We used single crystals of GaN, obtained from high-pressure synthesis, as substrates for Metalorganics Vapor Phase Epitaxy growth of violet and UV laser diodes. The use of high-quality bulk GaN leads to the decrease of the dislocation density to the low level of 105 cm−2, i.e. two orders of magnitude better than typical for the Epitaxial Lateral Overgrowth laser structures fabricated on sapphire. The low density and homogeneous distribution of defects in our structures enables the realization of broad stripe laser diodes. We demonstrate that our laser diodes, having 15 μm wide stripes, are able to emit 1.3-1.9 W per facet (50% reflectivity) in 30 ns long pulses. This result, which is among the best ever reported for nitride lasers, opens the path for the development of a new generation of high power laser diodes.

The properties of nanocrystals were studied by in-situ high-pressure powder diffraction technique using our methodology of the structural analysis, the “apparent lattice parameter” (alp) concept. The experiments were performed for nanocrystalline SiC and diamond powders using synchrotron and neutron sources and hydrostatic or isostatic pressure. Elastic properties of the samples were examined based on the measurements of the lattice parameters and of the reflection width, as well as of interatomic distances. The results show a dual nature of the properties (compressibilities) of the powders indicating a complex, core-shell structure of the grains.

Compacts of composites SiC-diamond were made by infiltration of Si into nanocrystalline diamond powders in a toroid-type press under the pressure of 7.7 GPa at 1300 °C. In-situ high pressure diffraction studies of these processes were performed in MAX80 cubic anvil press at a pressure of 8.5 GPa in temperatures up to 1800°C in HASYLAB at DESY, Hamburg, Germany. Sintering was performed for (i) pure nanocrystalline diamond powders, (ii) a mixture of nanocrystalline powders of diamond and nanocrystalline SiC, (iii) a mixture of nanocrystalline diamond with microcrystalline Si powders and (iv) compacts of nanocrystalline diamond infiltrated by Si. The SiC-diamond composites obtained by infiltration of Si have best physical properties: hardness similar to conventional diamond compacts (approximately 50 GPa), highest density 3.35 g cm-3 and uniform nanocrystalline microstructure.