Mutsuyuki Otsubo

A 1.9-GHz-band GaAs direct-quadrature modulator IC with a phase shifter

A 1.9-GHz-band direct-quadrature modulator IC has been developed for digital cordless telephone use. In the 1.9-GHz high-frequency band, both carrier and image rejections as low as -40 dBc have been obtained with low-power dissipation of 110 mW, corresponding to phase error below 1.1 degrees . A newly developed circuit configuration, which combines a quadrature phase shifter with drivers, make this excellent spectrum efficiency and low-power dissipation possible. This modulator IC is expected to contribute to the realization of enhanced digital mobile communication systems such as digital and cordless digital cellular telephones.<<ETX>>

A single-chip GaAs RF transceiver for 1.9-GHz digital mobile communication systems

A 1.9-GHz single-chip GaAs RF transceiver has been successfully developed using a planar self-aligned gate FET suitable for low-cost and high-volume production. This IC includes a negative voltage generator for 3-V single voltage operation and a control logic circuit to control transmit and receive functions, together with RF front-end analog circuits-a power amplifier, an SPDT switch, two attenuators for transmit and receive modes, and a low-noise amplifier. The IC can deliver 22-dBm output power at 30% efficiency with 3-V single power supply, The new negative voltage generator operates with charge time of less than 200 ns, producing a low level of spurious outputs below -70 dBc through the power amplifier. The generator also suppresses gate-bias voltage deviations to within 0.05 V even when gate current of -144 /spl mu/A flows. The IC incorporates a new interface circuit between the logic circuit and the switch which enables it to handle power outputs over 24 dBm with only an operating voltage of 3 V. This transceiver will be expected to enable size reductions in telephones for 1.9-GHz digital mobile communication systems.

0.78- and 0.98-/spl mu/m ridge-waveguide lasers buried with AlGaAs confinement layer selectively grown by chloride-assisted MOCVD

The 0.78- and 0.98-/spl mu/m buried-ridge AlGaAs laser diodes (LDs) with a high Al-content AlGaAs confinement layer selectively grown by using a Cl-assisted MOCVD are demonstrated. By employing the AlGaAs confinement layer, the threshold current and the slope efficiency of the 0.78-/spl mu/m LD are improved by /spl sim/40%, compared to those of the conventional loss-guided LD with the GaAs confinement layer. In addition, the stable fundamental mode up to 150 mW and the small astigmatic distance less than 1 /spl mu/m are obtained. The 0.78-/spl mu/m LD also shows the excellent high-power and high-temperature characteristic such as 100 mW CW operation at 100/spl deg/C and the reliable 2,000-hour operation under the condition of 60/spl deg/C and 55 mW. In the 0.98-/spl mu/m LD, the narrow beam with the low aspect ratio of 1.86 and the stable fundamental transverse mode over 200 mW are exhibited. As a result, the 0.98-/spl mu/m LD realizes the high fiber-coupled-power of 148 mW. Moreover, the high-power and high-temperature operation of 150 mW at 90/spl deg/C is obtained. In the preliminary aging test, the LDs have been stably operating for over 900 hours under the condition of 50/spl deg/C and 100 mW. >

Radiation Annealing of Si- and S-Implanted GaAs

Radiation annealing of Si- and S-implanted GaAs using tungsten lamps was studied. In capless radiation annealing, electrical activations were 70–80%, which were 20–30% higher than that in conventional furnace annealing for a low dose below 2×1013 cm-2. Effects of encapsulation on electrical activation were also investigated. It was found that electrical activations of high dose samples were improved by encapsulating the surface with SiO2 film for Si-implanted samples and with Si3N4 film for S-implanted samples.

High quality Si-doped GaAs layers grown by molecular beam epitaxy

Abstract High quality Si-doped MBE. GaAs layers with high reproducibility have been grown by minimizing the incorporation of impurity species. The electrical and optical properties, and the doping characteristics of the Si-doped layers have been studied, and compared with those of Sn-doped layers. Hall mobility has indicated a low level of compensation in both the Si- and Sn-doped layers. The photoluminescence intensity of the Si-doped layers has been as high as that of the Sn-doped layers. Si-doped layers have shown more abrupt doping profiles than those of the Sn-doped layers, even when the surface segregation effect of the Sn-doped layers has not been observed. The difference in the doping profiles between the Si- and Sn-doped layers is discussed.

