Abstract: In 4H-SiC, 3C stacking fault (SF) behaves like a finite thickness type II quantum well. As a consequence, it can bind two excitons per well. We show in this work that, as the SF thickness increases, the relative intensity of the two transitions changes. This comes from a change in the wave functions overlap between the electron trapped in the well and the holes trapped neighbouring parts of the 4H-SiC matrix.
Abstract: Focussing on the fine structure of excitons bound to large 2-dimensional stacking faults in a 4H-SiC matrix, we show that the intrinsic type-II nature of the band alignment, combined with the effect of the spontaneous polarization, should result in a double bound-exciton signature per well. Then, we present the first observation of a 3C-QW sandwiched between two higher energy bandgap polytypes in a 3C-SiC matrix.
Abstract: Deep levels in 4H- and 6H-SiC are characterized by FTIR spectroscopy. Vanadium,
chromium and the silicon vacancy related center are listed together with the unidentified defects with emission and absorption in the near IR region. We suggest the UD-1, UD-3 and I-1 to be impurity related while the UD-2 and UD-4 to be intrinsic defects based on annealing behavior and the possibility to create the defect with irradiation. We have also tentatively assigned a new defect center around 1.0 eV to the carbon vacancy-antisite pair instead of the earlier assignment to the UD-
2 defect in 4H-SiC. We have shown that to get more information about the SiC samples a combination of absorption and luminescence techniques are very useful. Further, the use of below bandgap selective excitation is necessary to obtain more information about the defects present in the sample. FTIR absorption and luminescence measurements are useful tools to characterize deep levels important for both semi-insulating material as well as low doped conducting material where the free carrier lifetime is limited by deep levels.
Abstract: New results are presented concerning several optical centres having local vibrational modes in electron irradiated and annealed 4H and 6H SiC. Some of these centres are common to both polytypes, others have only been found in 6H SiC. They appear, typically, after annealing in the range 1000°C - 1300°C. Additional results have been obtained about mode splitting from 13C isotope enriched 6H SiC.
Abstract: Shallow N donors in n-type 4H-SiC were studied by electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR). For the N donor at the cubic site (Nk) in 4H-SiC, the hyperfine (hf) constants of the interaction with the nearest neighbour (NN) 29Si atom along the c axis were determined as A = 41.07 MHz and A^ = 41.31 MHz. For other three NN Si
atoms in the basal plane, the hf tensor has C1h symmetry and the principal values Axx = 5.94 MHz, Ayy = 5.06 MHz and Azz = 14.25 MHz. Our EPR and ENDOR observations unambiguously confirm that the N donor occupies the C site in 4H-SiC lattice and also reveal a considerable amount of the spin density of Nk (~23.9%) which was not obtained in previous studies.
Abstract: Midgap levels in 4H-SiC epilayers have been investigated by DLTS. The EH6/7 center (Ec-1.55 eV) is the dominant deep level as observed in DLTS spectra from n-type epilayers. The activation energy of EH6/7 center is unchanged regardless of applied electric fields, indicating that the charge state of EH6/7 center may be neutral after electron emission (acceptor-like). A DLTS spectrum
for a p-type epilayer in the temperature range from 90 to 830 K is dominated by two peaks, D center and a deep trap at 1.49 eV from the valence band edge. Minority carrier traps have been also investigated by DLTS using pn diodes. Two minority carrier traps with activation energies of 1.0 eV and 1.43 eV have been detected.
Abstract: The effects of irradiation with protons and electrons on 4H-silicon carbide epilayers were investigated. The particle energy was 6.5 and 8.2 MeV. The electronic levels associated with the irradiation-induced defects were analyzed by current-voltage characteristics and deep level transient spectroscopy measurements up to 700 K. In the same temperature range the apparent free carrier concentration was measured by capacitance-voltage characteristics to monitor possible
compensation effects due to the deep level associated to the induced defects. Introduction rate, enthalpy and capture cross-section of such deep levels were compared and some conclusions about the nature of the defects were drawn.
Abstract: Deep level transient spectroscopy (DLTS) was employed to investigate the annealing behaviour and thermal stability of radiation induced defects in nitrogen doped 4H-SiC epitaxial layers, grown by chemical vapor deposition (CVD). The epilayers have been irradiated with 15 MeV electrons and an isochronal annealing series has been carried out. The measurements have been performed after each annealing step and six electron traps located in the energy band gap range
of 0.42-1.6 eV below the conduction band edge (Ec) have been detected.
Abstract: Recombination enhanced defect annealing of intrinsic defects in 4H-SiC, created by low energy electron irradiation, has been observed. A reduction the defect concentration at temperature lower than the normal annealing temperature of 400º C and 800°C is observed after either above bandgap laser excitation or forward biasing of a pin-diode. The presence of the defects has been studied both electrically and optically using capacitance transient spectroscopy and low temperature photoluminescence. Photoluminescence measurements show that several lines, normally detected after electron irradiation, have almost or entirely disappeared by recombination enhanced annealing at room temperature. From capacitance transient measurements, the annealing enhancement is found
to be largest for the HS2 hole trap, while the EH1 and EH3 electron traps also anneal out by recombination enhanced reaction but at a lower rate.
Abstract: Photoluminescence (PL) and time resolved PL are well established as important
experimental techniques to study electronic properties of SiC. We studied the influence of ionimplantation on the photoluminescence peak at 423nm and the variation of the minority carrier lifetime (MCL).