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The influence of temperature and drive current on the Shubnikov-de Haas oscillations is studied as a means to investigate the nature of the electron–phonon interaction in an etched InGaAs quantum wire. The temperature dependence of the energy-relaxation time, and the current dependence of the electron temperature, appear consistent with an energy relaxation process that is dominated by three-dimensional electron–phonon scattering. A deviation from this behavior is found in measurements performed at 1.6 K, however, and simple estimates suggest that this may be associated with the increased importance at low temperatures of phonon confinement in the etched wire.

The critical layer thickness of n-In 0.52 Al 0.48 As/strained-In 0.8 Ga 0.2 As/In 0.52 Al 0.48 As grown on InP substrates was investigated by measuring the photoluminescence spectra. These pseudomorphic heterostructures grown by molecular beam epitaxy attained the highest mobility, 16,200 cm 2 /V·s, at room temperature. The photoluminescence emission intensity decreased in the thickness range of 20 to 25 nm for the In 0.8 Ga 0.2 As layer. These results indicate that the critical layer thickness of this structure follows the energy balance model rather than the mechanical equilibrium model. In addition, this critical value is in good agreement with the results based on the electron mobility behavior.

A trench-type narrow InGaAs quantum-wire field-effect transistor (QWR–FET) with a cross section of 8×25 nm has been fabricated on a (311)A InP V-grooved substrate by molecular-beam epitaxy. The trench-type InGaAs QWR–FET has normal static characteristics at room temperature, and demonstrates clear negative differential resistance characteristics at 40 K with a high peak-to-valley current ratio (PVR=4.3) and a low onset voltage of 0.12 V.

InGaAs quantum wires (QWRs) with cross sections as narrow as 10 nm×20 nm have been fabricated on a (311)A InP V-grooved substrate under an As2 source. Trench-type InGaAs QWRs consist of (111)A and (331)B facets with an angle of about 22°. Cathode-luminescence and photoluminescence measurements confirmed the luminescence peak arising from the QWRs.

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.

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.

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.

Summary form only given. We made a p-i-n photodetector with a superlattice structure. The superlattice consists of 5 quantum wells of GaAs at the thickness of 0.85 nm and 4 barriers of AlAs at the thickness of 0.45 nm in the i-region. The p- and n-region are made of AlGaAs and are transparent for light from a mode-locked Ti:sapphire laser. To avoid the effect of carriers photo-excited in the substrate, we used an AlAs/AlGaAs Bragg reflector. The electric field in the superlattice changes the absorption spectrum, so we can modulate the THz radiation by changing the bias voltage. The electric field in the superlattice is determined by the built-in potential in the p-n junction and changed by the external bias voltage. The superlattice is located 500 nm below the surface, so the surface potential is negligible in the superlattice. The THz radiation from the superlattice was detected by a free-space electro-optic sampling system.

A field effect transistor (FET) using a single InGaAs quasi-quantum wire (QWR) structure as a channel has been fabricated. The quasi-QWR structures have been fabricated with As/sub 2/ flux and atomic hydrogen irradiation using molecular beam epitaxy on V-grooved InP substrate. The V-shape is preserved during InAlAs barrier layer growth due to a suppressed migration of In atoms under As/sub 2/ flux. The V-groove is not preserved and hence the QWR cannot be fabricated under As/sub 4/ flux. The single InGaAs quasi-QWR is used as a channel of the FET. The FET demonstrated the good saturation characteristics and its maximum transconductance is 300 mS/mm at a drain voltage of 0.5 V.

Summary form only given. We have fabricated ultrafast photoconductive switches on a GaAs substrate using an atomic force microscope (AFM) based on anodic oxidation. We report the ultrafast photoconductive switches on a thin absorption layer of low-temperature-grown GaAs which is used to reduce the transit time of carriers.

In this paper, we firstly report the negative differential resistance (NDR) characteristics in ridge-type InGaAs/InAlAs quantum wire field-effect transistor (QWIR-FET) with the /spl delta/-doped layer grown on InP [100] patterned substrate by molecular beam epitaxy. The drain voltage for the onset of NDR and peak-to-valley current ratio (PVCR) are significantly improved by employing QWIR and by decreasing the distance between a source and drain.

A trench-type narrow InGaAs quantum-wire field-effect transistor (QWRFET) on a V-grooved (311)A InP substrate has been successfully fabricated. The trench-type InGaAs QWR-FET with 50 nm gate-length has demonstrated clear negative differential resistance (NDR) characteristics based on real space transfer (RST) with a high peak-to-valley current ratio (PVR=6.2) and a low onset voltage (V/sub NDR/) of 0.1 V. Such a low V/sub NDR/ has not been reported before.

Summary form only. This paper describes the structure and the ultrafast response of insulator-gap photoconductive switches with current block layers.

We have demonstrated a new method to generate intense THz-radiation, up to a sub-microwatt level from a saturable Bragg reflector in a magnetic field. The saturable Bragg reflector is substituted in place of the end mirror in a femtosecond mode-locked Ti:sapphire laser pumped by an all-solid-state green laser.

