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Ohmic contacts are formed on the epitaxial n-GaN film by the electron beam evaporation of Ti/Al and their rapid thermal alloying with device separation by a fairly fast Electron Cyclotron Resonance (ECR) plasma etching. The etched surface has a poor ohmic contact with a typical contact resistance of 8.1 × 10 - 3 Ω.cm 2 , while the as-received and rinsed surface has a better contact with a lower contact resistance of 7.5 × 10 - 6 Ω.cm 2 . The resistivity of the film is determined as a function of the temperature, in good agreement with the numerical analyses. The ohmic characteristics are evaluated by the 1/f noise measurements. Low ohmic contacts give the typical 1/f noise characteristics which increase with the square of the sample current 1, while higher ohmic contacts give a linear noise power dependence on the sample current 1. We are able to evaluate, therefore, the ohmicity of the electrodes most sensitively from the 1/f noise measurements. Assuming the relevant total electron number between the electrodes, the Hooge parameter is estimated as α H = 5.3 x 10 - 6 at room temperature, in qualitative agreement with the cross correlational 1/f noise model.

We fabricated the first ultrafast active transmission lines with low dielectric constant (low-k) polyimide integrated with ultrafast photoconductive switches formed by the nano-anodization process. Electrical pulses as short as 290 fs were measured on this transmission line by an electrooptic sampling system based on a femtosecond laser. P-n junctions were inserted in the transmission line to control dispersion in lines, and low-k polyimide was introduced to reduce dielectric and radiation losses.

Experiments were carried out for the n-channel devices, processed in a 0.3 µm spacer less complementary metal–oxide–semiconductor technology. Random-telegraph-signal measurements were performed for the constant gate voltage. It is supposed that electron concentration in the channel decreases from the source to the drain contact. Lateral component of the electric field is inhomogeneous in the channel and it has a minimum value near the source and reaching the maximum value near the drain electrode. Drain current is given by two components – diffusion and drift ones. Diffusion current component is independent on the x-coordinate and it is equal to the drift current component for the low electric field. The model explaining the experimentally observed capture time constant dependence on the lateral electric field and the trap position is given. From the dependence of the capture time constant τc on the drain current could be calculated longitudinal coordinate of the trap position.

Current collapse has been studied in unpassivated and SiN-passivated AlGaN/GaN heterostructure devices grown on a sapphire substrate by means of low-frequency-noise measurement at low temperatures, indicating this to be the most sensitive and powerful tool for assigning the deep levels in these complex and complicated structures. Generation–recombination (G–R) noise was explicitly observed in the unpassivated AlGaN/GaN heterostructure at low temperatures (T = 50–110 K) with the activation energy of 47 meV. This level was found to be dramatically decreased by the SiN passivation, from −205 dBA Hz−1/2 down to −217 dBA Hz−1/2, the current collapse being cured at the same time. With the SiN passivation a further G–R noise corresponding to the deeper traps of 131 and 235 meV became comparable to that corresponding to 47 meV.

Some serious accidents caused by declines in arousal level, such as traffic accidents and mechanical control mistakes, have become issues of social concern. The physiological index obtained by human body measurement is expected to offer a leading tool for evaluating arousal level as an objective indicator. In this study, declines in temporal arousal levels were evaluated by nasal skin temperature. As arousal level declines, sympathetic nervous activity is decreased and blood flow in peripheral vessels is increased. Since peripheral vessels exist just under the skin on the fingers and nose, the psychophysiological state can be judged from the displacement of skin temperature caused by changing blood flow volume. Declining arousal level is expected to be observable as a temperature rise in peripheral parts of the body. The objective of this experiment was to obtain assessment criteria for judging declines in arousal level by nasal skin temperature using the alpha attenuation coefficient (AAC) of electroencephalography (EEG) as a reference benchmark. Furthermore, a psychophysical index of sleepiness was also measured using a visual analogue scale (VAS). Correlations between nasal skin temperature index and EEG index were analyzed. AAC and maximum displacement of nasal skin temperature displayed a clear negative correlation, with a correlation coefficient of −0.55.

