Masataka Inoue

Characteristics of a Zn0.7Mg0.3O∕ZnO heterostructure field-effect transistor grown on sapphire substrate by molecular-beam epitaxy

Characterization of a Zn0.7Mg0.3O∕ZnO heterostructure field-effect transistor (HFET) is reported. The HFET was based on a Zn0.7Mg0.3O∕ZnO∕Zn0.7Mg0.3O single quantum well (SQW) grown on an a-plane sapphire substrate by molecular-beam epitaxy, and was fabricated by a conventional photolithography technique combined with dry etching. Room-temperature characteristic of the HFET was a n-channel depletion type with a transconductance of 0.70mS∕mm and a field-effect mobility of 140cm2∕Vs, in good agreement with the electron Hall mobility in SQW of 130cm2∕Vs. The on∕off ratio at VDS=3V was ∼800, which was limited by an insufficiently suppressed leakage current through the bottom Zn0.7Mg0.3O barrier.

Surface reaction of III–V compound semiconductors irradiated by As and Sb molecular beams

For the growth of III–VA/III–VB heterostructures with a sharp interface, it is important to suppress the interchanging reaction of column V elements between the impinging molecules (VA) and atoms of the substrates (VB). In order to obtain a systematic understanding, the chemical reaction has been examined for eight different substrate materials with beams of As and Sb. We have determined the critical temperature at which this reaction becomes predominant by using reflection high energy electron diffraction. Raman scattering measurement was also used to analyze the composition of beam-irradiated surface. Experimental results are interpreted reasonably well by the thermochemical property of these III–V compound semiconductors.

ZnO and ZnMgO growth on a-plane sapphire by molecular beam epitaxy

The growth of ZnO and ZnMgO alloy on a-plane sapphire substrates using an Epiquest-MBE system with an RF oxygen plasma cell was studied. Prior to growth, thermal treatment at 680/spl deg/C followed by oxygen plasma irradiation at 500/spl deg/C was performed for the improvement of the surface roughness of sapphire substrates. Then, ZnO layers with thickness of 0.6 /spl mu/m were grown in the range of 400-700/spl deg/C. Two factors were found for obtaining high quality layers. One is the use of a low temperature (250/spl deg/C) ZnO buffer layer and successive thermal treatment at high temperature (750/spl deg/C), which suppressed the formation of twin structure of subsequent layers. The other is the choice of growth temperature. The root mean square (RMS) roughness measured by atomic force microscopy (AFM) was minimized to 0.42 nm when growth temperature was 500/spl deg/C.

Mechanical properties of ZnO epitaxial layers grown on a- and c-axis sapphire

The University of Sydney, for constructive comments and support. The work at UF is partially supported by the AFOSR under Grant Nos. F49620-03-1-0370 sT.S.d and NSF DMR 0400416.

Implant isolation of ZnO

We study ion-irradiation-induced electrical isolation in n-type single-crystal ZnO epilayers. Emphasis is given to improving the thermal stability of isolation and obtaining a better understanding of the isolation mechanism. Results show that an increase in the dose of 2 MeV 16O ions (up to ∼2 orders of magnitude above the threshold isolation dose) and irradiation temperature (up to 350 °C) has a relatively minor effect on the thermal stability of electrical isolation, which is limited to temperatures of ∼300–400 °C. An analysis of the temperature dependence of sheet resistance suggests that effective levels associated with irradiation-produced defects are rather shallow (<50 meV). For the case of implantation with keV Cr, Fe, or Ni ions, the evolution of sheet resistance with annealing temperature is consistent with defect-induced isolation, with a relatively minor effect of Cr, Fe, or Ni impurities on the thermal stability of isolation. Results also reveal a negligible ion-beam flux effect in the case o...

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>>

Influence of Inter-Carrier Scattering on Hot Electron Distribution Function in GaAs

Influences of carrier-carrier scattering on the electron distribution function in GaAs has been examined by the Monte Carlo calculation taking into account electron-electron and/or electron-hole scatterings. The calculated results were compared with the experimental distribution functions determined from the band-to-band recombination spectra under high electric fields.

Molecular‐beam epitaxial growth and interface characteristics of GaAsSb on GaAs substrates

We report the growth by molecular‐beam epitaxy of GaAsSb crystals on GaAs (100) substrates. The composition of the alloyed crystals has been strongly dependent on the growth condition, especially on the substrate temperature and the arrival rates of arsenic and antimony molecules. Raman scattering measurements have been performed to characterize the grown layers, GaAsSb, and GaSb on GaAs substrates. In the GaSb/GaAs grown at relatively high temperatures, we observe the variation of composition near the heterointerface.

Piezoelectric Carrier Confinement by Lattice Mismatch at ZnO/Zn0.6Mg0.4O Heterointerface

This paper describes a strong piezoelectric carrier confinement at a ZnO/Zn0.6Mg0.4O heterointerface grown on an a-plane sapphire substrate by molecular beam epitaxy. A ZnO/Zn0.6Mg0.4O double-heterojunction structure was grown without intentional doping and the formation of a deep potential well for electrons was confirmed using cathodoluminescence and transmittance spectra. Photoluminescence spectra at 4.5 K consisted of an intense near-band-edge emission at 3.359 eV and a broad and weak peak on the low-energy side. The results of Hall effect measurement revealed that the conduction is n-type with a high carrier concentration of ?1.2?1013 cm-2. The mobilities are ?170 cm2/V?s at 300 K and ?400 cm2/V?s at 77 K without deterioration at lower temperatures; these values are much higher than those of a thick single-layer ZnO film grown on an a-plane sapphire substrate. We attribute these optical and electrical properties to the formation of two-dimensional electron gas at the ZnO/Zn0.6Mg0.4O heterointerface by the piezoelectric polarization in a strained ZnO well.

Room-temperature operation of a memory-effect AlGaAs/GaAs heterojunction field-effect transistor with self-assembled InAs nanodots

This letter describes the memory effect of an AlGaAs/GaAs heterojunction field-effect transistor that contains InAs nanodots in the barrier layer. The device experiences a shift of threshold gate voltage, as a function of the amount of the electrons trapped in the nanodots. These trapped electrons can be injected by applying a positive gate voltage and be erased by a visible light illumination at negative gate bias. Although the shift of the threshold gate voltage volatilizes with the time after the memory programing operation, a considerable part of the shift is retained even after 100 h at room temperature.