Irradiated 4H-SiC Research Articles

Defect annealing kinetics in irradiated 6H–SiC

Isochronal and isothermal annealing of ion-irradiation damage on the Si sublattice in 6H–SiC has been investigated experimentally by in situ Rutherford backscattering spectrometry in channeling geometry (RBS/C). At low ion fluences corresponding to dilute concentrations of irradiation-induced defects, complete recovery of disorder on the Si sublattice can occur below room temperature. The implantation of helium impedes the defect recovery processes at low temperatures. Below room temperature, the thermal recovery of defects on the Si sublattice has an activation energy on the order of 0.25±0.1 eV. Recovery of disorder on the Si sublattice above 570 K has an activation energy on the order of 1.5±0.3 eV.

Infra-red reflectivity of ion-implanted and pulsed excimer laser irradiated 4H-SiC

Infrared reflection measurements at near normal incidence between 400–7800 cm−1 have been performed on ion implanted bulk and epitaxial 4H-SiC. Three samples were triple implanted with N14 at 30, 80, and 140 keV to achieve a flat dopant profile. A fourth sample was implanted at 20, 40 and 60 keV at a temperature of ∼830 K in-order to reduce lattice damage. We make use of the Reststrahlen band, situated between the Transverse Optical (TO) ωTO and the Longitudinal Optical (LO) ωLO phonon modes to investigate both the damage created by ion-implantation and the lattice recovery induced by subsequent XeCl excimer laser (308 nm) annealing. We show that an optimum incident laser fluence between 0.9 and 1.0 J/cm2 exists for lattice recovery.

Defect Structures in Neutron Irradiated 6H-SiC Studied by X-Ray Diffraction Line Profile Analysis

ABSTRACTWe have investigated by x-ray diffraction defect structures in 6H-SiC after neutron irradiation with different fluences and followed by different annealing procedures. An interpretation along a model of Klimanek [1, 4–6] shows, that higher fluences lead to a stronger than linear reduction of the correlation length, whereas higher annealing temperatures correlate with a better recovery of the correlation length. In addition defects of 1st kind created by irradiation are reduced by annealing. We find that annealing changes the character of the defects and it accentuates a defect structure already present in the original samples.

Damage formation and recovery in C +-irradiated 6H–SiC

Single crystals of 6H–SiC were irradiated with 550 keV C + ions over a range of temperatures (180–870 K) and ion fluences (1 × 10 18 to 5 × 10 19 C +/m 2). The damage induced by the irradiation ranged from dilute defect concentrations up to buried amorphous layers. Damage recovery in the samples irradiated at 180 K has been followed by isochronal annealing (20 min) at 300, 470, 670 and 870 K. The accumulation and recovery of atomic disorder on the Si sublattice has been studied using in situ Rutherford Backscattering Spectrometry in combination with ion channeling methods (RBS/C). The disordering rate shows a sigmoidal dependence on dose at each irradiation temperature. Simultaneous defect recovery processes occur during irradiation at room temperature, and post-irradiation thermal defect recovery is also observed at room temperature.

Excitation properties of SiC photoluminescence

We report on photoluminescence excitation (PLE) studies of defect luminescence in SiC. Two examples are given illustrating the main advantages of the technique. First, the benefits of selective excitation are shown in sorting out a complicated PL spectrum in electron irradiated 4H-SiC. Secondly, the possibility of detecting high energy excited states is demonstrated by the PLE spectrum of the D1 centre in 4H-SiC

The D1 Exciton in 4H-SiC

We report on the properties of the D1 photoluminescence (PL) observed in electron irradiated 4H-SiC. We have investigated the temperature dependence of the PL and its excitation properties. At 2 K the D1 PL spectrum in 4H-SiC consists of one no-phonon line, L1 (2.9010 eV), and its phonon replicas. As the temperature is raised, two higher energy no-phonon lines, M1 (2.9087 eV) and H1 (2.9118 eV), appear while the L1 intensity rapidly decreases. At temperatures between 100 and 200 K the D1 PL is quenched. The associated activation energy is found to be approximately 57 meV. The PL excitation (PLE) spectrum of the L1 no-phonon line at 2 K contains two strong peaks corresponding to the M1 and H1 lines. Furthermore, there is a series of sharp PLE peaks at higher energies. The energy positions of these lines can be fitted by a hydrogenic series of excited states with an associated binding energy of 53 meV. Our results can be explained by exciton recombination at an isoelectronic centre. One of the particles of the exciton is weakly bound, whereas the other is more tightly bound.

Observation of Metastable Defect in Electron Irradiated 6H-SiC

Observation of Metastable Defect in Electron Irradiated 6H-SiC

Characterization of Defects in Electron Irradiated 6H-SiC by Positron Lifetime and Electron Spin Resonance

Characterization of Defects in Electron Irradiated 6H-SiC by Positron Lifetime and Electron Spin Resonance

Bound Exciton Recombination in Electron Irradiated 4H-SiC

Bound Exciton Recombination in Electron Irradiated 4H-SiC

Damage Response to Irradiation Temperature and Ion Fluence In C+-Irradiated 6H-SiC

AbstractIrradiation experiments have been performed 60° off the surface normal for 6H-SiC single crystals at various temperatures (185-870 K) using 550 keV C+ ions over a fluence range from 1×1018 to 5×109 ions/m2. Atomic disorder on the Si sublattice, as determined by in-situ RBS/channeling analysis, ranged from dilute defects to complete amorphization. The critical amorphization dose of ∼0.23 dpa (on the Si sublattice) at 185 K has been determined. Asymmetric shapes in angular yield profiles across the crystallographic axis <0001> emerged above 1.5×1019 C−/m2 (∼0.05 dpa in the near-surface region), which might be associated with the lattice disturbance in the crystal structure. A gradual decrease in half-angular width was observed with the increase of ion fluence in the experiment. The minimum yield exhibits a rather linear relationship with ion dose at the surface. Post-irradiation annealing at the irradiation temperature did not result in measurable recovery for fluences ranging from 4 × 1018 to 2×1019 C+/m2 at 300, 470 and 670 K. Results also show that low fluence (<8×1018 C+/m2) irradiation at 185 K followed by thermal annealing results in similar defect concentrations to irradiation at that same temperature to the same ion fluence. Thus, at low fluences, the accumulated defects are in thermal equilibrium with the structure.

Capacitance transient studies of electron irradiated 4H-SiC

Deep level defects in electron-irradiated 4H-SiC epilayers grown by chemical vapor deposition (CVD) were studied using deep level transient spectroscopy (DLTS). DLTS measurements performed on electron-irradiated p + n junctions in the temperature range 100–7.50 K have revealed seven electron traps. Most of these defects were already observed at a dose of irradiation as low as 5 × 10 13 cm −2. Dose dependence and annealing behaviour of the defects were investigated. For two of these electron traps, the capture cross section was measured.

Vacancies In Electron Irradiated 6H-SiC

AbstractAnnealing of electron irradiated bulk n-type 6H-SiC has shown that neutral carbon vacancies and neutral silicon vacancies undergo a major reduction in concentration in the 20–200 °C temperature interval after which only slight changes occur up to 1200 °C. The experiments suggest that the positively charged carbon vacancy, detected by electron paramagnetic resonance, constitutes only a small fraction of all carbon vacancies.