagonal SiC exhibit a large variety of surface reconstructions thatdevelop under a similarly rich variety of sample preparations. A subset of these surface phases,which have been investigated in structural detail using scanning tunnelling microscopy andquantitative low-energy electron diffraction, is described and shown to offer the scope to beused for the formation of SiC-based semiconductor devices. The phases discussed are the(3 × 3) and reconstructions for the (0001) surfaces of 4H- and 6H-SiC and the oxygen-uptake-driven reconstructions of these polytypes for both the (0001) and the (000) surface orientations. We show that the(3 × 3) reconstruction corresponds to a highly passivated surface that facilitates hexagonalsingle-crystal growth, while suitable preparation of the reconstruction favours a switch to cubic growth and hence to the formation of aheterojunction. The reconstructions promise to form defect-free interfaces to insulating silicon oxide films,which is important for device applications.

STUDIES OF $4{\rm H}\mbox{--}{\rm SiC}(0001){\rm Si}(\sqrt3\times\sqrt3)$ AND (0001)C(3×3) SURFACES AND THEIR METALLIZATION PROCESS BY NI USING STM, AES AND LEED

Several methods have been tried to prepare clean surfaces of 4H–SiC(0001)Si and C, whose surface atomic, or electronic, structures have been studied by LEED (low energy electron diffraction) STM (scanning tunneling microscopy) and AES (Auger electron spectroscopy). Some sequential chemical treatments, for example, agitation in an organic solvent and dipping in HF solution, followed by the heating of a SiC wafer in UHV (ultrahigh vacuum, below 10-7 Pa) at 950°C, gave either a [Formula: see text] or 3×3 superstructure, observed by LEED (low energy electron diffraction), for the SiC(0001) Si or C surface, respectively. An elongated NH4F treatment followed by a heat treatment in UHV at ~950°C gave a rather flat region to be investigated by STM, where a [Formula: see text] superstructure for the SiC(0001) Si surface has been observed. In the case of metal (Ni) atom deposition on SiC(0001) [Formula: see text] and (0001)C(3×3) surfaces, AES and LEED analysis have clarified that deposited metal atoms form islands up to ~5 Å. However, Ni atoms dispersed uniformly at the very beginning of the deposition, which means that the Ni overlayer piles up in layer followed by island growth mode.

Silicate Monolayers on the Hexagonal Surfaces of 4H- and 6H-SiC

Silicate Monolayers on the Hexagonal Surfaces of 4H- and 6H-SiC

Stepped morphology on 4H and 15R silicon carbide: modelling by a random walk

A random walk algorithm for modelling the development of stepped morphology in a diffusion mediated step flow growth is applied to the {0001} surface of 4H (hexagonal) and 15R (rhombic) polytype modifications of silicon carbide grown by vapour phase epitaxy. The algorithm includes variable desorption of adatoms from terraces as well as their variable accommodation at steps. By using this algorithm it is shown that characteristic step heights of 4 and 5 ML often observed on the surface of 4H and 15R SiC are the result of a specific stacking sequence in the [0001] direction. A change between ABC and ACB stacking order implies two kinds of adatom accommodation kinetics (fast and slow) at steps in any of the 〈11̄00〉 directions in the {0001} plane which originate from the different number of dangling bonds at the step edge in ABC and ACB stacked layers. Therefore during the growth fast steps can take over, occupy positions at the top of the step riser and dominate in controlling the growth rate. The results of the simulation show that 4 and 5 ML step heights as well as step bunching are intrinsic properties of the crystal structure and of its kinetical parameters.