Materials Science Forum Vols. 740-742

Abstract: 3C-SiC is the only polytype that grows heteroepitaxially on Si substrates and, therefore, it is of high interest for various potentail applications. However, the large (~20 %) lattice mismatch of SiC with the Si substrate causes a serious problem. In this respect, rotated epitaxy of 3C-SiC(111) on the Si(110) substrate is highly promising because it allows reduction of the lattice mismatch down to a few percent. We have systematically searched the growth conditions for the onset of this rotated epitaxy, and have found that the rotaed epitaxy occurrs at higher growth temperatures and at lower source-gas pressures. This result indicates that the rotated epitaxy occurs under growth conditions that are close to the equilibrium and is thefore thermodynamically, rather than kinetically, driven.

Abstract: 8H-SiC epilayers grown on small 8H-SiC Lely platelets are investigated optically using photoluminescence spectroscopy. At low temperature the near band gap emission detected in the 2.78 to 2.67 eV range contains sharp lines associated to nitrogen-bound-exciton recombination. Three different no-phonon lines are detected accompanied by their phonon replicas. Free-exciton replicas are also observed which allows the determination of the excitonic band gap. The binding energy of the bound excitons can thus be determined and the ionization energies of the three nitrogen levels in 8H-SiC are estimated and found to be rather shallow compared to the values for other hexagonal polytypes. Additional bound-exciton lines are observed when the experimental photoluminescence temperature is increased.

Abstract: Carrier removal rate (Vd) in p-6H-SiC in its irradiation with 8 MeV protons has been studied. p-6H-SiC samples were produced by sublimation in a vacuum. Vd was determined by analysis of capacitance-voltage characteristics and from results of Hall effect measurements. It was found that full compensation of samples with initial value of Na-Nd 1.5 x1018 cm-3 occurs at an irradiation dose of ~1.1 1016 cm-2. In this case, the carrier removal rate was ~130 cm-1

Abstract: Raman scattering spectra have been collected on p-type 4H-SiC samples doped with aluminum up to 5×10¹⁹ atoms per cubic cm. The distortion and asymmetry of FTA modes which appear in the low frequency range has been probed in great details. We show that, using standard Fano formulae with three parameters per mode, one can successively fit all FTA modes profiles in the concentration range 2×10¹⁶ – 5×10¹⁹ Al.cm^-3.

Abstract: EPR spectroscopy has been used to characterize neutron-irradiated cubic SiC samples after thermal annealing in the 200-1100^OC temperature range. Three new paramagnetic defects named Ky6, Ky7 and Ky8 have been revealed. Based on the present results, these defects have been tentatively attributed to the negatively charged carbon vacancy-carbon antisite pair, negatively charged divacancy and neutral carbon <100> split interstitial, respectively. Furthermore, the finding of practically isotropic hyperfine splitting for EPR lines of the T6 center confirms its assignment as a carbon vacancy-interstitial pair.

Abstract: Only a few methods exist to observe, identify, and localize defects in SiC devices. These defects are a major limit for device performance and reliability. Presented is an improved experimental setup to investigate deep level defects using electrically detected magnetic resonance (EDMR). The method applied in this study exploits the simultaneous in-situ electron spin resonance (ESR) measurement of a standard sample (DPPH) to calibrate the magnetic field. The functionality is shown by comparing the data of an ion implanted SiC diode to results from a recent study . The in-situ B-field calibration is found to increase the accuracy of EDMR measurements by a factor of 2.5.

Abstract: The irradiation with 0.9 MeV electrons and with 8 MeV and 15 MeV protons were performed for studying radiation defects. Proton scattering in a silicon carbide film has been numerically simulated. Distribution histograms of the energy imparted to recoil atoms are obtained. Two energy ranges are considered when analyzing the histograms. In the first range of “low” energies, individual Frenkel pairs with closely spaced components are created. In the second range, recoil atoms have energies sufficient for generating a cascade of displacements. This gives rise to microscopic regions with high density of vacancies and vacancy complexes of various kinds.

Abstract: We have characterized deep levels in as-grown and electron irradiated p-type 4H-SiC epitaxial layers by the current deep-level transient spectroscopy (I-DLTS) method. A part of the samples were irradiated with electrons in order to introduce defects. As a result, we found that electron irradiation to p-type 4H-SiC created complex defects including carbon vacancy or interstitial. Moreover, we found that observed deep levels are different between before and after annealing, and thus annealing may change structures of defects.

Abstract: Deep Level Transient Spectroscopy (DLTS) investigations at different temperatures and with various filling pulse lengths were performed on n-type 4H-SiC epitaxial layers using Iridium Schottky contacts to determine the electrical capture process of the EH₆-center. The temperature dependence of the electrical capture cross section σ ~ T^-2.0 suggests a cascade capture process, which is not thermally activated. Together with earlier work by Zippelius et al. [4] this proves the acceptor-type of the EH₆-center.

Abstract: Using first-principles calculations, we investigated the migration mechanisms of Cl in cubic SiC. The analysis of the formation energies of several defect configurations (isolated interstitials and complex defects), either reported in the literature or calculated in the present study, revealed that three migration mechanisms are possible: Interstitialcy and two different vacancy-mediated mechanisms (both concerted exchange and second-neighbor hop). Our calculations showed that vacancy-mediated diffusion is more energetically favorable than an intersticialcy one and the values of the diffusivity, for both n-type and p-type SiC were also estimated.