Abstract: Deep levels in as-grown p-type 4H-SiC epilayers have been investigated by DLTS. Three
deep hole traps (HK2, HK3 and HK4) can be detected by DLTS in the temperature range from 350K
to 700K. They are energetically located at 0.84 eV (HK2), 1.27 eV (HK3) and 1.44 eV (HK4) above
the valence band edge. The activation energy of the traps does not show any meaningful change
regardless of applied electric field, indicating that the charge state of the deep hole traps may be
neutral after hole emission (donor-like). By the low-energy electron irradiation, the HK3 and HK4
concentrations are significantly increased, suggesting that the origins of the HK3 and HK4 may be
related to carbon displacement. Study on the thermal stability of these hole traps has revealed that the
trap concentrations of HK3 and HK4 are reduced to below the detection limit (1-2 × 1011 cm-3) by
annealing at 1350°C. The HK2 is thermally more stable than HK3 and HK4, and becomes lower than
the detection limit by annealing at 1550°C.
Abstract: A variety of 4H-SiC samples from undoped crystals grown by the physical vapor
transport technique have been studied by temperature dependent Hall effect, optical and thermal
admittance spectroscopy and thermally stimulated current. In most samples studied the activation
energies were in the range 0.9 - 1.6 eV expected for commercial grade HPSI 4H-SiC. However, in
several samples from developmental crystals a previously unreported deep level at EC-0.55 ± 0.01
eV was observed. Thermal admittance spectroscopy detected one level with an energy of about
0.53 eV while optical admittance spectroscopy measurements resolved two levels at 0.56 and 0.64
eV. Thermally stimulated current measurements made to study compensated levels in the material
detected several peaks at energies in the range 0.2 to 0.6 eV.
Abstract: Thermally stimulated current spectroscopy (TSC) has been applied to characterize deep
traps in high-purity semi-insulating 6H-SiC substrates. By using above bandgap to sub-bandgap
light for illumination at 83 K and different applied biases, at least nine TSC traps in the temperature
range of 80 to 400 K can be consistently observed. It is found that TSC peaks for T < 130 K are
significantly affected by light and some peaks are strongly enhanced by the applied bias. Measured
trap activation energies range from 0.15 eV to 0.76 eV. Theoretical fittings of selected traps give
more accurate trap parameters. Based on literature results connected with deep traps in conductive
6H-SiC, the origin of these TSC traps is discussed.
Abstract: In this paper superlinear dependence in the intensity–current characteristic, optical and
temperature quenching of photocurrent and photoelectric memory in structures made on the basis of
compensated 6H-SiC at room and high temperatures are reported. The maximal time of decreasing
of the residual current was 5*104 s. With illumination by additional light with 0.62 μm wavelength
and increasing of the applied voltage the value of residual current can be changed. The depth
sensitivity centre is positioned at Ec -1.1eV and the cross section of captured holes on this centre is
10-21-10-22 cm2 based on our measurements.
Abstract: The high resistivity of SiC required for many device applications is achieved by
compensating residual donors or acceptors with vanadium or intrinsic defects. This work addresses the
defect levels of substitutional vanadium and the positively charged carbon vacancy (VC
+) in semiinsulating
(SI) SiC. After reviewing the earlier studies related to both defects, the paper focuses on
temperature-dependent Hall measurements and photo-induced electron paramagnetic resonance (EPR)
experiments of 4H and 6H SI SiC. In vanadium-doped samples, a V3+/4+ level near Ec-1.1 eV (4H) and
Ec-0.85 eV (6H) is estimated by a comparison of dark EPR spectra and the activation energy
determined from the Hall data, assuming that vanadium controls the Fermi level. In high purity semiinsulating
substrates, analysis of time-dependent and steady-state photo-EPR data suggests that the
plus-to-neutral transition of the carbon vacancy involves a structural relaxation of about 0.6 eV.
Abstract: Only recently the well-resolved hyperfine structure of the P6/P7 EPR center has
been experimentally observed. Based on the calculated hyperfine tensors we assign the P6/P7
center to the high spin state neutral divacancy, which is the ground state in agreement with
the experiment. We propose a mechanism to explain the loss of divacancy signal at high tem-
perature annealing in semi-insulating SiC samples. We discuss the possible correlation between
the divacancy and some photoluminescence centers.
Abstract: Electron paramagnetic resonance (EPR) studies of the P6/P7 centers in 4H- and 6H-SiC
are reported. The obtained principal values of the hyperfine tensors of C and Si neighbors are in
good agreement with the values of the neutral divacancy (VCVSi
0) calculated by ab initio supercell
calculations. The results suggest that the P6/P7 centers, which were previously assigned to the
photo-excited triplet states of the carbon vacancy-carbon antisite pairs in the double positive charge
2+), are related to the triplet ground states of the C3v/C1h configurations of VCVSi
Abstract: High temperature anneals were used to study the evolution of native defects in semiinsulating
(SI), ultrahigh purity SiC using electron paramagnetic resonance (EPR), infrared and
visible photoluminescence (PL) and COREMA (Contactless Resistivity Mapping) measurements.
In EPR we observe a defect that we tentatively identify as VC-CSi-VC. The EPR intensities of this
defect and the UD1 IRPL increase significantly with annealing in all samples.
Abstract: P6 and P7 centers, which are responsible for semi-insulating properties of SiC,
were shown to be neutral Si-C divacancies (VSi-VC)o having a triplet ground state. The EPR
experiments that were performed at very low temperatures and in complete darkness exclude
the possibility of a thermal or optically excited triplet state and, as a result, the existing model
of excited triplet state P6 and P7 centers was discarded. The optical alignment process which
induces the spin polarization of the ground triplet 3A state of the P6, P7 centers in SiC was
interpreted to be caused by strong spin selectivity of the intersystem crossing (ISC) nonradiative
transitions from an excited 3E state to a metastable singlet 1A state. The
luminescence and optical absorption are caused by transitions between spin sublevels of 3A
and 3E states. The analogy in properties of a divacancy in SiC and the N-V defect in diamond
allows considering the divacancy in SiC as a potential defect for the single defect
Abstract: The negative carbon vacancy antisite complex is analysed by ab initio theory in view of the
SI5 EPR-center. The complex occurs in a Jahn-Teller distorted ground state and a meta stable state.
This and the calculated hyperfine structure agree nicely with the temperature dependent EPR spectra
of SI5. An interpretation of the photo-EPR experiments is proposed.