Yoshiharu Yamauchi

Diamond FET using high-quality polycrystalline diamond with f/sub T/ of 45 GHz and f/sub max/ of 120 GHz

Using high-quality polycrystalline chemical-vapor-deposited diamond films with large grains (/spl sim/100 /spl mu/m), field effect transistors (FETs) with gate lengths of 0.1 /spl mu/m were fabricated. From the RF characteristics, the maximum transition frequency f/sub T/ and the maximum frequency of oscillation f/sub max/ were /spl sim/ 45 and /spl sim/ 120 GHz, respectively. The f/sub T/ and f/sub max/ values are much higher than the highest values for single-crystalline diamond FETs. The dc characteristics of the FET showed a drain-current density I/sub DS/ of 550 mA/mm at gate-source voltage V/sub GS/ of -3.5 V and a maximum transconductance g/sub m/ of 143 mS/mm at drain voltage V/sub DS/ of -8 V. These results indicate that the high-quality polycrystalline diamond film, whose maximum size is 4 in at present, is a most promising substrate for diamond electronic devices.

High-power characteristics of GaN/InGaN double heterojunction bipolar transistors

High-power characteristics have been investigated for GaN/InGaN double heterojunction bipolar transistors (HBTs) on SiC substrates. A base-collector diode showed a high breakdown voltage exceeding 50 V, which is ascribed to a wide band gap of a GaN collector. The maximum collector current is proportional to the emitter size in the emitter-size ranging from 1.5×10−5 to 1.4×10−4 cm2. The corresponding maximum collector current density is as high as 6.7 kA/cm2, indicating the high current density characteristics of bipolar transistors. A 50 μm×30 μm device operated up to a collector–emitter voltage of 50 V and a collector current of 80 mA in its common-emitter current–voltage characteristics at room temperature. The corresponding power density is as high as 270 kW/cm2, showing that nitride HBTs are promising for high-power electronic devices in terms of both the material and the device structure.

In-situ monitoring of GaAs growth process in MOVPE by surface photo-absorption method

Abstract Surface photo-absorption (SPA) is a newly developed in-situ optical monitoring technique for the epitaxial growth process. This method is based on the reflectivity measurement of p-polarized light incident at the Brewster angle. This configuration minimizes the bulk GaAs contribution to the total light reflection. The small change in reflected light intensity between Ga and As atomic surfaces during GaAs growth is thus detected with a high signal-to-noise ratio. By using this characteristic, GaAs growth rate can be monitored in-situ on an atomic scale. In addition to the in-situ monitoring of growth rate, the decomposition processes of Ga and As precursors in MOVPE can be studied by SPA. We demonstrate an investigation of the decomposition process of Ga organometallic, and discuss the growth mechanism of atomic layer epitaxy.

Spectral Observation of As-Stabilized GaAs Surfaces in Metal-Organic Chemical Vapor Deposition Using Surface Photo-Absorption

The spectral dependencies of As-stabilized (001) GaAs surfaces in metal-organic chemical vapor deposition (MOCVD) are measured using the surface photo-absorption (SPA) method and compared them with those obtained in molecular beam epitaxy (MBE). The SPA spectrum of an As-stabilized surface at 600°C is anisotropic in regards to the perpendicularly intersecting incidence azimuths, [110] and [10], of the monitoring light. It is also very similar at a arsine partial pressure of 4 Pa, which is a common MOCVD growth condition, to the spectrum obtained for an MBE As-surface having a c(4×4) reconstruction pattern in reflection high-energy electron diffraction (RHEED) observation, though not to the spectrum corresponding to a(2×4) pattern. Below 500°C, an isotropic signal appears and overlaps with the anisotropic spectrum of a c(4×4)-like surface, indicating that As species adsorbs excessively on a c(4×4)-like surface, which reduces its anisotropy. It is shown that by using different wavelengths, the dynamics of As desorption from each As-stabilized surface can be measured separately.

