Novel functionality and material were developed for Si-photonics in this study. Ultra-fast silicon all optical switches using two-photon absorption (TPA) were developed in silicon nanowire optical waveguide on silicon-on-insulator substrate. This waveguide can produce high optical intensities that yield optical nonlinearity such as TPA even at input optical powers typically used in fiber optic communication systems. In addition, we fabricated a GaSb based quantum well (QW) on a Si substrate. The emission wavelength of QW was 1.55 µm at room temperature, so that the new function can be developed on Si-photonics using this QW.

We have fabricated a novel type of intrinsic Josephson junctions with superconducting Bi2Sr2CaCu2O8+y (Bi-2212)/YBa2Cu3O7-x(YBCO) bilayer thin films deposited on MgO(100) substrates. We used the 4th harmonics of a Nd:YAG pulsed laser ablation. Furthermore, we studied the transport properties of a 25 µm 25 µm Bi-2212/YBCO mesa-type junction. The zero resistance temperature was around 50 K. The current-voltage characteristics showed flux-flow-like behavior and a supercurrent of about 2 mA at 4.2 K. Shapiro steps were observed when microwave was irradiated to the mesa junction. These Shapiro steps are attributed to the Josephson junction formed at the interface between the Bi-2212 and YBCO layers in the mesa structure and not to the intrinsic Josephson junctions in the Bi-2212 layer or the micro-grains within the films.

Dislocation properties in InGaN/GaN Quantum Wells and GaN grown on bulk GaN and sapphire substrates by metalorganic chemical vapor deposition (MOCVD) were characterized using cathodoluminescnece (CL), transmission electron microscopy (TEM), atomic force microscopy (AFM) and photoluminescence (PL). It was clearly demonstrated that dislocations act as nonradiative recombination centers in both n-type (undoped and Si-doped) GaN and InGaN layers. Furthermore the very short-minority carrier diffusion length was a key parameter to explain the high light emission efficiency in GaN-based light emitting diodes (LEDs) prepared on sapphire substrates. On the other side band-tail states were detected in the heteroepitaxial InGaN layers only by temperature dependence PL measurement. Additionally InGaN phase separation, which consists of few micron domains, has been produced under growth conditions which favors the spiral growth. These results indicate that the dislocations in the InGaN layers act as triggering centers for the InGaN phase separation which cause both a compositional fluctuation and the formation of few micron phase separated domains. The homoepitaxial InGaN layers showed however quite normal behaviors for all characterizations.