Yoshifumi Amemiya

High‐sensitivity InGaAsP/InP phototransistors

InGaAsP/InP phototransistors have been fabricated using the liquid phase epitaxy technique. In spite of the early stage of development, the fabricated detectors exhibited a current gain of more than 103 and rise time of about 50 nsec. With further development, InGaAsP/InP phototransistors will become promising detectors for optical communication systems in the 1.0–1.7‐μm spectral region.

Measurement of Diffusion Coefficient and Surface Recombination Velocity for p-InGaAsP Grown on InP

Surface recombination velocity S2 and diffusion coefficient D2 of the minority carrier in p-InxGa1-xAsyP1-y (0.65<x<0.74, 0.61<y<0.78) on InP substrate were measured by two independent experiments; a laser-scan experiment on the beveled surface of the sample and a response speed experiment of the photodiode. The two independent experiments were analyzed simultaneously to obtain D2 and S2. The obtained S2 is 3-5×104 cm/s which is about one order of magnitude greater than that on n-InP and about two orders of magnitude smaller than that on GaAs. The diffusion coefficient of the minority carrier in the p-InGaAsP layer D2 is about the same as that of the majority carrier. The obtained D2 is 2-3 cm2/s.

Effect of Substrate Surface on Alignment of Liquid Crystal Molecules

Investigations were made of tilt angles of the molecular long axis in a liquid crystal layer sandwiched between two substrates, which were prepared by evaporating silicon at oblique incidence. Measurements of the dependence on the incident angle were carried out, which showed that the tilt angles varied from 3° to 28.4° for the incident angles ranging from 67° to 86°. Observations of the deposited film surfaces by use of electron microscopy revealed that they had a sawtooth-like structure whose shape also depended on the incident angle. It was suggested that the tilt angle was strongly affected by surface structures of the substrates.

A new InGaAsP/InP dual‐wavelength LED

A new dual‐wavelength light‐emitting diode (LED) emitting near 1.2 and 1.3 μm has been fabricated. The differential efficiencies of the two outputs were 0.36 and 0.88%, respectively. The intensities of these optical outputs can be controlled independently. The optical cross talk between the two wavelengths was −10 and −16 dB at 1.15 and 1.35 μm, respectively. This device is useful for wavelength‐multiplexed optical communication systems.

Hot photo-carrier and hot electron effects in p-n junctions

Abstract When a p - n junction of semiconductor (with bandgap energy E g ) is illuminated by light beam (with photon energy hv ) in the condition of E g > hv , such as in Ge p - n junction illuminated by CO 2 laser beam, an electromotive force (emf) was induced between the terminals of the p - n junction, which indicated the opposite polarity to the ordinary photovoltaic effect like a solar cell. Such an anomalous photovoltaic phenomenon was explained by an optically excited hot carrier effect, through the following experiment with electrical excitation. Using a rod of n - or p -type Ge with a p - n junction at the surface of its center and an ohmic contact at each terminal of the rod, the same kind of phenomena was observed when electric field is applied along the length of the rod. The perpendicularly induced voltage or current had the same polarity instead of the reverse change of the applied electric field, and increases with increasing the applied field strength. The perpendicularly induced emf was caused by warm or hot carriers crossing the potential barrier of the p - n junction, which is very sensitive to the departure from thermally equilibrium velocity distribution of carriers.

Calculation of Ignition Noise Level Caused by Plug Gap Breakdown

This paper describes the electromagnetic ignition noise caused by the gap breakdown of a plug. An ignition current which flows through the plug body is analyzed by making use of a Rompeweizel eizel formula for the spark resistance. From the analyses, effects of gap breakdown properties on the ignition currents are elucidated. A method to calculate the ignition current level from the relevant plug dimensions and the gap breakdown voltage is given, and the results are confirmed experimentally.

InGaAsP/InP photodiodes antireflectively coated with InP native oxide

Usefulness of the anodically grown native oxide film in InP surface is demonstrated as an antireflection coating of InGaAsP/InP DH photodiodes. The reflection of the InP is 30 percent, while that with coating is 2.8 percent in the wavelength region considered. The quantum efficiencies of 64 percent for the uncoated diode and 82 percent for the coated one were obtained. Some important optical properties of the anodically oxidized film are also measured.

Ellipsometric and infrared spectroscopic studies of oxide film on GaAs surface

Abstract By ellipsometries and infrared spectroscopies the native oxide films, anodically grown on GaAs by AGW, which are composed of Ga2O3 and As2O3 with thermal stability under 300°C and a transition layer of less than 300 A at the interface, are studied in detail. The reflectance spectra of the film in the 0.4–10 μm range, which are electrically controlled precisely, and profitable for antireflcction coating, arc studied.

Critical Surface Tension of Silicon Films and Aligning Properties of Nematic MBBA Molecules

A method for estimating the critical surface tension of obliquely deposited silicon films is presented. It is based on the measurement of equilibrium contact angles of sessile drops of test liquids with different surface tensions. The critical surface tension calculated by the equation 1+\frac{\cos\theta_{\text{a}}}{r_{\text{w}}}=\frac{2}{\gamma_{\text{L}}}(√γLdγCd+√γLpγCp) is 48.4 dyn/cm. The aligning properties of nematic MBBA molecules are also discussed.

The performance of the dipole array applicator for radiofrequency hyperthermia

Hyperthermia is presently drawing attention in the field of cancer therapy. This paper describes the results of a heating experiment at 40 MHz using the dipole array applicator proposed by the authors as a means to realize deep heating in the human body. As the first step, numerical calculations are made of the electric field distribution in the object phantom (simulating human body), indicating that the electric field and consequently the heat generation is almost uniform in the phantom. Then a phantom is constructed in which the circulation of a saline solution can be varied depending on the location, and the heating experiment was performed. When the saline solution is not circulated, the temperature rise is almost uniform within the phantom, as is expected from the calculation of electric field distribution. When the saline solution is circulated, the temperature rise is high in the area of smaller circulation, which simulates the cancer. As an example, for 30-minute heating by 1.6 kW, the temperature-rise is 5°C.