Flow-rate modulation epitaxy of GaAs and AlGaAs

Flow‐rate modulation epitaxy (FME) is a new epitaxial growth method which can produce a very flat heterointerface and a sharp doping profile. This paper describes FME growth conditions and electrical and optical properties of FME‐grown GaAs, AlGaAs layers, and GaAs/AlGaAs single‐quantum‐well heterostructures. FME can reduce growth temperatures without deteriorating the crystalline quality and can produce flatter heterointerfaces than the metalorganic chemical vapor deposition method. The catalytic decomposition of silane on the Ga atomic surface efficiently dopes silicon into GaAs and AlGaAs with sharp profiles. For p‐type doping, trimethyl metalorganic sources produce carbon atomic layer doping with no memory effect and a low diffusion coefficient of carbon. Experiments using FME to grow modulation doped heterostructures and heterostructure bipolar transistors prove FME to be a promising method of producing III‐V semiconductor devices with thin‐layered structures.

Growth of VPE InP/InGaAs on InP for photodiode application

Abstract Growth procedures and crystal properties of InP grown on InGaAs by vapor phase epitaxy are described. The growth condition for minimizing etch pit density (EPD) is also discussed. Photoluminescence intensity is independent of the examined EPD. Dark current for the diode, however, increases with the EPD. Growth of InP/InGaAs is promising for the fabrication of photodiodes and avalanche photodiodes with high performance in the 1–1.6 μm wavelength regions.

Vapor-Phase Epitaxial Growth of InGaAs on (100) InP Substrate

High quality vapor-phase epitaxial layers were grown on (100) InP substrate with a new and simple apparatus. Crystal properties are discussed. Mobilities were as high as 10050 and 35400 cm/Vs at 300 and 77 K, respectively. These values were comparable to those of epitaxial layers grown by liquid-phase epitaxy. Dark current densities for InGaAs photodiodes fabricated by Zn-diffusion were as low as 5×10-5 and 1.8×10-4 A/cm2 at -5 and -10 V, respectively. These diodes showed breakdown at -79 V.

Structural and Optical Properties of AlGaInN/GaN Grown by MOVPE

Structural and optical properties of AlyGa1-x-yInxN with y from 0.17 to 0.66 and x from 0.01 to 0.08 grown on GaN epitaxial layers by metalorganic vapor phase epitaxy are investigated by X-ray diffraction (XRD), room-temperature photoluminescence (RT-PL), and transmission electron microscopy (TEM). From XRD measurement, it is found that phase separation of AlGaInN occurs with an increase of Al and In contents. For AlyGa1-x-yInxN layers with higher Al (y>50%) and In (x>8%) contents, a long-range ordered structure is observed along the growth direction for the first time by TEM. RT-PL shows single peak band emissions from 300 to 335 nm for the AlyGa1-x-yInxN layers with Al (y>50%) and x from 0.01 to 0.08. By controlling trimethylalminium flow rates and growth temperatures, growth of lattice-matched strain-free Al0.19Ga0.77In0.04N layer to GaN is confirmed by persistent oscillation of in-situ shallow-angle reflectance monitoring and XRD, and 364-nm band emission is observed for the layer in RT-PL.

Gate capacitance-voltage characteristics of submicron-long-gate diamond field-effect transistors with hydrogen surface termination

The radio-frequency characteristics of p-type diamond field-effect transistors with hydrogen surface termination were numerically analyzed using an equivalent-circuit model. From the gate-source capacitance (CGS)-voltage (VGS) results extracted from measured s parameters, the authors found a plateau in CGS within a certain VGS range. This means that a two-dimensional hole gas channel forms parallel to the surface and that the channel is separated by a thin energy-barrier layer with an infinite height from the gate metal. At a high negative VGS, as negative VGS is increased, CGS increases steeply. This results from holes penetrating the energy barrier.

In situ observation of nitridation of GaAs (001) surfaces by infrared reflectance spectroscopy

Abstract Nitridation of GaAs (001) surfaces grown by molecular beam epitaxy is observed by detecting the surface reflectance change caused by the formation of Ga-N and As-N bonds. Nitridation is performed by exposing (4 × 2) or (2 × 4) surfaces to atomic nitrogen generated with a heated tungsten filament in an As-free environment. Nitridation of the Ga-rich (4 × 2) surface results in a single reflectance peak at 1200 cm −1 attributed to the formation of Ga-N bonds, while nitridation of the As-rich (2 × 4) surface results in another peak at 1000 cm −1 attributed to As-N bonds in addition to the Ga-N peak.