Kanji Yoh

An InAs channel heterojunction field-effect transistor with high transconductance

A report is presented on an InAs channel field-effect transistor (FET) based on AlGaSb/InAs/AlSb/AlGaSb structures grown by molecular-beam epitaxy. Excellent pinch-off characteristics have been obtained. An FET with a gate length of 1.7 mu m showed transconductances ranging from 460 mS/mm (at V/sub ds/=0.5 V) to 509 mS/mm (at V/sub ds/=1 V) and a K factor of 1450 mS/Vmm (at V/sub ds/=1 V) at room temperature.<<ETX>>

Electrical characteristics dependence on aluminum mole fraction in (Al0.5Ga0.5)Sb/InAs/(AlxGa1−x)Sb heterostructure

Abstract We have studied the electrical characteristics of the (Al 0.5 Ga 0.5 )Sb/InAs/(Al x Ga 1−x )Sb heterosystems in a variety of samples with different aluminum mole fraction, x . Negative photoconductivity has been observed when the aluminum mole fraction is between 0.2 and 1.0. Reduction of both electron mobility and sheet carrier concentration by the light illumination was post pronounced at x = 0.75. The negative photoconductivity of an (Al 0.5 Ga 0.5 )Sb/InAs/(Al 0.5 Ga 0.5 )Sb structure was found to disappear at high electric fields by pulsed Hall-effect measurements suggesting increased Coulombic scattering being the origin of the negative photoconductivity.

Regular Array Formation of Self-Assembled InAs Dots Grown on Patterned (111)B GaAs Substrate by MBE

We report, for the first time, self-assembled molecular beam epitaxial (MBE) growth of InAs dots on patterned (111)B GaAs substrates by Stranski-Krastanow growth mode. (111)B GaAs substrates were patterned by using conventional optical lithography process and wet-chemical etching. Self-assembled InAs dot growth was performed on both tetrahedral etch-pit pattern and trapezoidal grooves. InAs dots were found to be selectively grown on the bottom of the tetrahedral etch-pit with appropriate growth conditions. As for the growth on trapezoidal grooves, InAs dots were found to be periodically arrayed on the middle of one side of the slope of grooves patterned along [2*BAR*1*BAR**BAR*1*BAR*] direction and on the top and the bottom surface of grooves patterned along [0*BAR*1*BAR*1] direction. The observed periodic distributions of InAs dots on the patterned substrates are presumably caused by the periodic lattice strain distributions on the patterned surface at the initial stage of highly strained layer growth.

Raman scattering analysis of InAs/GaSb ultrathin-layer superlattices grown by molecular beam epitaxy

Abstract Raman scattering analysis has been performed to study characteristic phonon modes in InAs/GaSb ultrathin-layer superlattices (ULSs) grown by molecular beam epitaxy. Either interface bond InSb or GaAs was selectively made in the ULSs by controlling the beam supply sequence during growth. In addition to the acoustic and optic phonons modulated by ULS structure, the Raman spectra were composed of two different types of new phonon mode localized at each interface of InSb or GaAs. These experimental data have been understood in agreement with the theoretical analysis.

A Novel Bistable Double-Barrier Resonant Tunnel Diode by Charging Effect of InAs Dots

We report on a novel bistable current voltage characteristics of GaAs/AlGaAs double-barrier resonant tunnel diodes (DBRTDs) with self-assembled InAs dots buried in the GaAs cathode layer. The memory effect was observed at room temperature and is likely to be caused by the charging and discharging of InAs dots, where the discharging takes place through tunneling via resonance states in the adjacent quantum well.

Structural stability of ultrathin InAs/GaAs quantum wells grown by migration enhanced epitaxy

Abstract In order to study the strained-structure of InAs films on GaAs substrates, photoluminescence (PL) properties have been examined for ultrathin InAs/GaAs single quantum well (SQW) structures grown by migration enhanced epitaxy. Observed PL spectra from SQWs are discussed in conjunction with in-situ monitored growth conditions of the heterostructure by using reflection high energy electron diffraction. Rapid thermal annealing on the grown samples has been performed to understand the stability of strained heterostructure. By the PL analysis on the annealing effect, the critical thickness for the stably strained heterostructure is determined to be 2–3 MLs and nearly 1 ML for samples grown at 520 and 420°C, respectively.

Quantized conductance observed at high temperatures in InAs/(AlGa)Sb quantum wires

We report the first demonstration of the 1D quantized conductance at around 80 K on InAs/(AlGa)Sb split gate devices fabricated by using electron beam lithography and wet chemical etching. Nonlinear transport properties measured between 4.2 K and 115 K are discussed.

Electron and thermal transport in InAs single-crystal free-standing wires

We report electron and thermal transport in InAs nanostructure free-standing wires fabricated by electron beam lithography and wet-chemical etching on an InAs/AlGaSb heterostructure grown by molecular beam epitaxy. Conductance measurements of InAs free-standing wires with the thickness of 150-550 AA and a few thousand angstroms wide were conducted by non-dissipative AC measurement over the temperature range between 4.2 and 40 K. The dependence of resistance on heating current revealed that the Wiedemann-Franz law holds when the power dissipation is below approximately=3 nJ. Above the critical power dissipation, the I-V characteristics show deviation from the simulation curve which takes into account the electric contribution, the phonon drag thermopower, the diffusive thermopower, the electron-phonon generation term, blackbody radiation, and thermal diffusion from the surface to the helium atmosphere of the cryostat. The experimental results suggest some other heat conduction mechanism which does not contribute to the electric conduction.

Fabrication of Superconducting Transistors using InAs/(AlGa)Sb Quantum Wells

We report on a fabrication process of superconducting weak links and superconducting transistors, which contain two-dimensional electrons in InAs/(AlGa)Sb quantum well. The superconducting transistors with lead alloy superconducting contacts were fabricated by using electron beam lithography, lift-off, and wet chemical etching processes. We have succeeded in fabricating a superconducting transistor with 0.4 µ m channel length and 0.17 µ m gate length between superconducting electrodes. Although the ideal performance of superconducting transistors has not been achieved yet, we present the results of superconducting weak links. The process of reducing contact resistance between lead alloy and InAs is also discussed, which is crucial to demonstrate the performance of the superconducting transistor.

One-dimensional electron transport in InAs/(AlxGa1-x)Sb SQWs

The authors report 4.2 K magnetoresistance measurements of InAs quantum wires based on AlGaSb/InAs/AlGaSb heterostructures grown by molecular beam epitaxy (MBE). The widths of the channel have been defined by electron-beam lithography and wet chemical etching. In the low magnetic field region, the Landau plots deviated from the linear relations indicating the lateral confinement. In the high magnetic field region, pronounced spin-splitting of Landau levels was observed in quantum wires compared with two-dimensional electron gas.