Materials Science Forum Vols. 483-485

Abstract: The electronic and structural properties of nickel-vacancy complexes in diamond were investigated by a total energy ab initio methodology. These results are discussed in the context of the electrically active centers, commonly found in synthetic diamond.

Abstract: We carried out a theoretical investigation on the properties of manganese impurity centers in cubic boron and gallium nitrides. The calculations were performed using the all electron spin-polarized full-potential linearized augmented plane wave methodology. Our results indicate that manganese in boron nitride, in a neutral charge state, is energetically more favorable in a divacancy site as compared to a substitutional cation site. We present the results on stability, spin states, impurity magnetic moment, hyperfine parameters, and formation and transition energies of manganese at the divacancy site in several charge states.

Abstract: Due to the lack of GaN wafers, so far, group-III nitrides are mostly grown on sapphire or SiC substrates. Silicon offers an attractive alternative because of its low cost, large wafer area, and physical benefits such as the possibility of chemical etching, lower hardness, good thermal conductivity, and electrical conducting or isolating for light emitting devices or transistor structures, respectively. However, for a long time, a technological breakthrough of GaN-on-silicon has been thought to be impossible because of the cracking problem originating in the huge difference of the thermal expansion coefficients between GaN and silicon which leads to tensile strain and cracking of the layers when cooling down. However, in recent years, several approaches to prevent cracking and wafer bowing have been successfully applied. Nowadays, device-relevant thicknesses of crackfree group-III-nitrides can be grown on silicon. To reach this goal the most important issues were the identification of the physical origin of strains and its engineering by means of in situ monitoring during metalorganic vapor phase epitaxy.

Abstract: 90 Shockley partial dislocations in GaN are investigated by first-principles calculations. This work is focussed on the electrical properties of dislocation cores, and on investigating the electrical fields around these defects. The band structure analysis shows that both the  and  core partials possess a midgap state. The -core dislocations give rise to a donor level Ev +0:87 eV that might explain the absorption peak at 2.4 eV revealed by energy loss spectroscopy measurements. The acceptor level Ev + 1:11 eV localized at the -core dislocations might contribute to the yellow luminescence. These dislocations experience a substantial charge polarization along the [0001] growth axis. In addition, we show that these dislocations tend to charge in a high stress field.

Abstract: In this communication we present the results of study of new contact systems to GaN epitaxial layers grown on sapphire and n-type 6H-SiC monocrystals. The TiBx nanostructure phase has been used during manufacturing Ti – Al – TiBx – Au and TiBx contact systems. The n-GaN epitaxial layers of 1 µm thickness were grown on [0001] sapphire substrate by vapor-phase epitaxy. The n-type 6H-SiC monocrystals were grown by Lely method with the donor concentration of 2x1018 cm3. The layers of Ti, Al, TiBx and Au were deposited by magnetron sputtering followed by high-temperature annealing.

Abstract: The surface morphology of the ZnO layers is dominated by a distinct hexagonal domain structure. While the laterally integrated cathodoluminescence spectrum shows intense and narrow I8 luminescence, a distinct emission line at spectral position of I0/I1 emerges in the local spectra taken at domain boundaries. In contrast, no I0/I1 emission is found inside the domains. Monochromatic images further evidence the selective incorporation of impurities at the grain boundaries of domains. Monochromatic images of the I8 peak wavelength directly visualize the strain relaxation across the domains towards their very center, where a drop in quantum efficiency indicates enhanced defect concentration.