Search

With electron nuclear double resonance the superhyperfine interactions of numerous 29Siand 13Clattice neighbours of 14Ndonors in 3C and 4H–SiC have been measured. It was attempted to explain them using the effective mass theory (EMT). The interactions of N donors on cubic sites in 3C–SiC can be well explained with EMT assuming N to be on C sites, but not on Si sites. N in 3C–SiC represents probably the only true EMT donor, since for shallow donors in Si EMT is not sufficient as shown previously. The interactions of N on the hexagonal sites in 4H–SiC are still reasonably well explained, while the EMT approach fails to explain N on the quasi-cubic sites. Comparison between 3C–SiC and 4H–SiC shows that the “central cell corrections” due to the chemical nature of N introduced into EMT previously for silicon is very small. The major contribution comes from inter-valley interactions.

In Sc-doped 6H–SiC epitaxial layers we observed several different electron paramagnetic resonance (EPR) spectra with a 45Schyperfine interaction pattern. The spectra are explained as being due to the isolated Sc0(S=12)acceptor on carbon sites but with different microscopic configurations. The spectra show a pronounced temperature dependence. At low temperatures the hole of the Sc0acceptor is located in a Sc0–Si bond either along the c-axis forming an axial centre or along one of the three other C–Si bonds giving rise to a monoclinic centre. At higher temperature the hole changes place rapidly between the three Sc–Si bonds resulting in an axial centre. All three Sc0hole configurations have different ionisation levels. The ionization level of the low-temperature monoclinic–high-temperature axial centre is significantly influenced by an entropy term. In 4H–SiC spectra were only observed from a single Sc0centre with monoclinic symmetry.

We show that a deep level, the ES1, introduced in n-GaN by sputter-deposition of gold Schottky contacts exhibits metastable-like behaviour during temperature cycling between 55 and 250K. The ES1 has an energy level 0.22±0.02eV below the conduction band. We provide some evidence that indicates that the defect responsible for the ES1 has a second energy level, the ES1∗, and that the metastable behaviour of the ES1 may be due to negative-U ordering of these two energy levels. Furthermore, field effect measurements indicate that the ES1 level has a donor character, while the ES1∗level is probably an acceptor.

We have used deep-level transient spectroscopy (DLTS) to study the electrical properties of defects introduced in epitaxial n-GaN during electron beam (EB) deposition of Ru Schottky contacts. DLTS revealed that EB deposition introduces at least two defects, Ee1 and Ee2, with energy levels at EC−(0.19±0.01)eV and EC−(0.92±0.04)eV, respectively, in the band gap. The defect Ee1 has a similar signature as a radiation induced defect in GaN, speculated to be the VN. The concentrations of Ee1 and Ee2 both decrease away from the interface into the GaN. The concentration of Ee2, the more prominent of the two defects, is estimated as about 1016cm−3at the GaN surface. The effect of the EB deposition induced defects on the current–voltage characteristics of the Schottky contacts thus formed is to introduce recombination and generation components to the reverse and forward currents, respectively.