Abstract: We present new electron-paramagnetic-resonance (EPR) data on the HEI4/SI5 center in
4H-SiC. So far, the SI5 (SI-5) center has been observed only in as-grown SiC substrates; however, we
found that it can be created by electron irradiation to commercial n-type 4H-SiC. The artificially
created SI5 center, which we had preliminary called HEI4, was found to be identical with the SI5
center in as-grown SiC. A high-intensity HEI4/SI5 spectrum of irradiated SiC revealed clear
hyperfine structures of 29Si and 13C, which enabled us to identify the origin of this center as a carbon
antisite-vacancy pair in the negative charge state (CSi-VC
–). We assessed its electronic levels using
Abstract: Two types of a new triplet centers labeled as N-V have been observed in heavily neutron
irradiated (dose of 1021 cm-2) and high-temperature annealed (2000°C) 6H-SiC crystals. The centers
have an axial symmetry along c-axis. Anisotropic hyperfine splitting due to the one 14N nucleus has
been observed. The EPR spectra of N-V defects in the triplet state in 6H-SiC reveal strong
temperature dependence. The parameters of these centers are similar to that for well-known N-V
center in diamond. It seems to consist of silicon vacancy and carbon substitutional nitrogen in the
adjacent lattice cites oriented along c-axis. Similar to the diamond N-V centers in SiC have been
produced by neutron irradiation and high-temperature annealing of the crystals containing nitrogen.
For the first shell the structure of the N-V defect in 6H-SiC is practically identical with that in
diamond. The charge state of this defect seems to be +1 compare with neutral state for nitrogensilicon
vacancy defect in 6H-SiC with S=1/2.
Abstract: The decay kinetics of a persistent photoconductivity (PPC) in undoped semi-insulating
4H SiC and intercenter charge transfer were studied with EPR, photo-EPR and optical admittance
spectroscopy (OAS). A thermally activated charge transfer process that occurs in the dark has been
observed. The PPC effect was observed directly in changes in the quality factor of the EPR cavity
before and after illumination and by the decay of the OAS signal for deep levels, and indirectly by
the excitation and decay of the nitrogen and boron EPR lines that were not observed in the dark
before illumination. The decay kinetics of the PPC and photo-induced carrier capture by nitrogen
and boron levels were found to follow a stretched exponential form. The PPC in the temperature
range from 77 to 300K was found to be produced by a thermally induced charge transfer process
involving deep trap levels.
Abstract: In this study, we report on the observation of recombination center defects in the base of
4H-SiC bipolar junction transistors. The defects are observed through a very sensitive electrically
detected electron spin resonance technique called spin dependent recombination. To the best of our
knowledge, these results represent the first electron spin resonance results of any kind reported in a
fully processed SiC bipolar junction transistor and provide the first direct observations of the
chemical and physical nature of recombination centers in SiC bipolar junction transistors. Our
results clearly demonstrate the power of SDR techniques in the detection of recombination centers
in SiC bipolar junction transistors.
Abstract: In this work we used Positron Annihilation Spectroscopy (PAS) and Electron
Paramagnetic Resonance (EPR) to investigate the properties of vacancy defects produced by low
energy electron irradiation. N-doped 3C-SiC and 6H-SiC monocrystals have been irradiated with
electrons at different energies from 240keV to 900keV. EPR measurements show that Frenkel pairs
3-/Si are created in 6H-SiC when electron irradiation is performed at low energy (240-360 keV).
EPR also indicates that the silicon displacement threshold energy is higher in 3C-SiC than in 6HSiC.
Moreover, PAS results show that the size and concentration of the vacancy defects decrease
when the electron energy decreases for both polytypes. PAS detects vacancy defects in 240keV
electron irradiated 3C-SiC, and the detection of the carbon vacancy is proposed.
Abstract: Positron annihilation radiation Doppler broadening spectroscopy was used to study defects
in semi-insulating (SI) silicon carbide (SiC) substrates grown by high-temperature chemical vapour
deposition (HTCVD). The Doppler broadening measurements show (i) that the measured samples
contain vacancy clusters (ii) that the positron trapping to the clusters is increased in annealing (iii)
that the chemical environment of the defects in the un-annealed samples is different from those of the
Abstract: We study electronic Raman scattering of phosphorus and nitrogen doped silicon
carbide (SiC) as a function of temperature in the range 7K < T < 300K. We observe a
series of peaks in the Raman spectra which we assign to electronic transitions at nitrogen
and phosphorus donors on different lattice sites. These transitions are identified as valley orbit
transitions of the 1s donor ground state. From the polarization dependence of the observed
peaks, we find that all electronic Raman signals have E2-symmetry of C6v for the hexagonal
polytypes (6H-SiC and 4H-SiC) and E-symmetry of C3v for 15R-SiC. We find a reduction of
the intensities of all valley-orbit Raman signals with increasing temperature and ascribe this
reduction to the decreasing occupation of donor states.