Materials Science Forum Vols. 740-742

Abstract: The unique quantum properties of the nitrogen–vacancy (NV) center in diamond have motivated efforts to find defects with similar properties in silicon carbide (SiC), which can extend the functionality of such systems not available to the diamond. As an example, results of experiments on electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) are presented suggests that silicon vacancy (VSi) related point defects in SiC possess properties the similar to those of the NV center in diamond, which in turn make them a promising quantum system for single-defect and single-photon spectroscopy in the infrared region. Depending on the defect type, temperature, SiC polytype, and crystalline position, two opposite schemes have been observed for the optical alignment of the high-spin ground state spin sublevels population of the VSi-related defects upon irradiation with unpolorized light. Spin ensemble of VSi-related defects are shown to be prepared in a coherent superposition of the spin states even at room temperature. Zero-field (ZF) ODMR shows the possibility to manipulate of the ground state spin population by applying radiofrequency field. These altogether make VSi-related defects in SiC very favorable candidate for spintronics, quantum information processing, and magnetometry.

Abstract: The effects of carbon content on the piezoresistive properties of non-stoichiometric silicon carbide (SixCy) films deposited on thermally oxidized (100) Si substrates by Plasma Enhanced Chemical Vapor Deposition (PECVD) from silane (SiH4) and methane (CH4) gas mixtures have been investigated. Four different film compositions have been obtained by varying SiH4 flow ratios from 1.0 to 4.0 sccm, while the other parameters were kept constant. In order to evaluate the piezoresistive properties of the SixCy films, we have developed test structures consisting of SixCy thin-film resistors defined by reactive ion etching (RIE) with Ti/Au pads formed by lift-off process. The gauge factor (GF) and temperature coefficient of resistance (TCR) of each SixCy film were measured.

Abstract: Plasma-assisted polishing (PAP) was proposed for finishing difficult-to-machine materials, such as single-crystal SiC, reaction-sintered SiC, diamond, and sapphire. In the case of PAP application to the finishing of the 4H-SiC surface, an atomically smooth surface without any scratches was obtained. In this study, we observed 4H-SiC (0001) surfaces processed by water vapor plasma oxidation and PAP using ceria abrasives through cross-sectional transmission electron microscopy (XTEM). Water vapor plasma oxidation was conducted for 1 min, 5 min and 60 min. An intermediate layer located between SiO2 and SiC, which corresponds to silicon oxycarbide, was clearly observed in the case of a short oxidation. As oxidation time increased from 1 min to 60 min, average oxidation rate decreased from 2.7 nm/min to 0.6 nm/min. An atomically smooth 4H-SiC (0001) surface was obtained after PAP for 60 min using ceria abrasives.

Abstract: The nitrogen donors residing at quasi-cubic lattice site (N_k) in 4H SiC were investigated by field sweep electron spin echo (FS ESE), pulsed electron nuclear double resonance (ENDOR) and pulsed General TRIPLE ENDOR spectroscopy. The ²⁹Si and ¹³C superhyperfine lines observed in the FS ESE and ENDOR spectra of N_k in n-type 6H SiC were assigned by pulsed General TRIPLE resonance spectroscopy to the specific carbon (C) and silicon (Si) atoms located in the nearest environment of N_k in 4H SiC. The superhyperfine interaction constants and their relative signs for Nk with ²⁹Si and ¹³C nuclei located in the nearest-neighbor shells are found from the General TRIPLE ENDOR spectra to be positive for C atoms and negative for Si atoms.

Abstract: A series of 4H-SiC bulk wafers with different carrier concentrations were studied by Raman scattering in temperature range of 80K to 873K. Different Raman phonon modes of 4H-SiC can be clearly observed. Most Raman peaks of different modes shift to lower frequency with increasing temperature. But abnormal behavior can be observed in the longitudinal optical-plasma coupling mode, which does not decrease in frequency monotonously when temperature increases like other Raman modes. It increases at relatively low temperature and begins to drop after a critical temperature.

Abstract: The purpose of the present study is to study the crystal periodicities that appear in 4H- and 6H-SiC material after the implantation with nitrogen and prior to post-implantation annealing. High Resolution X-Ray diffraction (HRXRD) and Transmission Electron Microscopy (TEM) have been employed towards this purpose. Extra peaks at smaller, than the main (00n) peak, diffraction angles in HRXRD scans and extra spots in the electron diffraction patterns have been observed due to the presence of these periodicities. Higher lattice constant periodic structures are apparently formed from the implanted nitrogen ions located at interstitial sites and disappear after the annealing and the resulting positioning of nitrogen atoms in substitutional sites.

Abstract: It has been widely accepted that wide-band-gap semiconductor SiC can provide low-loss semiconductor switches and diodes for the power electronics applications. The SiC devices enable the low-loss and compact converters and inverters.

Abstract: We investigated the atomistic mechanism of N incorporation during SiC oxidation by the first principles calculation. We found that N atoms play two characteristic roles in NO oxidation of SiC surface. One is that N atoms tend to form three-fold coordinated covalent bonds on a SiC(0001) surface, which assist the termination of surface dangling bonds, leading to improve the interface properties. The other is that N atoms form N-N bond like a double bond. The N2 molecule is desorbed from SiC surface, which do not disturb the oxidation process of SiC surfaces. These results indicate that N incorporation is effective to suppress defect state generation at SiO2/SiC interfaces during SiC oxidation.

Abstract: A NH/3C-SiC heterojunction and a heterostructur of the NH/3C/NH type (N = 2, 4, 6, 8) are consid-ered. Two possibilities are analyzed for heterojunctions, in which a Si or a C is the contact plane of the NH polytype. In this case, the energies of the quasi-local levels in the quantum wells at the interface will be different. With the difference of these energies measured, it is possible to determine the spon-taneous polarization inherent in the NH polytype. In the presence of a spontaneous polarization field, the quasi-local levels in the left- and right-hand quantum wells of the heterostructure have dif-ferent energies. It is shown that, if the heterostructur is placed in an external electric field, it is possible to determine the magnitude of the spontaneous polarization by calculating the different between the energies of these levels. Experimental ways to find by using the suggested theoretical scenario are discussed.

Abstract: This paper aims to establish a new method to characterize the interface between 4H-SiC and passivating dielectric layers. The investigations are made on MOS test structures utilizing Al₂O₃ and SiO₂ dielectrics on 4H-SiC. These devices are then exposed to various fluences of Ar⁺ implantation and then measured by the new method utilizing optical free carrier absorption (FCA) technique to assess the interface traps. A program has been developed using MATLAB to extract surface recombination velocity (SRV) at the oxide/epi-layer interface from the optical data. Capacitance-voltage (CV) is done to extract the density of interface traps (D_it) and a comparison was made. It is observed that SiO₂ samples show a large rise of SRVs, from 0.5×10⁴ cm/s for a reference sample to 8×10⁴ cm/s for a fluence of 1×10^₁₂ cm^-2, whereas Al₂O₃ samples show more stable SRV, changing from 3×10⁴ cm/s for the un-irradiated reference sample to 6×10⁴ cm/s for a fluence of 1×10¹² cm^-2. A very similar trend is observed for D_it values extracted from CV measurements and it can therefore be concluded that the FCA method is a suitable technique for the interface characterization.