We developed the self-organization technique of two-dimensional nanoarrays of Ge quantum dots (QDs) epitaxially grown on Si substrates using ultrathin SiO2 films, which was featured by the ability to self-repair of the array defects. Nanometer-sized voids (nanovoids) were hexagonally patterned on ultrathin SiO2 films by transcription of the pattern of block copolymer films using selective etching method. The nanovoids worked as nucleation sites for QD growth by Ge deposition onto the patterned ultrathin SiO2 films to form the regularly arranged epitaxial QDs. There were some deficiency sites in the nanovoid arrays created by selective etching. These nanovoid deficiencies, which result in QD nanoarray defects, self-repaired during Ge deposition through the reaction of Ge atoms with the SiO2 films at the nanovoid deficiency sites. The resulting epitaxial QD nanoarrays were elastically strain-relaxed without misfit dislocations and of uniform size owing to the regularly arranged nanovoids with ultrasmall size.
Intensity oscillations of reflection high-energy electron diffraction are observed during epitaxial growth of a C60 layer on GaAs substrates. The frequencies of the oscillations coincide well with the growth rates of C60 layers, suggesting that C60 layers grow by layer-by-layer growth mode. C60 uniformly doped and delta-doped GaAs layers are grown by migration enhanced epitaxy method. C60 uniformly doped GaAs layers show highly resistive characteristics, suggesting that C60 molecules cannot be decomposed into isolated C atoms. Electrochemical capacitance-voltage profiles of C60 delta-doped GaAs layers suggest that C60 molecules in GaAs lattice produce deep electron traps which can be charged or discharged by applied electrical fields.
ZnO based oxide semiconductors have attracted much attention for light emitting devices and photo detectors in short visible wavelength due to its unique properties such as a wide direct bandgap of 3.3 eV and a large exciton binding energy of 60 meV. p-type MgxZn1-xO (0 ≤ x ≤ 0.2) has been required for realizing a light emitting device in ZnO based heterostructure or as an active layer in UV photodetectors. We present here a demonstration of a photodetection in MgxZn1-xO Schottky photodetectors with surface treatment on MgxZn1-xO film and a systematic analysis with the Mg content of the formation and concentration of deep levels found throughout the lower half of the bandgap of MgxZn1-xO by deep level optical spectroscopy (DLOS).
Oxide semiconductors are promising “green materials” suitable for unique functional devices in the next generation. Precise surface control during the growth, similarly to other semiconductors, is a key for their property control as well as their high-quality layers and interfaces. Our recent interest has been focused on gallium oxide (Ga2O3), due to its wide band gap and precedent development of its β-phase bulk substrates. Here we report successful fabrication of deep ultraviolet photo-detectors with thermal treatment of the substrate surface and achievements of step-flow growths of Ga2O3and (AlGa)2O3. By applying the mist vapor-phase growth technology, which we have developed as a safe and simple growth method for oxides, the formation of “green materials” can be supported by “green technology”. Now our research stage is limited to heteroepitaxial growth on sapphire substrates, but the results indicated the growth of highly-crystalline corundum-structured α-phase Ga2O3with confining the lattice-mismatching-induced defects at the epilayer/substrate interface. This may lead to evolution of corundum-structured multifunctional oxide semiconductors.
This paper describes group-III nitride (III-N)/SiC heterointerface and its device applications. Heteroepitaxial growth of III-N on SiC opens new opportunity of SiC-based heterojunction devices such as heterojunction bipolar transistors (HBTs). The authors developed growth methods to grow high-quality III-N on SiC by molecular-beam epitaxy. Fabricated GaN/SiC heterojunction exhibited type-II band-lineup. By using AlN/GaN short period superlattice as a quasi AlGaN alloy, the authors successfully controlled the band-lineup to be type-I and demonstrated common-emitter-mode operation of III-N/SiC HBTs.
Diamond/III-V nitride semiconductor heterostructure appears promising not only for high-efficiency deep-UV light emitting diodes (LEDs) but also for high output power field-effect transistors (FETs). However, diamond has a diamond crystal structure, while III-V nitride semiconductors have a wurtzite crystal structure. Due to the deference in the crystal structures, single-crystal III-V nitride growth on diamond substrate was difficult. In this study, we obtained the single-crystal aluminum nitride (AlN) (0001) layers on diamond substrates by using (111) diamond surface orientation and preventing the formation of the interface layer. Then, we revealed the heteroepitaxial growth mechanism and proposed an atomic arrangement model at the diamond/AlN heterointerface. Furthermore, we demonstrated a p-type diamond/n-type AlN heterojunction diode and successfully observed band-edge emission from diamond. In addition, an AlGaN/GaN heterostructure with two-dimensional electron gas (2DEG) was grown on diamond (111) using the single-crystal AlN buffer layer.
An atmospheric-pressure argon (Ar) plasma jet was applied to disinfect against Escherichia coli (E. coli). The Ar plasma jet was generated at a frequency of 9 kHz, applied voltage of 10 kV, and Ar gas flow rate of 10 L/min at atmospheric-pressure. The length and the diameter of the Ar plasma jet was approximately 3 cm and 6 mm, respectively. E. coli seeded on an agar plate in a Petri dish was exposed to the Ar plasma jet. E. coli was disinfected by Ar plasma jetexposure for 2 s. The results of temperature and emission measurements for the Ar plasma jet indicated disinfection effects were neither due to the heat nor due to the light from the Ar plasma jet. The results of scanning electron microscopy (SEM) observation showed the E. coli cells deformed and faded after the Ar plasma jet exposure. Therefore, the disinfection of E. coli was probably due to the destruction of cell wall and cell membrane caused by the collision of charged particles such as Ar ions, electrons and metastable excited atoms and molecules.
A quartz crystal oscillation unit was modified by immobilizing single-stranded DNA (ssDNA) on its surface and incorporated into a quartz crystal microbalance (QCM) system as a biosensor for the purpose of detecting specific fungus. The ssDNA having base sequence specific to 28S rDNA D2 domain of Omphalotus guepiniformis, which is a toadstool that often causes a false appetite resulting in poisoning, was immobilized on a gold electrode of the quartz crystal unit, and used as a probe for detection of complementary target DNA. The detection of target DNA was carried out by monitoring the decrease in oscillation frequency due to mass increase on the surface of the quartz crystal unit, which accompanied the hybridization of the probe and target DNAs to form double strands. In advance, the DNA hybridization was examined by the QCM method with a synthesized oligonucleotide (25 bases) having same sequence as that specific to O. guepiniformis 28S rDNA D2 domain, and the hybridization efficiency was estimated to be 97-101%. Subsequently, DNA was extracted from a minute piece (0.1 g) of O. guepiniformis fruit body, and the 28S rDNA D2 fragment was amplified by polymerase chain reaction (PCR). It was confirmed that fragment (308 bases) of the PCR product was detected by the QCM measurement which showed a marked decrease in oscillation frequency. In addition, the 28S rDNA D2 fragment of O. guepiniformis was detected for a mixture with those of Lentinus edodes and Pleurotus ostreatus. This result suggests that the DNA-modified quartz crystal unit can be applied to the detection of a specific toadstool included in leftover foods or vomited matter.