We have demonstrated a new scheme for generating intense far-infrared or THz radiation pulses synchronously with near-infrared pulses using a saturable Bragg reflector placed inside a mode-locked laser cavity. With this newly proposed simple scheme, THz radiation which peaked at around 0.66 THz, with an average power of 2–3 nW is directly generated synchronously with femtosecond near-infrared optical pulses.

We have constructed a compact, simple high-repetition rate (1 GHz) mode-locked Ti:sapphire laser with self-starting capability using a saturable Bragg reflector as the mode locker. Nearly transform-limited, 1.6-psec pulses were obtained after external dispersion compensation. This laser is potentially pumped by compact green lasers and will be improved to produce a turn-key system.

The effects of low-energy electron irradiation on the two-dimensional electron gases (2DEG's) in AlGaAs/GaAs heterostructures have been investigated. Not only the electron mobility of the 2DEG's but also the two-dimensional (2D) carriers are found to be reduced by the electron irradiation with the incident energies between 3.5 k and 8 keV and the electron dose of 1×1016 and 1×1017 /cm2. The degraded mobility and the removed carriers by the low-energy electron irradiation are shown to recover by isochronal annealing to some extent, but not completely below 400°C. It is also found that considerable amount of scatterers which are created by an electron irradiation at room temperature are also created by an irradiation at 90 K. Comparing the experimental results with the Monte Carlo simulation, we speculate that the mobility degradation and the 2D carrier compensation are partly caused by the formation of complex defects in the GaAs buffer layer which are due to the excitations of core electrons of As, and that the mobility is further degraded by the formation of short-range scatterers in the heterointerface.

Two-dimensional electron gas 60–120-nm deep from the surface was irradiated with 10-keV Ar ions (projected range = 8.8 nm) and resulting change in the mobility was analyzed. Defect distribution thus obtained is exponential in depth with the larger penetration length for the lower irradiation temperature. In-situ Hall measurements revealed that the mobility decreases simultaneously with the irradiation at 90 K. Consequently, the deep penetration of defects is concluded to be mainly due to the ion channeling. Results of iso-chronal annealing indicate that thermal diffusion of the defect that affects the mobility takes place at around 340–400 K, whereas the mobility starts to recover at ∼120 K.

Negative differential resistance with a high peak to valley ratio and low onset voltage is clearly observed in a quantum wire field-effect transistor (QWR-FET) with a channel width of 100 nm, while it is not observed in a QWR-FET with a channel width of 300 nm. The saturation characteristics of Landau plots indicate that the 100 nm wide QWR has one-dimensional characteristics of electron transport, as opposed to the 300 nm wide QWR that has two-dimensional electrons.

InGaAs/InAlAs quantum wire structures on V-grooved InP substrates have been fabricated with As2 flux and atomic hydrogen irradiation using molecular beam epitaxy. Under As2 flux, the V-grooves are preserved during the InAlAs barrier layer growth due to a small migration of the In atoms, but the V-shape is not preserved and hence the quantum wires cannot be fabricated under an As4 flux. The InGaAs quantum wires grown with atomic hydrogen have a narrow photoluminescence peak and a uniform cathode-luminescence image. These phenomena maybe caused by the absence of (311)A sidewall quantum wells due to re-evaporation of the group-III atoms by the atomic hydrogen irradiation.

We have demonstrated a new method to generate intense THz-radiation, up to a sub-microwatt level from a saturable Bragg reflector in a magnetic field. The saturable Bragg reflector is substituted in place of the end mirror in a femtosecond mode-locked Ti:sapphire laser pumped by an all-solid-state green laser.

A field effect transistor (FET) using single InGaAs quasi-quantum-wire (quasi-QWR) as a channel has been fabricated. The quasi-QWR structures were fabricated by selective growth using molecular beam epitaxy on non-planar InP substrate. The width and thickness of the quasi-QWR are 200 nm and 7 nm, respectively. The FET demonstrated good saturation characteristics and its maximum transconductance (gm) was 105 mS/mm at a drain voltage of 0.6 V.

The process of oxidation of titanium using an atomic force microscope was applied for ultrafast metal-semicon- ductor-metal photoconductive switches. The photoconductive gap was formed by oxidation of a 4-nm-thick titanium layer. The photoconductive gap was 43 nm wide and covered with the oxidized titanium. The oxidized titanium is not only a good insulator but also transparent to the excitation beam. A full-width at half maximum(FWHM) response of 770 fs for the transverse component of the electric field was obtained at a bias voltage of 6 V.

The oxidation using an atomic force microscope was applied in the fabrication of ultrafast metal-semiconductor-metal photoconductive switches. The photoconductive gap was formed by the oxidation of a 4 nm-thick-titanium layer. The photoconductive gap which was 100 nm wide and covered with the oxidized titanium which is not only a good insulator but also transparent to the excitation beam. A full width at half-maximum response of 380 fs was obtained at a bias voltage of 10 V.

