We developed an electrically driven near-infrared broadband light source based on self-assembled InAs quantum dots (QDs). By combining emissions from four InAs QD ensembles with controlled emission center wavelengths, electro-luminescence (EL) with a Gaussian-like spectral shape and approximately 85-nm bandwidth was obtained. The peak wavelength of the EL was blue-shifted from approximately 1230 to 1200 nm with increased injection current density (J). This was due to the state-filling effect: sequential filling of the discrete QD electron/hole states by supplied carriers from lower (ground state; GS) to higher (excited state; ES) energy states. The EL intensities of the ES and GS emissions exhibited different J dependence, also because of the state-filling effect. The point-spread function (PSF) deduced from the Fourier-transformed EL spectrum exhibited a peak without apparent side lobes. The half width at half maximum of the PSF was 6.5 µm, which corresponds to the estimated axial resolution of the optical coherence tomography (OCT) image obtained with this light source. These results demonstrate the effectiveness of the QD-based device for realizing noise-reduced high-resolution OCT.

We have demonstrated switching characteristics in a wavelength switch based on multiple GaInAs/InP quantum wells. It consisted of straight arrayed waveguides with a linearly varying refractive index distribution. The refractive index can be changed via the thermo-optic (TO) effect. Using a Ti/Au thin-film heater to generate the TO effect, we realized four-port switching at four demultiplexed wavelengths. In addition, by changing the structure of the heater from rectangular to triangular, the power consumption for four-port switching was reduced by half.

Initial growth of GaP on Si substrates using metalorganic vapor phase epitaxy was studied. Si substrates were exposed to PH3 preflow for 15 s or 120 s at 830 after they were preheated at 925. Atomic force microscopy (AFM) revealed that the Si surface after preflow for 120 s was much rougher than that after preflow for 15 s. After 1.5 nm GaP deposition on the Si substrates at 830, GaP islands nucleated more uniformly on the Si substrate after preflow for 15 s than on the substrate after preflow for 120 s. After 3 nm GaP deposition, layer structures were observed on a fraction of Si surface after preflow for 15 s. Island-like structures remained on the Si surface after preflow for 120 s. After 6 nm GaP deposition, the continuity of GaP layers improved on both substrates. However, AFM shows pits that penetrated a Si substrate with preflow for 120 s. Transmission electron microscopy of a GaP layer on the Si substrate after preflow for 120 s revealed that V-shaped pits penetrated the Si substrate. The preflow for a long time roughened the Si surface, which facilitated the pit formation during GaP growth in addition to degrading the surface morphology of GaP at the initial growth stage. Even after 50 nm GaP deposition, pits with a density on the order of 107 cm-2 remained in the sample. A 50-nm-thick flat GaP surface without pits was achieved for the sample with PH3 preflow for 15 s. The PH3 short preflow is necessary to produce a flat GaP surface on a Si substrate.

We have successfully demonstrated a GaInAs/InP multiple quantum well (MQW)-based wavelength switch composed of the straight arrayed waveguide with linearly varying refractive index distribution by changing the refractive index using thermo-optic effect. Since optical path length differences between waveguides in the array were achieved through refractive index differences that were controlled by SiO2 mask design in selective metal-organic vapor phase epitaxy (MOVPE), wavelength demultiplexing, and the output port switching in each wavelength of light by the refractive index change in the array waveguides through the thermo-optic effect were achieved. We have obtained the wavelength switching and the change of transmission spectra in each output ports.

Effects of Fe/Si ratio and growth temperature were investigated in order to realize high quality Fe3Si/Ge structures. It was found that very small χmin values (2-3%) were achieved in a wide temperature range of 60-200 under the stoichiometric condition. From TEM observation, it was rvealed that the Fe3Si/Ge structures with atomically flat interfaces were realized. In addition, thermal stability of the Fe3Si/Ge structures was guaranteed up to 400. These results suggested that growth at a low temperature (<200) under the stoichiometric condition was essential to obtain high quality Fe3Si/Ge structures with sharp interfaces.

