Toru Kurabayashi

GaAs TUNNETT diodes oscillating at 430-655 GHz in CW fundamental mode

GaAs TUNNET diodes with 75-nm thick undoped transit-time layer and 14-nm thick n/sup +/ electric-field-inducing layer were fabricated with molecular layer epitaxy. They were oscillating in fundamental-mode metal rectangular resonant cavities of WR-1.5 (0.381 /spl times/ 0.191 mm) and WR-1.2 (0.305 /spl times/ 0.152 mm) types. Continuous wave generation of -53 dBm to -49 dBm, in the frequency range of 430-510GHz, at the bias current from 500 to 560 mA was obtained in the WR-1.5 cavity. In the WR-1.2 cavity, CW generation in the range of 571-655 GHz was obtained with the bias current changing from 460 to 540 mA. Output power was -61dBm at 655 GHz. Frequency range of CW fundamental-mode TUNNETT diodes fabricated with molecular layer epitaxy extends from 60 GHz (+13 dBm) to 655 GHz.

Sub-terahertz imaging of a painted steel

Terahertz spectroscopy of paint films has been studied in a range from 0.1 to 18 THz. The paint layers in actual use showed strong-absorption at higher frequency range, however they showed transparent characteristics in sub-THz range. Hence, sub-terahertz imaging of a painted steel plate as a method of nondestructive inspection was performed using a wave ranging from 100 to 200 GHz. An invisible rusty area covered with multiple paint layers on steel in actual use was effectively detected by power-reflection imaging.

Self-limiting growth of GaAs molecular layer epitaxy using triethyl-gallium (TEG) and AsH3

The surface reaction mechanism of GaAs MLE using a triethyl-gallium (TEG)-AsH 3 system was studied by varying the sequence of gas injection of TEG and AsH 3 . The decomposition of TEG was found to be enhanced on the Ga-terminated (001)-oriented GaAs surface. The average lifetime of AsH x (x = 0, 1, 2) formed by the AsH 3 supply was 8 s, and the lifetime of the ethyl group of the ethyl-gallium compound formed by the TEG supply was about 2 s. The gas supply sequence was chosen to be within the two lifetimes, and the self-limiting growth at the monolayer was achieved in the TEG pressure region of more than 5.3 × 10 -3 Pa at a temperature of 270°C.

Identification of textile fiber by terahertz spectroscopy

We developed a novel differentiation technique for most textile fibers using terahertz (THz) transmittance spectroscopy. As demonstrations, several kinds of plant-derived fibers, animal fibers, and artificial fibers were milled at 77K, and were examined by THz spectroscopy in the range from 0.5 to 6.2 THz. Absorption spectra of a majority of textile fibers are distinguishable by THz spectroscopy, even for fibers in the same category or species. The advantage of this technique is its sensitivity to the structural differences of the textile fibers, even if they consist largely of the same components.

Sub-terahertz imaging for construction materials

Sub-terahertz imaging for construction materials has been performed using room-temperature operating oscillators. Invisible defects in woods, and mixed foreign bodies and cracks in concrete were detected effectively by power transmission imaging. In addition, rusty area covered with paint on the steel was distinguished by power reflection imaging. So, Sub-terahertz imaging is one of the promising tools for the safe structural engineering.

Significance of terahertz spectrometry for textile article of wool

We present a novel differentiation technique for several kinds of textile fabric using terahertz (THz) transmittance spectroscopy. Our goal is to establish a new method for identification of each of wools from their animal species, as a simple, rapid and reliable method to confront fake textile problem in the market. As demonstrations, several kinds of fabrics were milled at 77K, and were examined by using GaP THz spectrometer in the measurement range from 0.5 to 6.0 THz. The absorption spectra of wool showed quite different spectra from plant-derived fibers and synthetic fibers. Furthermore, the spectra of pure wools showed different transmittance spectra between goat-wool and sheep-wool, in addition among the species of sheep.

Doping method for GaAs molecular-layer epitaxy by adsorption control of impurity precursor

The doping mechanism of Se and Te in GaAs molecular-layer epitaxy (MLE) was examined by the timing of supply of the impurity precursor on each orientation of the substrate. On (001) GaAs, the impurity incorporation on the growing surface may be prevented by AsH x (x = 0, 1, 2, 3) adsorbed during the AsH 3 supply, and is apt to be promoted on a Ga-terminated surface. For each orientation of the substrate, the doping characteristics differ noticeably. On the (111)A surface, Te is incorporated at the lowest temperature, while it is incorporated at the highest temperature on (111)B. It was clarified that control of the adsorption of impurity precursor is an essential factor in the precise control of doping in MLE.