A 250 MHz Li2B4O7 surface acoustic wave (SAW) filter was successfully designed using a newly developed program for double-mode SAW (DMS) filters. The elastic, piezoelectric and dielectric constants of Li2B4O7 grown by the resistance-furnace heating Czochralski method were measured precisely to determine the accurete phase velocity and the electromechanical coupling coefficient of SAW. The mode coupling coefficients were determined as a function of the electrode thickness as well. These coefficients were introduced in the simulation program, and the SAW filter was designed. The DMS filter fabricated in this study had almost the same characteristics as those expected from the design.

Photoluminescence (PL) analysis on n-In0.52Al0.48As/In0.8Ga0.2As/In0.52Al0.48As/InP pseudomorphic heterostructures grown by molecular beam epitaxy has been carried out to investigate the critical layer thickness. Crystal quality degradation is followed by the relaxation of the lattice-mismatched layer. The critical layer thickness for this material system that is measured by PL is found to agree with the value from the energy balance model.

Voltage noise spectrum densities of quarter-micron filaments made by GaAs, InP and heterostructures are measured in detail as a function of decreasing temperature to 10 K, and the Hooge noise parameter αH of each device is precisely determined at each temperature. Focused ion beam (FIB) implanted n-GaAs has the smallest αH of 1.0×10-8 at 60 K, decreasing from 2×10-6 at room temperature. The derived value of αH is the smallest one ever reported for compound semiconductor devices, and compares favorably with that expected from quantum 1/f noise theory. FIB-implanted n-InP has the smallest αH of about 1×10-7 at 50 K. The αH of a molecular beam epitaxially (MBE) grown In0.8Ga0.2As heterostructure depends on µpo between 1 to 10 m2/V·s, realizing 1/f noise in the cross section of optical phonon scattering.

The stability of a linearly pinched cylindrical plasma is investigated in the absence of an external magnetic field. The theory is based on the magnetohydrodynamic equations of motion and the particle conservation combined with Maxwell's equations. The dispersion relation of the instability and the explicit dependence of the wave parameters on the field are obtained by linearizing the equations for axially symmetrical harmonic perturbation. Numerical results on the threshold show that the axial current required to cause the instability is inversely proportional to the electric field, and that the oscillation frequency increases linearly with the electric field while the wave number remains approximately constant. The spatial growth rate and the phase velocity of the instability are also obtained as a function of the field strength.

An Experimental investigation is made on the sausage-shaped instability in an impact ionized plasma of n-InSb. Sinusoidal voltage oscillations are observed after complete confinement of a pinch without an external magnetic field, and the frequency is measured as a function of a sample current. Oscillation frequencies and currents at a threshold are obtained as a function of an applied electric field and compared with the dispersion relation theoretically obtained. Theoretical considerations are in good agreement with the experimental results on axial magnetic field stabilization of the oscillations.

Fabrication processes to make an excellent p + n-junction on bulk n-InP by 24Mg-ion implantation are described. The leakage-current density through a junction was less than 10-7 A/cm2 with a rectification ratio larger than 106 at a bias voltage of - 1 V and a junction breakdown voltage below - 60 V without any guardring structure. A 2.0-mm long junction waveguide was used to control the long-wavelength (λ=1.135 µm) light with an extinction of 8.6 dB at 10 V.

A self-aligned-gate inversion-mode InP metal-insulator-semiconductor field-effect transistor (MISFET) was successfully fabricated by using plasma-assisted chemical-vapor-deposited Si3N4 film both as the insulator and as the capping layer for the annealing process. A channel mobility of 2700 cm2/Vs and a transconductance of 55 mS/mm at a gate voltage of 4 V were achieved with a reasonably low source-drain leakage current.