We report on the first observation of the electron paramagnetic resonance of iron impurity in SiC:Fe crystals. Iron exists in the Fe3+ (3d5) charge state with electron spin S = 5/2 and seems to occupy silicon sites in the 6H-SiC lattice. The EPR spectrum of Fe3+ in SiC shows a characteristic anisotropy of an S = 5/2 system in a strong axial crystalline field with fine structure parameter D = 0.25 cm-1. The g-factor is nearly isotropic, g = 1.99. The possibility of using iron doping to obtain semi-insulating SiC crystals is discussed.
The interrelationships among implantation-induced defect density, carrier activation rate, substrate temperature during nitrogen implantation and annealing in 6H–SiC have been clarified. Several defects, whose energy required for recovery of lattice damage depends on the substrate temperature during implantation, were examined. Although defect density was sufficiently low that it was undetectable by Rutherford backscattering spectrometry, the carrier activation rate was 3.3% under the condition that the implanted nitrogen density was 1.8×1019 cm-3. According to the first principles local-density functional calculation using the cubic SiC crystal model, the complex defect composed of interstitial carbon and substituted nitrogen, which produces a localized electronic state and a half-occupied level in the band gap, is considered to be one cause of the low carrier activation rate in nitrogen-implanted SiC.
Electronic grade wafers of 6H SiC have been given a surface oxide layer on the carbon face by either conventional thermal oxidation or low-temperature plasma oxidation. Transmission electron microscopy, energy-dispersive x-ray and parallel electron energy loss, have been used to characterize the layer and its interface with the parent carbide. In both cases the oxide is close to Si2CO6 in composition but has a higher oxygen content at the surface. The plasma-grown oxide displays a higher proportion of p-bonded carbon than the SiC substrate does.
Deep level transient spectroscopy is employed in order to assess whether E-beam metal deposition on bulk n-type 6H–SiC effects any changes to the underlying material. Near-surface E-beam-related damage is shown to be device specific. The EB1-related defect at Ec − (0.346 ± 0.007) eV with σna = (5.4+1.5−1.2) × 10−16 cm2 and the EB2-related defect at Ec − (0.47 ± 0.01) eV with σna = (2.2+0.5−1.7) × 10−15 cm2 are detected in several devices, independently of the metal used for deposition. It is shown that the broad EB3 peak, detected in a set of E-beam fabricated devices, corresponds to the p5-related band of interface states also detected in thermally metallized devices. It is shown that neither the EB3 nor the p5 peak can be detected in environmentally aged E-beam fabricated devices. This is attributed to interface state passivation via in-diffusion of atmospheric oxygen.
We have investigated the trap centers in germanium-ion-implanted SiC(6H-SiC:Ge) and in as-grown SiC(AG:6H-SiC) samples using photoluminescence (PL) and deep-level transient spectroscopy (DLTS). Three carbon-vacancy related luminescence peaks were observed in 6H-SiC:Ge in PL measurements. Six electron trap centers were observed both in 6H-SiC:Ge and in AG:6H-SiC by DLTS. These trap-center-related peaks disappeared from both 6H-SiC:Ge and AG:6H-SiC after surface oxidation and subsequent removal of the oxide layers. Germanium atoms related to donor-type deep level at 1.2 eV below the conduction band edge is observed in 6H-SiC:Ge by DLTS. The six common trap centers are related to native defects. The deep-level activation energy, concentration and capture cross section are estimated.
Knowledge of absorption coefficient values for wavelengths above the bandgap and the injected carrier density profile is an important issue for analysis of carrier dynamics in highly excited semiconductors, e.g. for evaluation of the carrier density in photoexcited layer, density-dependent recombination rate and diffusivity. In this work we present a novel way for determining the interband absorption coefficient α for SiC crystals in a wide temperature range. The proposed method is based on recording of a transient free carrier grating in a bulk semiconductor by strongly absorbed light and measurements of probe beam diffraction efficiencies on the grating for the Bragg and symmetric anti-Bragg directions. The method was applied for 3C-, 6H--SiC polytypes, 4H-SiC polytypes at 351 nm wavelength and revealed 3 to 10-fold increase in the interband absorption coefficients in the 80–800 K temperature range. Increase in absorption coefficients with temperature was simulated by bandgap shrinkage and increase in phonon density. A good agreement of the determined α values with a priori known room-temperature data verified validation of this technique.
On the base of the physical analytical models based on Poisson's equation, drift–diffusion and continuity equations the forward current–voltage characteristics of 6H-SiC and 4H-SiC type Schottky diode with Ni and Ti Schottky contact have been simulated. It is shown on the base of analysis of current–voltage characteristics in terms of classical thermionic emission theory it is shown that the proposed simulation model of Schottky diode corresponds to the almost "ideal" diode with ideality factor n equals 1.1. Because of this it is determined that the effective Schottky barrier height phivB equals 1.57 eV and 1.17 eV for Ni/6H and Ti/4H silicon carbide Schottky diode type, respectively.