To increase the affinities of aptamers for their targets, we designed an aptamer dimer for thrombin and VEGF. This design is based on the avidity of the antibody, which enables the aptamer to connect easily since it is a single-strand nucleic acid. In this study, we connected a 15-mer thrombin-binding aptamer with a 29-mer thrombin-binding aptamer. Each aptamer recognizes a different part of the thrombin molecule, and the aptamer dimer has a Kd value which is 1/10 of that of the monomers from which it is composed. Also, the designed aptamer dimer has higher inhibitory activity than the reported (15-mer) thrombin-inhibiting aptamer. Additionally, we connected together two identical aptamers against vascular endothelial growth factor (VEGF165), which is a homodimeric protein. As in the case of the anti-thrombin aptamer, the dimeric anti-VEGF aptamer had a much lower Kd value than that of the monomer. This study demonstrated that the dimerization of aptamers effectively improves the affinities of those aptamers for their targets.

A GaInP(N)/GaAs( p) heterojunction bipolar transistor was fabricated by metalorganic chemical vapor deposition (MOCVD) for the first time. The common-emitter current gain exceeded 200 at a current density around 10 A/cm2 and the offset voltage was as small as 50 mV. Thermionic emission theory indicates that the conduction-band discontinuity (ΔEc) at GaInP/GaAs heterointerface is as small as 30 meV at room temperature and this value was more than 160 meV smaller than 0.19–0.22 eV obtained by the C-V profile method. The band-gap energy for MOCVD-grown GaInP was 60 meV smaller than the intrinsic band-gap energy (1.91 eV), but this value is too small to explain the difference between the present ΔEc value and the previously reported ΔEc value.

Origin of a nonradiative center in AlGaAs grown by molecular-beam epitaxy was investigated by secondary ion mass spectroscopy and deep-level transient spectroscopy, from the change of photoluminescence intensity with anneal treatment, and from its comparison with GaAs. Aluminum-oxygen complex is a most probable defect which acts as a nonradiative center in AlGaAs, and the oxygen would evaporate as Al2O from the surface, which would be a reason why the photoluminescence intensity increases under higher substrate temperature and lower V/III flux ratio. The electron-trap level at 0.76 eV from the conduction band would be the recombination center, and the photoluminescence intensity is inversely proportional to the trap concentration.

Using GaAs/AlGaAs/InAs/AlGaAs/GaAs tunneling diodes, we have investigated the resonant tunneling current through InAs wetting layers and self-assembled quantum dots obtained from the Stranski-Krastanow growth mode. For InAs layers both with and without the quantum dots, resonant tunneling current through two-dimensional (2D) electronic states in the wetting layers is observed. From this observation, we can determine the 2D ground state energy. On the other hand, current peaks due to resonant tunneling from three-dimensional (3D) electronic states in the emitter to zero-dimensional (0D) states in the quantum dots are observed only for the case of an InAs layer with the quantum dots.

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