Munecazu Tacano

Highly-sensitive Hall element with quantum-well superlattice structures

Abstract A highly-sensitive Hall element made of modulation-doped AlAs/GaAs superlattice structures has been developed. By inserting an undoped-GaAs quantum-well with a thickness of 2.5 nm into the AlAs interface barrier neighboring the GaAs buffer, we obtained an enhancement of the magnetic sensitivity at high DC electric field. The maximum sensitivity was 18 V/T, more than three times that of the conventional GaAs Hall elements.

Comparison of 1/ƒ noise of AlGaAs/GaAs HEMTs and GaAs MESFETs

Abstract The drain voltage noise of commercial AlGaAs/GaAs HEMTs shows typical ƒ −1.0 noise characteristics with a Hooge noise parameter of about 6 × 10−5, while that of conventional GaAs MESFETs has a large GR noise bulge at about 15 Hz. The noise levels of the HEMT are smaller than those of the MESFET by 19 dB Hz−0.5 at the same bias conditions, manifesting the advantage of HEMT as a low-noise device.

Correlation analysis on alpha attenuation and nasal skin temperature

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.

Highly sensitive split-contact magnetoresistor with AlAs/GaAs superlattice structures

A class of split-contact magnetoresistors made of a modulation-doped AlAs/GaAs superlattice grown on a semi-insulating GaAs substrate is reported. Their design geometry is reminiscent of the split-drain MAGFET, but their active sensor layer is the two-dimensional electron gas at the AlAs/GaAs heterojunction. A linear response of the relative current imbalance with high sensitivity is obtained below 1-T magnetic induction. Sensitivity is found to be as high as 46%/T for the preferable device geometry with a length-to-width ratio of 2 and split-contact separation-to-width ratio of 0.05, an order of magnitude higher than that of comparable MAGFET designs, The I/O efficiency of signal transformation is very large at small magnetic induction compared to that of conventional magnetoresistors. A simple formula for the sensitivity as a function of Hall mobility and geometry (length, width, and split-contact separation) is derived. >

Device process dependence of low-frequency noise in GaAlAs/GaAs heterostructure

Abstract Low-frequency noise in AlGaAs/GaAs single-heterostructure is studied systematically for various contact metals and device dimensions. The low frequency noise spectra varies at a rate of ƒ −1 in the devices with SnAu contacts, and a rate of ƒ −1.5 in those with AuGe contacts. Contact resistances have no effect on the ƒ −1 noise levels, but change the generation-recombination ( G − R ) noise levels induced by the trap level at 0.23 eV. A large G − R noise bulge by the trap level at 0.8 eV is observed in the AuGe contact devices, but not in those with the SnAu contacts. The noise levels of the SnAu contact device are about 22 dB lower than thoe of the AuGe contact device around 1 Hz.

Very high electron mobility In 0.8 Ga 0.2 As heterostructure grow by molecular beam epitaxy

A very high electron mobility pseudomorphic In0.8Ga0.2As heterostructure is successfully grown on InP both by the elimination of the overshoot of flux densities and by the precise control of the flux ratio through a new calibration technique of RHEED oscillations in an MBE system. The critical layer thickness for the pseudomorphic growth of InGaAs on InP is found to follow the energy balance model, and a very high 2DEG mobility of over 1.5 and 16 m2/Vs at 293 and 10 K, respectively, is obtained.

Critical‐layer thickness of a pseudomorphic In0.8Ga0.2As heterostructure grown on InP

A very high electron mobility pseudomorphic In0.8Ga0.2As heterostructure is successfully grown on InP both by the elimination of the overshoot of flux densities and by the precise control of the flux ratio through a new calibration technique of reflection high‐energy electron diffraction oscillations in a molecular beam epitaxy system. The critical‐layer thickness for the pseudomorphic growth of InGaAs on InP is found to follow the energy balance model, and a very high 2DEG mobility of over 1.5 m2/V s and over 15 m2/V s at 293 and 10 K, respectively, is obtained.

High electron mobility pseudomorphic In0.52Al0.48As/In0.8Ga0.2As heterostructure on InP grown by flux-stabilized MBE

Abstract A very high electron mobility pseudomorphic Si-doped In 0.48 Al 0.52 As/ undoped In 0.8 Ga 0.2 As heterostructure is successfully grown on the InP substrate by the newly invented technology of stabilizing the transient vapor flux of group-III cells with SQRT control and inserting an InAs monolayer in the heterointerface between the channel layer and the spacer. The actual critical thickness of the pseudomorphic heterostructure as determined by the Hall measurement is found to follow the energy balance model, and the highest 2DEG mobilities over 1.6 and 16 m 2 /V·s with 1.6×10 12 cm -2 at 293 and 10 K, respectively, are obtained for the InP-based pseudomorphic In 0.52 Al 0.48 As/In 0.2 Ga 0.2 As heterostructure.

Dependence of Hooge Parameter of Compound Semiconductors on Temperature

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/Vs, realizing 1/f noise in the cross section of optical phonon scattering.

Noise and transport characterisation of tantalum capacitors

Abstract A low frequency noise and charge carrier transport mechanisms were investigated on tantalum capacitors made by various producers. The model of Ta–Ta2O5–MnO2 MIS structure was used to give physical interpretation of I–V characteristics in normal and reverse modes. The noise in time and frequency domain was examined and noise sources were identified. We evaluated correlation between leakage current and noise spectral density and discussed corresponding quality and reliability indicators.