Hall devices and magnetoresistors totaling a billion per year made of semiconductors are used for displacement sensors of brushless motors in a videotape recorder and disk driver, contactless switches, and bill detectors of vending machine. Conventional magnetic sensors typically have a 100‐μm active region and 1 μm thickness. Two kinds of new magnetic sensors with high sensitivity and high resolution are presented. A semiconductor Hall device made of pseudomorphic InAlAs/InGaAs heterostructures with a high electron mobility of 16 000 and 160 000 cm2/V s, respectively, at 300 and 10 K can be operated in a wide temperature range. A 200‐μm‐square Hall device with a low impedance of 310 Ω and a very thin active layer of 10 nm has a large product sensitivity of 320 V/A T and a maximum magnetic sensitivity of 15 V/T at room temperature. The magnetic sensitivity for current drive increases with decreasing temperature but is constant below liquid‐nitrogen temperature. It is expected that the quantum‐well Hall de...

Evaluating the low-temperature mobility of the two-dimensional electron gas in AlGaAs/GaAs heterostructures, we have studied the nature of the damage induced in the heterostructure by low-energy electron-beam irradiation up to 7.5 keV at room temperature and at 90 K. The isochronal annealing revealed that at around 450 K the degraded mobility recovered quickly in the 90-K-irradiated sample and gradually in the sample irradiated at room temperature. However, the quality of both samples did not recover completely upon annealing at 675 K. The electron-beam irradiation was speculated to cause the formation of As-related defects.

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.

Since the two-dimensinoal electron gas in the modulation-doped A1GaAs/GaAs heterojunction is as thin as 10 nm and the electron mobility is over 7000 cm2/Vs, this structure is suitable for highly sensitive Hall devices. As the room temperature device the following conditions must be satisfied: the carriers should be supplied sufficiently to the two-dimensional gas, but no excess carriers should exist in the highly doped A1GaAs layer. Thus the number of the two-dimensional electron gas should have little dependence on the temperature. The fabrication conditions of the heterojunction and the magnetic property of the devices are discussed. The product sensitivity and the figure of merit of the heterojunction Hall device were 1000 V/AT and 27 (V/A)1/2/T, respectively. These values are comparable to those of InSb Hall devices. The temperature dependence of our device was three times less than that of the InSb Hall device.

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.

Photoluminescence measurements of Be-doped GaAs, grown by molecular beam epitaxy, were carried out at low temperature as a function of acceptor concentration. Results revealed that besides the well-defined emission, [g-g], which is exclusively relevant to acceptor impurities, an additional specific emission, temporarily denoted by [g-g]α is formed near the band-edge, when the concentration of acceptors exceeds 1×1019 cm−3:. From the viewpoint of application it was suggested that also in case of acceptors, photoluminescence spectra can be practically used for the precise determina-tion the acceptor concentration.

Electrical properties of heavily Be-doped GaAs grown by molecular beam epitaxy were investigated systematically in a wide range of Be-concentration from 1× 1014 up to 2× 1020 cm-3 by using yan der Pauw technique. Probable carrier scattering mechanisms observed in this work are discussed by taking into account the radiative mechanisms of several new photoluminescence emissions previously observed in the band-edge-emission region of the samples. All samples were checked their electrical properties first at room-temperature. Five selected samples out of them were measured from 10° K up to room-temperature. Samples having the carrier concentration from 1014 to 1018 cm3 presented typical semiconductor-like conduction with finite carrier excitation energy. For samples having carrier concentration 7× 1016 cm -3, the conduction mechanism at high temperature region above 30β K was dominated by holes thermally excited into valence band. At low temperature region below 30° K . it was dominated by holes hopping from neutral to ionized acceptors with the assistance of phonons. Hole mobilities of samples having the carrier concentration from 1017 to 1018 cm-3 showed an anomalous behavior in the low temperature region, which suggests the presence of a new type of carrier scattering mechanism. A radiative center denoted by lg-gl observed in this concentration region will be a candidate scattering center to explain these electrical behaviors. Samples having the carrier concentration larger than 1019 cm-3 demonstrated typically metallic electric conduction not owing to thermally excited carriers, which means that an impurity band is formed but merged with valence band. The density of state of this combined valence band mixed with impurity band can be supposed to reflect carrier concentration dependence of the PL emission bands observed in this region, i.e. [g-g]α , [g-g]β and [g-g]γ .

We study the quantum-interference characteristics of a 25 nm, trench-type, InGaAs quantum-wire field-effect transistor realized by selective epitaxy, and find very different behavior from that typically exhibited by disordered wires. The amplitude of the magnetoresistance fluctuations is exponentially suppressed at high fields, where evidence of an Aharonov–Bohm effect is observed. The exponential suppression appears to be consistent with theoretical predictions for the influence of magnetic field on the scattering rate in clean wires, while the Aharonov–Bohm effect points to an interference process in which the one-dimensional subbands of the wire themselves constitute well-resolved paths for electron interference.

Ridge-type InGaAs/InAlAs quantum-wire field-effect transistors are realized by selective molecular-beam epitaxy and their transport characteristics are studied. An analysis of the depopulation of one-dimensional subbands in these structures reveals little evidence for sidewall depletion, and yields an estimate for the carrier density in good agreement with that found in two-dimensional InGaAs/InAlAs heterojunctions. Subband splittings as large as 7.4 meV are obtained in the wires, indicating their excellent one-dimensional transport properties.

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.