Magnetic Structure of Mn-doped 6H-SiC

We investigated the local magnetic properties of Mn-doped 6H-SiC using ab-initio calculations. The calculation addresses various configurations of Mn single impurity and Mn dimers at substitutional/interstitial sites with and without neighboring Si and C vacancies. The calculations showed that a substitutional Mn atom at either Si or C sites possesses a magnetic moment. The Mn atom at Si site possesses larger magnetic moment than Mn atom at C site. Our calculations show that antiferromagnetically coupled pair of Mn atoms at Si sites with neighboring C vacancy is magnetically more stable. The calculation also showed that the interstitial sites with C neighbors are more favorable than those with Si and the magnetic moment for Mn at interstitial sites is less compared to that at substitutional sites. The results are used to understand the experimental data obtained on Mn- 6H-SiC for various Mn concentrations.

Source:IOPscience

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β-FeSi2 films prepared on 6H-SiC substrates by magnetron sputtering

β-FeSi2 thin films have been successfully prepared by magnetron sputtering and post rapid thermal annealing method on 6H-SiC (0001) substrates using a FeSi2 target and a Si target. X-ray diffraction (XRD) and Raman spectroscopy are applied to analyze the formation of β-FeSi2 films. XRD spectra reveal that the amorphous FeSi2 films are transformed to β-FeSi2 phase as the annealing temperature is increased from 500 to 900 °C for 5 min and the optimal annealing temperature is 900 °C. The formation of β-FeSi2 is also confirmed by Raman spectroscopy. Scanning electron microscope (SEM) observations indicate that the film is flat, relatively compact and the interface between β-FeSi2 and 6H-SiC is clear. Atomic force microscope (AFM) measurements demonstrate that the surface roughness confirmed by the root mean square (RMS) of the β-FeSi2 film is 0.87 nm. Near-infrared spectrophotometer observation shows that the absorption coefficient is of the order of 105 cm−1 and the optical band-gap of the β-FeSi2 film is 0.88 eV. The β-FeSi2 film with high crystal quality is fabricated by co-sputtering a FeSi2 target and a Si target for 60 min and annealing at 900 °C for 5 min.

Source:IOPscience

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Electron beam processing of 6H-SiC substrate to obtain graphene-like carbon films

We report on growth of graphene-like carbon films on 6H-SiC {0001} substrate by electron-beam. The processing was carried out on a specialized electron beam system with the Pierce electron gun. The D, G, and 2D peaks as well as D/G (0.2-0.9) and 2D/G (0.7-0.9) ratios are detected on processed samples by Raman spectroscopy. The prominent bands D, G, and 2D are located at 1350, 1584, and 2707 cm−1, respectively. Atomic force microscopy showed that the average roughness lies in the range from 5 to 30 nm, and ten point height – from 40 to 200 nm. The results demonstrate that the electron-beam technique is appropriate to form graphene-like structures directly on 6H-SiC substrates and could be used for electronic device fabrication.

Source:IOPscience

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Chemical Vapor Cleaning of 6H‐SiC Surfaces

The techniques (temperature range of study) of in situ thermal desorption (500‐1100°C) and chemical vapor cleaning (CVC) via exposure to  and/or  (750‐1100°C) have been investigated for preparing  surfaces suitable for epitaxial growth of SiC and III‐nitride films, and are compared with regard to surface purity, stoichiometry, and structural order. Oxide removal below the detection limits of Auger electron spectroscopy was achieved for all orientations via annealing in  at 850‐900°C or ≈200° lower than necessary by thermal desorption. No non‐SiC carbon was detected on the surface by X‐ray photoelectron spectroscopy. An approximately one‐tenth of a monolayer of oxygen coverage and significant quantities of non‐SiC carbon were detected for all 6H‐SiC surfaces prepared by thermal desorption. In contrast to the predominantly non‐SiC carbon‐rich surfaces prepared by thermal desorption, the stoichiometry of the SiC surfaces prepared by CVC could be manipulated from Si‐rich to C‐rich without non‐SiC carbon formation by either extending the  exposures or by following with  exposure. The latter surfaces also had lower concentrations of both oxygen and non‐SiC carbon and increased surface order. © 1999 The Electrochemical Society. All rights reserved.

Source:IOPscience

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Fibrous and Porous Microstructure Formation in 6H‐SiC by Anodization in HF Solution

The anodization reaction of 6H‐SiC using a HF solution was investigated to understand the formation of porous SiC. The anodization reaction proceeds via two stages in which the oxidation of SiC is followed by the removal of SiO by fluorine ions. The microstructure of porous SiC changes from fibrous to dendritic as the anodization current is increased, and also shows other transitional morphology. The photoluminescence of these porous SiC with different microstructures was also investigated, and the photoluminescence band of higher energy was found to become enhanced as the microstructure of porous SiC changed from fibrous to porous dendritic.

Source:IOPscience

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Design and Performance of a New Reactor for Vapor Phase Epitaxy of 3C, 6H, and 4H SiC

The design of a new horizontal reactor for vapor phase epitaxy of SiC is presented. The reactor has a graphite inner cell with rectangular cross section to align the gas stream, and it may handle temperatures up to 1700°C. The inner cell is surrounded by a highly reflecting heat shield. 6H and 4H SiC were grown homoepitaxially, and 3C SiC was grown on (111) and (001) oriented Si. The 3C SiC is shown to be epitaxially oriented to the substrate, but with some mosaicity. For 4H and 6H SiC the crystallinity is limited by the substrates, and for layers thicker than 20 μm step bunching appears. Unintentionally doped material is n‐type and has a doping concentration in the 1015 cm−3 range. Intentional N and Al doping could be controlled from 1016 cm−3 up to 1019 and 1021 cm−3, respectively. The compensation level is in all cases in the range of 1014 cm−3. The Al doping turn‐off from a concentration of  to  over 50 nm has been achieved by using an HCl etch at the interface. The thickness uniformity is within ±24% for growth at 1250°C, but improved to within ±6% for growth at 1550°C. From growth behavior at different growth conditions we conclude that the process is mainly diffusion limited.

Source:IOPscience

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A comparative DFT study of electronic properties of 2H-, 4H- and 6H-SiC(0001) and SiC(000 \bar{1} ) clean surfaces: significance of the surface Stark effect

The electric field, uniform within a slab, emerging due to Fermi level pinning at both sides of the slab, is analyzed using DFT simulations of SiC surface slabs of different thicknesses. It is shown that for thicker slabs the field is nonuniform and this fact is related to the surface state charge. Using the electron density and potential profiles, it is proved that for high-precision simulations it is necessary to take into account a sufficient number of SiC layers. We show that the use of 12 diatomic layers leads to satisfactory results. It is also demonstrated that the change of the opposite side slab termination, both by different types of atoms or by their location, can be used to adjust the electric field within the slab, creating a tool for simulation of surface properties, depending on the doping in the bulk of the semiconductor. Using these simulations, it was found that, depending on the electric field, the energy of the surface states changes in a different way than the energy of the bulk states. This criterion can be used to distinguish Shockley and Tamm surface states. The electronic properties, i.e. energy and type of surface states of the three clean surfaces: 2H-, 4H-, 6H-SiC(0001) and SiC(), are analyzed and compared using field-dependent DFT simulations.

Source:IOPscience

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