Photoluminescence Study of Defects in GaAs Formed by Annealing in an H2 Gas Flow

GaAs crystals were annealed in an H2 gas flow and the degraded layer formed on the surface by annealing has been investigated by a photoluminescence measurement. The origin of the defects, in particular an emission at 890 nm, formed by annealing has also been investigated with the aid of the liquid phase epitaxy technique. The degradation of the surface is governed by self-diffusion of As vacancies. The degraded layer depth increases in proportion to the square root of the heating time, whose rate depends on carrier concentrations in the crystals. As the crystals are annealed in an H2 gas flow, new emission band at 890 nm grows drastically. It is concluded that the band is due to electron transitions from a shallow donor to an As vacancy acceptor.

Chemical beam epitaxial growth of Si‐doped GaAs and InP by using silicon tetraiodide

Silicon tetraiodide (SiI4), which has a very weak Si–I bond strength (70 kcal/mol), is successfully employed as a novel Si dopant in the chemical beam epitaxy of GaAs and InP. No precracking is necessary before supplying SiI4 with He carrier gas. High electrical quality is ascertained for both GaAs and InP with linear Si doping controllability in the range from 2×1016 to 6×1018 cm−3 with a uniformity of less than 2% within a 3‐in.‐diam area. The electron mobility in a GaAs with a carrier concentration of 1×1017 cm−3 is 4400 cm2/V s and that in InP with a carrier concentration of 4×1017 cm−3 is 2400 cm2/V s, respectively. Abrupt interfaces and precise on‐off controllability without any memory effect is also confirmed by secondary‐ion‐mass, spectroscopy measurements. The electrical activation ratio of Si in SiI4 for both GaAs and InP is almost 100% in the range studied here. These versatile features suggest that SiI4 is a promising candidate as a Si dopant source for chemical beam epitaxy growth.

The Ga–In–Sb Ternary Phase Diagram at Low Growth Temperature

The ternary phase diagram of the Ga–In–Sb system was investigated. The solidus isotherm at 400°C and liquidus isotherms at 400, 500, and 600°C were determined experimentally. The phase diagram of Ga–In–Sb system was calculated on the basis of various thermodynamic parameters. It is found that the calculation with the modified Delta Lattice Parameter (DLP) model best fits the experimental solidus isotherm at 400°C.

Study on the accumulated impurities at the epilayer/substrate interface and their influence on the leakage current of metal-semiconductor-field effect transistors

Carrier impurities accumulated at the interface of a molecular beam epitaxial (MBE) grown GaAs layer-substrate have been studied in connection with substrate surface preparation just prior to MBE growth. Although the accumulated impurity density of silicon (higher than 7 × 1017 cm-3) at the interface is the same for both H2SO4- and HF-treated samples, the oxygen level is much higher for the H2SO4-treated (higher than 1 × 1019 cm-3) than for the HF-treated sample (less than 2 × 1018 cm-1). High density of carriers (higher than 7 × 1017 cm-3 is found to be accumulated at the interface only for the HF-treated sample. Further, absorbances at 1080 and 1260 cm-1 in FTIR spectra, which correspond to Si-O bonds, are observed only for the H2SO4-treated sample. The accumulated carrier concentration obtained in the HF-treated sample is thought to originate from the accumulated silicon which is not inactivated by making Si-O bonds. The accumulated impurities depend upon the initial surface condition of GaAs substrate before growth. The arsenic passivation layer has a good effect on reducing the accumulated impurities, which causes the carrier accumulation.

GaxIn1-xSb Crystals Grown by Liquid Phase Epitaxy

Epitaxial layers of GaxIn1-xSb have been gown on GaSb and/or InSb substrates over the whole composition range. The influences of the growth conditions on the crystalline qualities of GaxIn1-xSb have been investigated by an optical microscope and the X-ray Kossel patterns. Single crystalline layers can be gown in the composition range, 0≤x≤0.93 on (111) InSb substrates and in the range, 0.70≤x≤1 on (100) GaSb substrates. The etch pit density in the grown layer was about 107 cm-2, independent on the substrates and composition x. A considerable increase in the etch pit density in the substrate was observed after epitaxial growth. Ga was detected in the InSb substrate after epitaxial growth.