Susceptibility to the development of asthma and other atopic diseases is known to be associated with genetic components, and several candidate genes have been reported to be linked to atopy in Caucasian populations. We conducted a study of linkage between asthma and markers on chromosomes 5q31-q33 and 11q13 in 68 Japanese families (306 members) by affected sib-pair analysis. Families for the linkage study were ascertained through asthmatic children visiting the allergy clinic. The results provide supportive evidence for linkage between asthma and gene markers in or near the interleukin-4 (IL-4) gene, the IL-9 gene, and D5S393 on chromosome 5q31-q33 (p = 0.0013, p = 0.018, and p = 0.0077, respectively). Linkage between atopic phenotype and these genetic markers was also suggested (p = 0.006, p = 0.01, and p < 0.0001 for atopy, respectively). However, we failed to find evidence for linkage of asthma or atopy to the IgE high-affinity receptor gene on 11q13 (p > 0.1). These findings indicate that beyond ethnicity, there are specific loci that contribute to susceptibility to atopy on chromosome 5q31-q33. In addition, our findings suggest that loci on chromosome 5q31-q33 are linked to the development of asthma in childhood.

The thermal annealing effect on the photoluminescence (PL) characteristics of GaInNAs/GaAs quantum wells (QWs) grown by chemical beam epitaxy (CBE) using radical nitrogen is presented. The room-temperature PL peak intensity of GaInNAs/GaAs QWs increased about 70 times and the linewidth of PL spectra decreased after annealing at 675°C for 30 seconds. The blue shift of the PL peak wavelength of GaInNAs/GaAs QWs and GaNAs/GaAs QWs, due to the structural change of QWs was observed. It was found that the blue shift was caused by In–Ga interdiffusion rather than nitrogen atom diffusion. The interdiffusion caused by defects is thought to reduce the number of non radiative centers, resulting in the improvement of PL characteristics. The optimum annealing temperature depends on the composition.

We report on the lasing characteristics of low-threshold long-wavelength GaInNAs double quantum well (DQW) lasers grown by metalorganic chemical vapor deposition (MOCVD). We have achieved a threshold current density of 450 A/cm2 for a 1.28-µm-emitting laser. This is the lowest value for 1.3-µm-range GaInNAs lasers grown by MOCVD. We also observed high characteristic temperatures (T 0) of 210 K and 130 K for 1.25 µm and 1.28 µm lasers, respectively. In addition, we investigated the gradual change in lasing characteristics under pulsed operation. The blue shift of an emission wavelength and a threshold current reduction were observed, which is similar to that observed in the thermal annealing of GaInNAs.

This paper experimentally demonstrates the strong enhancement of light extraction efficiency in two-dimensionally arranged microcolumns. They were designed like a honeycomb photonic crystal and fabricated into GaInAsP-InP wafers by using the inductively coupled plasma etching. For the laterally directed light passing through the microcolumns, peculiar transmission characteristics were observed, which could be explained by the Bragg reflection theory, namely, the photonic bandgap (PBG). The measurement of spontaneous lifetime showed that the internal efficiency in the microcolumns was reduced by the surface recombination at sidewalls. In contrast, the light extraction efficiency evaluated from the measured photoluminescence intensity, and the internal efficiency was more than ten times that for a planar wafer. This was thought to be due to the expanded escape cone of internal light by the low effective refractive index, and also due to the strong diffraction and scattering of laterally directed light, which corresponds to the second-order Bragg condition. Such effects are expected not only in photonic crystals but also in some disordered structures. We expect this structure to allow a high-efficiency light-emitting diode (LED), since electronic elements needed for current injection devices can be added independently of the effects.

We investigated the doping and electrical characteristics of p-type GaInNAs for use in a p-contact layer and in the p-distributed Bragg reflectors ( p-DBRs) of surface emitting lasers. Beryllium doping was applied to GaInNAs grown by solid source molecular beam epitaxy with the nitrogen radical. The doping efficiency for the lattice-matched GaInNAs is similar to that of the GaAs, and a slight deterioration in hole mobility indicates the alloy scattering of the GaInNAs.

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We report a feasibility study of a terahertz imaging system with resonant tunneling diodes (RTDs) that oscillate at 0.30 THz. A pair of RTDs acted as an emitter and a detector in the system. Terahertz reflection images of opaque samples were acquired with our RTD imaging system. A spatial resolution of 1 mm, which is equal to the wavelength of the RTD emitter, was achieved. The signal-to-noise ratio (SNR) of the reflection image was improved by 6 dB by using polarization optics that reduced interference effects. Additionally, the coherence of the RTD enabled a depth resolution of less than 3 µm to be achieved by an interferometric technique. Thus, RTDs are an attractive candidate for use in small THz imaging systems.