A carbon nanotube mat (CNT mat) with long (~1 mm) multi-walled carbon nanotubes (MWCNTs) was used to process MWCNT/epoxy composites at high concentrations (4.4 and 10.0 wt.%) of MWCNTs by a simple method without the use of a solvent. The CNT mat circumvents several cumbersome processing steps, including the dispersion of CNTs in a solvent. Two different resin-impregnation processing methods were explored. The processing steps were chosen to prepare composite samples based on the performance of the composites and the simplicity of the processing techniques. Scanning electron microscopy (SEM) was used to examine the microstructures of the CNT mat and its composites. The mechanical and electrical properties were tested. The tensile strengths of the composites with 10.0 wt.% MWCNTs were increased by 17% to 90% when compared to that of neat epoxy samples. The electrical conductivity of the composite is 36.1 S/cm. 4.4 wt.%-MWCNT composites show very large strain valuesupon fracturing (> 15 %), and their electrical conductivity is 14.9 S/cm. These results show that CNT mat/epoxy composites can be used as flexible electrodes and as a matrix system for advanced fiber composites.

No abstract

The grating coupled GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) are integrated onto Si substrates using metal wafer bonding and epitaxial lift-off process. The 1 μm depth of hexagonal hole structure of grating was formed. The energy-dispersive x-ray spectroscopy results confirmed that the grating coupled QWIP is successfully mounted on an Si substrate. By evaluating the Raman spectra, PL, and surface roughness of bonded QWIP samples, the authors found that the grating does not induce any change in the optical or structural characteristics of actual QWIP layers. The dark current–voltage characteristics show a nearly identical dark current level between grating coupled QWIP and nongrating QWIP. The photocurrent spectrum shows that the peak photocurrent intensity of grating coupled QWIP is about 16 times higher than that of nongrating QWIP. This indicates that the grating effectively contributes to an increase in the light absorption of QWIP, showing large room for improvement of QWIP performance by further optimization of a grating structure.

A method for the dry thermal oxidation of a strained SiGe layer is proposed. By oxidation of a graded Si1−xGex layer, the effect of Ge pileup was significantly reduced and the undesirable strain relaxation by defect formation is prohibited. After oxidation, the oxidized SiGe layer was homogenized by postannealing process, and thereby a SiO2/SiGe interface with good structural properties was obtained. During postannealing, the homogenization was significantly enhanced by strain-induced diffusion, and it was clearly proved by the uphill diffusion. This result can propose an alternative oxidation method of strained SiGe/Si heterostructures.

InAlGaAs tunnel diodes, lattice-matched to InP and grown by molecular beam epitaxy, are demonstrated with peak tunneling current densities exceeding 1200 A/cm2. This was achieved by a 20 °C reduction in growth temperature for the p-type tunnel diode layers, resulting in up to two orders of magnitude improvement in the peak tunneling current density. Secondary ion mass spectrometry measurements reveal that the lower growth temperature reduces unwanted segregation of p-type Be dopants, improving dopant incorporation within the active tunnel diode layers. The diodes are transparent to wavelengths above 1000 nm and are compatible with the bottom junctions of InP-based multi-junction solar cells and with InP-based photonic power converters operating in the telecommunication O- and C-bands. When incorporated into a dual-junction photonic power converter test structure, measurements under 1319-nm laser illumination demonstrate integrated tunnel diode operation, enabling a halving of the short-circuit current and doubling of the open-circuit voltage as compared to a single junction reference device.