GaN epitaxial growth on 4 degree off-axis Si- and C-face 4H-SiC without buffer layers by tri-halide vapor-phase epitaxy with high-speed wafer rotation

The results of GaN epitaxial crystal growth on 4° off-axis Si- and C-face 4H-SiC without buffer layers by tri-halide vapor-phase epitaxy (THVPE) with high-speed wafer rotation and the properties of the obtained material are briefly described in this paper. GaN epitaxial layers were grown on 4° off-axis 4H-SiC(0001)Si and 4H-SiC(000-1)C substrates. The obtained material's properties were studied by Nomarski optical microscopy, scanning electron microscopy, photoluminescence, surface two-photon excitation microscopy, X-ray diffraction and Raman spectroscopy. The structural and optical properties of the GaN epitaxial layer are presented and discussed. By adopting an external GaCl3 material supply system, high-speed rotation was applicable, and its effect was confirmed. The results show that when THVPE was used under growth pressure of 600 mbar at 900 °C–950 °C, the surface reaction rate was sufficiently high, and the GaN epitaxial layer was grown under conditions of controlled raw-material supply rates. High growth rates (40–50 μm h−1) and relatively low threading dislocations (~7 × 107 cm−2) were achieved on 4° off 4H-SiC(000-1)C despite the large lattice mismatch (3.1%) between SiC and GaN and without any buffer layers by introducing step flow growth and growth on a high-quality 4H-SiC substrate. We found that epitaxial layers with a smooth surface morphology can be grown on 4H-SiC(000-1)C compared with growth on 4H-SiC(0001)Si.

Source:IOPscience
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Electronic structures and magnetic properties of (Al, Cr) co-doped 4H-SiC: a first-principles study

Electronic and magnetic properties of Cr-doped 4H silicon carbide (4H-SiC) with Al and silicon vacancies (V Si) are studied by first principles calculations. Our results indicate that the (Cr, V Si)-codoped 4H-SiC favours ferromagnetic (FM) ground state, which is enhanced by the nearest-neighboring V Si while is weakened at other positions. For (Cr, Al)-codoped 4H-SiC system, all configurations are ferromagnetic ground state and the stability is greatly enhanced. It is found that indirect ferromagnetic coupling between Cr cations through the hybridization between Cr:3d and Si:3p, C:2p orbitals leads to a Cr1:3d-C:2p-Cr2:3d coupling chain. We also investigated silicon vacancy induced in (Cr, Al)-codoped 4H-SiC system, the results indicate that all configurations are antiferromagnetic states. Our research gives an effective method to investigate the ferromagnetism materials' doping effect, which benefits for the design of 4H-SiC dilute magnetic semiconductors in magnetism materials.

Source:IOPscience
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Evaluation of nitrogen incorporation into bulk 4H-SiC grown on seeds of different orientation from optical absorption spectra

The effectiveness of n-type nitrogen doping of bulk 4H-SiC grown on seeds of different orientation is studied by optical absorption measurements. The 4H-SiC ingots have been grown by physical vapour transport (PVT), with nitrogen doping from the SiC source. The nitrogen concentration was determined at room temperature from the absorption peak intensity at 464 nm, with account for the degree of donor ionization. It has been shown that 4H-SiC ingots grown on Si (11-22) faces are significantly less doped by nitrogen than the ones grown on C (11-2-2).

Source:IOPscience
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Ti/4H-SiC Schottky diode breakdown voltage with different thickness of 4H-SiC epitaxial layer

Breakdown voltage for Ti/4H-SiC type Schottky diode with six guard rings have been calculated theoretically and by mean of numerical simulations. It is shown that the breakdown voltage can be increase at the minimum on 100 V in case when thickness of the n-type 4H-SiC epitaxial layer increase from 18 up to 22 μm. It is established that the breakdown voltage value for Ti/4H-SiC type Schottky diode with guard rings calculated by mean simulation in ATLAS program and theoretically have good approximation. Thus, above approach gives the possibility for projection of diode structure with different 4H-SiC epitaxial layer thickness with higher breakdown voltage value.

Source:IOPscience
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