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 achieved first dynamic all-optical signal processing with a bandgap-engineered MZI SOA all-optical switch. The wide-gap Selective Area Growth (SAG) technique was used to provide multi-bandgap materials with a single step epitaxy. The maximum photoluminescence (PL) peak shift obtained between the active region and the passive region was 192 nm. The static current switching with the fabricated switch indicated a large carrier induced refractive index change; up to 14 π phase shift was obtained with 60 mA injection in the SOA. The carrier recovery time of the SOA for obtaining a phase shift of π was estimated to be 250-300 ps. A clear eye pattern was obtained in 2.5 Gbps all-optical wavelength conversion. This is the first all-optical wavelength conversion demonstration with a bandgap-engineered PIC with either selective area growth or quantum-well intermixing techniques.

A low energy plasma based on an electron discharge was investigated for the pre-epi clean of silicon wafers and for plasma enhanced homo and hetero epitaxial growth of Si and SiGe layers. VS were produced in a short, completely dry process sequence consisting of LEPC and LEPECVD only. The wafer/epilayer interface obtained in this process sequence was suitable to grow high quality VS with low surface roughness and dislocation densities. Based on this process and its implementation in a 200/300 mm single wafer cluster tool, a high volume and economical production of VS seems possible.

A TlGaAs/GaAs multiple quantum-well (MQW) structure having four identical well layers was grown on a GaAs (001) substrate by low-temperature molecular-beam epitaxy (MBE) at 190. The (004) X-ray diffraction (XRD) curve of this sample showed satellite peaks up to the 3rd order at least. The measured XRD curve agreed well with the theoretically simulated one with a Tl content of x=7% and a width of 57 for the TlxGa1-xAs well layers. This result indicates that the grown MQW structure has good single-crystalline quality as well as flat and sharp interfaces.

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.

We report the process flow and technological features of Infineons' 75 GHz bipolar technology, which is characterized by a double-poly self-aligned transistor structure and a SiGe base, grown by selective epitaxy. The dependence of the epitaxial deposition on growth conditions and the influence of layout on the growth process is discussed, especially for different kinds of reticles: bipolar-ICs, BICMOS-ICs and discrete semiconductors. Finally, our monitoring concept for the control of the selective SiGe epitaxy is presented and compared with alternative methods of process control.

We studied theoretically and experimentally an InGaAs/InAlAs/InP polarization-insensitive multiple quantum well (MQW) electroabsorption (EA) modulator operating over a very wide wavelength range in 1.55 µm wavelength region. One of the simplest possible potential-tailored quantum well, "pre-biased" quantum well (PBQW) is used to achieve wide-wavelength polarization insensitivity. PBQW is basically a rectangular quantum well with a thin barrier inserted near one edge of well. This thin barrier effectively introduces "pre-bias" to a rectangular quantum well and the same amount of Stark shift is achieved for electron-heavy hole and electron-light hole transition energies. By incorporating tensile strain into PBQW, polarization-insensitive modulation is achieved over 60 nm wavelength range, from 1510 nm to 1570 nm. This MQW-EA modulator plays an important role in wavelength division multiplexing (WDM) transmission and switching systems.

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.

The epitaxial lateral overgrowth (ELO) of GaN with a stripe tungsten (W) mask pattern is performed by hydride vapor phase epitaxy (HVPE) and the crystalline and optical properties are investigated compared with ELO GaN using SiO2 mask by characterizations of X-ray rocking curve (XRC), transmission electron microscopy (TEM) and low temperature cathodoluminescence (CL). A buried ELO structure of the W mask with a smooth surface is successfully obtained. The tilt of c-axis on the W mask in the ELO GaN is not observed, but in the case of the SiO2 mask, c-axis tilts on the mask region at 1 to 10 together with small angle grain boundaries. Half the way from the ELO interface to the surface, the luminescence becomes excitonic over the whole lateral extension region, which indicates the optically high crystalline quality of the material. On the other hand, different kinds of luminescence are observed depending on the position. The difference of these luminescence is caused by the defects and/or impurity incorporation on the mask region due to the tilting of c-axis.

