Ichiro Shibasaki

Transport properties of Sn-doped InSb thin films and applications to Hall element

Abstract The temperature dependence of the transport properties of undoped and Sn-doped InSb single crystal thin films grown on GaAs substrates by MBE were investigated. The temperature dependence of undoped InSb thin films was large and had maximum near room temperature, whereas the Sn-doped thin films showed very small and monotonic decrease with increasing temperature. The electron mobility of the films varied significantly in the growth direction from the InSb/GaAs hetero-interface to the InSb thin film surface. This large variation of the electron mobility in the growth direction explained the observed temperature dependence of the electron mobility for these films. The large variation of the electron mobility in the growth direction was described by a simple model of two layers with a low electron mobility layer near the hetero-interface and the other with a high electron mobility. These InSb films were used to fabricate practical and highly sensitive Hall sensors with a very small temperature dependence.

High sensitivity Hall elements made from Si-doped InAs on GaAs substrates by molecular beam epitaxy

Abstract We have newly developed Hall elements consisting of Si-doped InAs thin film grown on GaAs substrate by molecular beam epitaxy (MBE). By doping Si into the layer of InAs thin films far from the InAs/GaAs interface, InAs thin films with high electron mobility are obtained and temperature dependent variations of the electron mobility and sheet resistance are much reduced. These InAs thin films were processed into Hall elements with practically useful characteristics.

Properties and applications of Sn-doped single crystal thin film magneto-resistance elements

Using Sn-doped single crystal InSb thin films of 1.0-/spl mu/m thickness grown on GaAs substrates by molecular beam epitaxy, new magneto-resistance elements with very small temperature dependence were developed. Using these magneto-resistance elements, the contactless detection of the rotation speed of rotating gear teeth over a wide range of rotation speeds was studied. The output voltage from the magneto-resistance element was independent of the rotation speed of the gear, and exhibited good temperature stability and very small sine wave sine wave distortion, which allowed fine detection of the angular velocity of the rotations.

Properties of InAs thin films grown on (100)-oriented GaAs substrate with various tilted angles and directions of misorientation

Abstract We studied the dependence of the surface morphology and the sheet carrier density of InAs thin films epitaxially grown on (100)-oriented GaAs substrate with various misorientations of tilt directions and angles of tilt. We also studied the relation between the directions of tilt and the device properties of Hall elements fabricated from InAs thin films grown on GaAs substrates. With a misorientation of 2°, we found a strong dependence of the offset voltage on the direction of tilt of the GaAs substrate. We applied these results to the fabrication of practical InAs Hall elements by molecular beam epitaxy. These Hall elements are now commercially available as magnetic sensors. Over five million Hall elements have been applied to current sensors and brushless motors in electronic appliances.

Interfacial trap states and improvement of low-temperature mobility by doping in InSb/AlInSb quantum wells

The effect of doping on InSb/Al0.1In0.9Sb quantum wells (QWs) was investigated, and it was found that doping improves the electron mobility at low temperatures and leads to a weaker dependence of the resistivity with temperature. The dependence of the carrier density on the well width revealed trap states at the interfaces of the QW whose sheet density per interface was estimated to be about 4 × 1010 cm−2. The low mobility of undoped InSb QWs, in particular, at low temperature seems to have been caused by positively ionized impurity scattering at the interfacial trap states. Doping compensates for the trap states and enhances mobility by suppressing ionized impurity scattering. Thus, intentional doping is necessary for developing high-mobility InSb QW devices. The origin of the trap states is qualitatively discussed.

Magnetoresistance effect of InAs quantum well structure grown on GaAs substrates by molecular beam epitaxy

We have developed a new type of semiconductor magnetoresistance sensor. InAs deep quantum well structures (InAs DQWs) were grown on a GaAs substrate with AlGaAsSb insulating layers by molecular beam epitaxy (MBE). The magnetoresistance effect of these InAs DQWs has been measured for the first time. The large magnetoresistance and geometrical effect of a InAs DQWs MR element have been observed. The InAs DQWs MR sensor is promising for future magnetic sensor applications, such as those in automobiles.

Negative and Positive Magnetoresistance in Variable-Range Hopping Regime of Undoped AlxIn1−xSb/InSb Quantum Wells

Low-temperature magnetoresistance (MR) in the variable-range hopping (VRH) regime of undoped AlxIn1−xSb/InSb quantum wells was studied. The low-T resistance shows that the two dimensional (2D) Mott VRH crossovers to Efros-Shklovskii (ES) VRH due to the Coulomb interaction with lowering T. The anisotropic negative MR in weak magnetic fields was explained by the quantum interference in the VRH. The in-plane positive MR in higher fields found in ES VRH regime was attributed to the spin-Zeeman effect that suppresses the hops between singly occupied states in the presence of intra-state correlation. As for the orbital MR subtracted from perpendicular MR, in deeply insulating regime the negative MR saturates above a characteristic field followed by an exponential increase of the positive MR in agreement with the quantum interference and the subsequent shrinkage of wave functions with increasing field, while in barely insulating regime of the 2D metal-insulator (MI) transition a large negative MR inexplicable survives even in the extremely high magnetic-fields.

Application of Sn-doped InSb Single Crystal Thin Film Magneto-resistance Devices to Detecting Gear-rotation Speed

We could accurately detect the rotation angle or speed of the spindle axis of the motors used for industrial purposes by using a combination of an iron gear and a magnetic sensor device with a bias permanent magnet. The relation between the accuracy of detecting the rotation angle and the deviation from the sine curve of the output signal from the magnetic sensors was studied by analyzing the magnetic field. A device made from a bridged pair of magneto-resistance (MR) elements demonstrated the smallest deviation and the best accuracy of three kinds of magnetic sensors, such as a bridged pair of MR-elements, a bridged pair of MR-single element and a fixed resistor, and a Hall element (HE) used as a magnetic sensor. The results were also verified from experiments.

Quantum Hall Effect and Spin Resolved Anti‐crossing of Landau Levels in AlGaSbAs/InAs and AlInSb/InAsSb Quantum Wells

We have investigated transport properties in InAs/AlGaSbAs and InAsSb/AlInSb quantum wells (QW) in the quantum Hall regime. The carrier density in InAs QW is tuned by using a front gate bias, and the contour plot of resistance as a function of perpendicular magnetic field and gate voltage reveals the spin‐resolved subband‐Landau‐level coupling in tilted magnetic fields. An anomalous transport occurred by the coexistence of electrons and holes in the system has been observed both in InAs and InAsSb QWs.

SPIN RESOLVED SUBBAND-LANDAU-LEVEL COUPLING AND ELECTRON-HOLE COUPLING IN InAs/AlGaSbAs QUANTUM WELL

We have investigated the magneto-transport properties in InAs/AlGaSbAs quantum well (QW), where the lattice mismatch is less than 0.5%. In tilted magnetic fields, the spin-resolved subband-Landau-level coupling has been clearly observed in the magneto-resistance due to the large g-factor of this QW. An anomaly in the Hall effect has been observed at high magnetic fields of the filling factor being less than unity, which is caused by the coexistence of electrons and holes in the system.