Franziska Christine Beyer

Deep levels in iron doped n- and p-type 4H-SiC

Deep levels were detected in Fe-doped n- and p-type 4H-SiC using deep level transient spectroscopy (DLTS). One defect level (EC 0.39 eV) was detected in n-type material. DLTS spectra of p-type 4H-S ...

Deep levels in tungsten doped n-type 3C–SiC

Tungsten was incorporated in SiC and W related defects were investigated using deep level transient spectroscopy. In agreement with literature, two levels related to W were detected in 4H–SiC, whereas only the deeper level was observed in 6H–SiC. The predicted energy level for W in 3C–SiC was observed (EC−0.47 eV). Tungsten serves as a common reference level in SiC. The detected intrinsic levels align as well: E1 (EC−0.57 eV) in 3C–SiC is proposed to have the same origin, likely VC, as EH6/7 in 4H–SiC and E7 in 6H–SiC, respectively.

Defects in 4H-SiC Layers Grown by Chloride-based Epitaxy

Chloride-based 4H-SiC epitaxial layers were investigated by DLTS, MCTS and PL. The DLTS spectra of the as grown samples showed dominance of the Z1/2 and the EH6/7 peaks. For growth rates exceeding 100 µm/h, an additional peak occurred in the DLTS spectra which can be assigned to the UT1 defect. The shallow and the deep boron complexes as well as the HS1 defect are observed in MCTS measurements. The PL spectra are completely dominated by the near band gap (NBG) emission. No luminescence from donor-acceptor pair occurred. The PL line related to the D1 centre was weakly observed. In the NBG region nitrogen bound exciton (N-BE) and free exciton (FE) related lines could be seen. The addition of chlorine in the growth process gives the advantage of high growth rates without the introduction of additional defects.

Chloride-Based CVD at High Rates of 4H-SiC on On-Axis Si-Face Substrates

The epitaxial growth at 100 µm/h on on-axis 4H-SiC substrates is demonstrated in this study. Chloride-based CVD, which has been shown to be a reliable process to grow SiC epitaxial layers at rates above 100 µm/h on off-cut substrates, was combined with silane in-situ etching. A proper tuning of C/Si and Cl/Si ratios and the combination of different chlorinated precursors resulted in the homoepitaxial growth of 4H-SiC on Si-face substrates at high rates. Methyltrichlorosilane, added with silane, ethylene and hydrogen chloride were employed as precursors to perform epitaxial growths resulting in very low background doping concentration and high quality material, which could be employed for power devices structure on basal-plane-dislocation-free epitaxial layers.

Observation of Bistable Defects in Electron Irradiated N-Type 4H-SiC

DLTS measurements show bistable behavior of the previously reported EH5 peak in low- and high-energy electron irradiation 4H-SiC. Both reconfiguration processes (A ! B and B ! A) take place above 700 ±C. By isothermal annealing, the reconfiguration rates were determined and the reconfiguration energy was calculated to EA = 2.4±0.2 eV. Since the defect is present already after low-energy electron irradiation, which mainly affects the C atom in SiC, the EH5 peak may be related to defects associated with C-vacancies or C-interstitials

Annealing behavior of the EB-centers and M-center in low-energy electron irradiated n-type 4H-SiC

After low-energy electron irradiation of epitaxial n-type 4H-SiC with a dose of 5×1016 cm−2, the bistable M-center, previously reported in high-energy proton implanted 4H-SiC, is detected in the deep level transient spectroscopy (DLTS) spectrum. The annealing behavior of the M-center is confirmed, and an enhanced recombination process is suggested. The annihilation process is coincidental with the evolvement of the bistable EB-centers in the low temperature range of the DLTS spectrum. The annealing energy of the M-center is similar to the generation energy of the EB-centers, thus partial transformation of the M-center to the EB-centers is suggested. The EB-centers completely disappeared after annealing temperatures higher than 700 ∘C without the formation of new defects in the observed DLTS scanning range. The threshold energy for moving Si atom in SiC is higher than the applied irradiation energy, and the annihilation temperatures are relatively low, therefore the M-center, EH1 and EH3, as well as the EB...

Deep levels in hetero‐epitaxial as‐grown 3C‐SiC

3C‐SiC grown hetero‐epitaxially on 4H‐ or 6H‐SiC using a standard or a chloride‐based CVD process were electrically characterized using IV, CV and DLTS. The reverse leakage current of the Au‐Schottky diodes was reduced to lower than 10−8 A at −2V by a thermal oxidation step using UV‐light illumination at 200° C. The Schottky barrier height of the Ni and Au contacts were determined by IV measurement to be φB = 0.575 eV and φB = 0.593 eV, respectively, for a contact diameter of about 150 μm. One dominant DLTS peak was observed in the 3C‐epilayers independently of the substrate at about EC−0.60 eV which is attributed to W6‐level in 3C‐SiC. This deep level is thought to be related to an intrinsic defect.

Very High Growth Rate of 4H-SiC Using MTS as Chloride-Based Precursor

The chlorinated precursor methyltrichlorosilane (MTS), CH3SiCl3, has been used to grow epitaxial layers of 4H-SiC in a hot wall CVD reactor, with growth rates as high as 170 µm/h at 1600°C. Since MTS contains both silicon and carbon, with the C/Si ratio 1, MTS was used both as single precursor and mixed with silane or ethylene to study the effect of the C/Si and Cl/Si ratios on growth rate and doping of the epitaxial layers. When using only MTS as precursor, the growth rate showed a linear dependence on the MTS molar fraction in the reactor up to about 100 µm/h. The growth rate dropped for C/Si < 1 but was constant for C/Si > 1. Further, the growth rate decreased with lower Cl/Si ratio.

Defects in low-energy electron-irradiated n-type 4H-SiC

The bistable M-center, previously observed in high-energy proton-implanted 4H-SiC, was detected in low-energy electron-irradiated 4H-SiC using deep-level transient spectroscopy (DLTS). Irradiation ...

Chloride-based SiC Epitaxial Growth

Some aspects of the chloride-based CVD growth process have been investigated by using both the approach to add HCl to the standard precursors or/and by using the single molecule precursor methyltrichlorosilane (MTS). The efficiency of the process for different precursors, the growth rate stability and the effect that the Cl/Si-ratio has on the growth have been studied. MTS is showed to be the most efficient precursor; the growth can be hindered by to much chlorine in the gas mixture. The Cl/Si-ratio is also found to be a process parameter that affects the amount of incorporated nitrogen in the epilayers.