Carbon-doped base InP/InGaAs heterojunction bipolar transistor (HBT) technology for millimeter-wave application is presented. Ultra-high carbon doping of InGaAs layers lattice-matched to InP with hole concentrations in excess of 1 1020 /cm3 has been achieved using a chemical beam epitaxy (CBE). Heavily carbon-doped base InP/InGaAs HBT epi structures were grown and small area, self-aligned HBTs with 1.5 µm emitter finger width were fabricated using triple mesa etching and polyimide planarization techniques. The fabricated small area transistors showed a common-emitter current gain cut-off frequency (fT) as high as 200 GHz. Preliminary device reliability test results showed the potential of the heavily carbon-doped base InP/InGaAs HBT for high performance microwave and millimeter-wave applications. Applications of the InP/InGaAs single heterojunction bipolar transistor (SHBT) and double heterojunction bipolar transistor (DHBT) to a direct-coupled feedback amplifier and a power transistor, respectively, are presented.

SiGe HBTs with doping level inversion, that is, a higher dopant concentration in the base than in the emitter, are realized based on the double-polysilicon self-aligned transistor scheme by means of selective epitaxy performed in a production CVD reactor. The effects of the Ge profile in the base on the transistor performance are explored. The fabricated HBT with a 12-27% graded Ge profile demonstrates a maximum cutoff frequency of 88 GHz, a maximum oscillation frequency of 65 GHz, and an ECL gate delay time of 13.8 ps.

YBa2Cu3Ox films were grown on MgO(100) substrates by liquid phase epitaxy. Their structural and electrical properties were examined. From TEM plan-view images, it is found that the film consists of large grains whose misorientation angles are less than 1. Although the DC critical current density values decrease with increasing the film thickness, the critical current density value of 9. 3105 A/cm2 at 77 K is obtained for a 7 µm-thick film. A microstrip resonator at 10. 8 GHz with a YBCO ground plane shows Q0 values of 14200 at 77 K and 23300 at 40 K, which correspond to surface resistance values of 650 and 400 µΩ, respectively. By using a microstrip line resonator with a Ti/Au ground plane, the critical field of the film at 77 K and 10. 8 GHz is estimated to be 30 Oe. The third-order intercept of the resonator with the Ti/Au ground plane is the input power of +43 dBm and the output power of +30 dBm at 77 K.

Two types of hetero-epitaxial PbZr0. 48Ti0. 52O3 (PZT) capacitors were fabricated by pulsed laser deposition (PLD). One has an Au/PZT/SrRuO3(SRO)/SrTiO3(STO) structure with remanent polarization (Pr) of 32. 1 µC/cm2. The other has an Au/PZT/La-doped STO (La: STO) structure with Pr of 9. 6 to 13. 5 µC/cm2. X-ray diffraction patterns show that only the (00l) planes of the PZT and SRO are parallel to the substrate surface for the PZT/SRO/STO structure, however, a (111) plane of the PZT is observed, in addition to the (00l) planes, for the PZT/La: STO structure. High resolution-transmission electron microscope (HR-TEM) images show that the PZT/SRO interface is clean and coherent. However, spherical shape contrast with radius about 5 nm is observed at the PZT/La: STO interface. Diffusion of La and/or the contaminated surface of the La: STO substrate is thought to cause the differences in the PZT orientations and the interfaces, affecting the electrical characteristics of the capacitors.

We propose an InGaAlAs waveguide p-i-n photodiode (WG-PD) with a thick symmetric double-core for surface-hybrid integration onto optical platforms, which can be applied to low cost optical modules for access networks. The waveguide structure is designed to efficiently couple to flat-ended single mode fibers while maintaining low-voltage (less than 2 V) operation. Crystal growth conditions and a passivation technique are also investigated for obtaining high responsivity, low dark current and highly reliable operation. Fiber-coupled responsivity as high as 0.95 A/W, at a 1.3-µm wavelength, and vertical coupling tolerance as wide as 2.6 µm are demonstrated for a dispersion-shifted fiber (DSF) coupling at an operating voltage of 2 V. Dark current is as low as 300 pA at 25 and 12 nA at 100. A temperature accelerated aging test is performed to show the feasibility of using the WG-PD in long-term practical applications.

We have developed the Epi-Base SATURN process as a silicon bipolar process technology which can be applied to optical transmission LSIs. This process technology, to which low temperature selective epitaxial growth technology is applied, is based on the SATURN process. By performing selective epitaxial growth for base formation in 2 steps, transistors with a 40GHz maximum cut-off frequency have been fabricated. In circuit simulation based on SPICE parameters of transistors, the target performance required for 2.4 Gbit/s optical interface LSIs has been achieved.