Toshinobu Matsuno

High-quality InxGa1-xAs/InAlAs modulation-doped heterostructures grown lattice-mismatched on GaAs substrates

Abstract We report on the lattice-mismatched growth and properties of InGaAs/InAlAs modulation-doped heterostructures on GaAs substrates for a full In composition range, by molecular beam epitaxy using a linearly graded InGaAs or InGaAlAs buffer layer grown at a relatively low temperature. High electron mobilities of 25,000 to 118,000 cm2/V⋯s were obtained at 77 K for In composition from 0.3 to 0.8. The observed monotonical increase of mobility in this In composition range agreed well with the theoretical calculation. It has been shown that the use of wider bandgap material, such as InGaAlAs, in the graded buffer layer is very effective in reducing the residual carrier concentration from 1×1012 to less than 1x1011 cm−2.

A high-power RF switch IC using AlGaN/GaN HFETs with single-stage configuration

A high-power single-pole double throw (SPDT) switch IC using AlGaN/GaN heterojunction field-effect transistors (HFETs) is demonstrated for the first time. The reduction of on-resistance (R/sub on/) and off-capacitance (C/sub off/) for AlGaN/GaN HFETs enables the GaN-based switch IC that can be applied for practical RF applications. A novel Si-doping technique is employed to reduce ohmic contact resistance, which successfully reduces the R/sub on/. The C/sub off/ of the HFETs on a sapphire substrate is found to be smaller than that on a SiC substrate, together with low cost fabrication. The GaN-based SPDT switch IC with single-stage configuration is designed by using a circuit simulator based on the extracted device parameters. The fabricated SPDT switch IC achieves insertion loss of 0.26 dB and isolation of 27 dB at 1 GHz, as well as an extremely high-power handling capability of 43 W. This value is 10 times higher than that of typical GaAs-based switch ICs. In addition, the switch IC exhibits low distortion characteristics, where the third-order intercept point of 41 dBm is achieved. The chip size is reduced to 40% as compared with conventional four stage GaAs-based switch ICs by using the single-stage circuit configuration.

Lattice-Mismatched Growth and Transport Properties of InAlAs/InGaAs Heterostructures on GaAs Substrates

We report on the lattice-mismatched growth of In0.53Ga0.47As/In0.52Al0.48As modulation-doped heterostructures on GaAs substrates by molecular beam epitaxy. A buffer layer structure and its growth conditions were optimized. As a result, we obtained a sample with a mirrorlike surface which exhibits electron mobility of 10500 cm2/Vs and 48500 cm2/Vs at 300 K and 77 K, respectively. These values are comparable to those obtained in lattice-matched structures grown on InP substrates. To our knowledge, the room temperature mobility is the highest ever reported in a modulation-doped heterostructure grown on a GaAs substrate.

In0.5Ga0.5As/InAlAs Modulation-doped Field Effect Transistors on GaAs Substrates Grown by Low-Temperature Molecular Beam Epitaxy

We report on the lattice-mismatched growth and electrical properties of In0.5Ga0.5As/InAlAs modulation-doped heterostructures on GaAs substrates by molecular beam epitaxy using a wide-gap InAlAs graded buffer layer and low-temperature Molecular Beam Epitaxial growth at about 350°C. A drastic reduction in residual carrier accumulation has been achieved, and a high electron mobility at room temperature of 11100 cm2/Vs was obtained with an electron concentration of 3×1012/cm2. It was found that the cause of residual carrier accumulation is related to the growth interruption or temperature rise after the growth of the graded buffer layer. The fabricated Modulation-doped Field Effect Transistors showed low output conductance, good pinch-off characteristics and no kink effect. The higher transconductance of 270 mS/mm was also obtained.

A MOS Image Sensor With a Digital-Microlens

We have developed a MOS image sensor with digital-microlenses (DMLs), each of which has an effective refractive index realized by variation of the subwavelength separations between the concentric SiO2 ring walls. The effective refractive index profiles are optimized for the location of each pixel. The light-collection efficiency of the image sensor is twice as high as that of a conventional image sensor because of the enhanced light acceptance in the periphery. A 2.2-mum pitch 3-megapixel MOS image sensor based on the DML technology exhibited excellent uniformity of the light-collection efficiency across the image area, even for light with a very large incident angle, i.e., over 45deg. The DML promises new levels of performance of image sensors.

Photoluminescence of an InAlAs/InGaAs Quantum Well Structure Grown on a GaAs Substrate

An In0.53Ga0.47As/In0.52Al0.48As quantum well structure was grown on a GaAs substrate by molecular beam epitaxy. A linearly graded InGaAlAs layer grown at 380°C was used as a buffer layer. The photoluminescence of this structure was observed at 15 K. The InGaAs quantum well thicknesses ranged from 20 A to 500 A. Emission of each quantum well was clearly resolved. The luminescence linewidths were analyzed and compared to the results reported for the material system grown lattice-matched to InP. We deduced an enhancement of the alloy clustering and well thickness fluctuations which probably do not exceed 1 monolayer but which have a large lateral extension. These features are related to the lattice mismatch of the structure with the substrate.

A millimeter-wave flip-chip IC using micro-bump bonding technology

This millimeter-wave flip-chip IC (MFIC) is a compact hybrid constructed by bonding a mm-wave transistor or its IC chips upside down on thin film microstrip lines formed on a Si substrate. Production costs of this IC are expected to be drastically reduced compared with those of the conventional MMIC because the passive elements, which usually occupy large chip area, are formed not on the expensive heterostructure substrate, but on the low-cost Si substrate. Moreover, design flexibility such as a device choice and integration is expanded including the integration of antennas. Using 9 /spl mu/m-thick p-CVD SiO/sub 2/ as a dielectric film, microstrip lines on Si substrate were realized. Using MBB technology to fabricate K-band MFIC amplifiers demonstrates the MFIC concept.

InyGa1−yAs/InyAl1−yAs resonant tunneling diodes on GaAs

Resonant tunneling diodes are fabricated using InyGa1−yAs/InyAl1−yAs on GaAs substrates for the first time. The devices showed increasing peak current density as the In content was raised from 0 to 0.3, which is shown to be consistent with the Γ valley being the predominant transport mechanism at the tunneling resonance. Devices with y=0.2 showed an average peak to valley current ratio of 4.2 at room temperature, versus 3.3 for y=0. The decrease in the peak to valley current ratio is attributed to a decreased tunneling component in the X valleys of the In0.2Al0.8As barrier layers. Devices with y=0.3 show room‐temperature peak to valley current ratios of approximately 2.5; the increased valley current is attributed to interface roughness scattering and other effects.

THE IMPACT OF USING ALGAAS AS A CARRIER SUPPLYING LAYER IN AN INALAS/INGAAS HIGH ELECTRON MOBILITY TRANSISTOR STRUCTURE ON THERMAL STABILITY

The impact of using a thin AlGaAs layer as a carrier supplying layer in an InAlAs/InGaAs high electron mobility transistor structure (HEMT) on thermal stability has been investigated. The new structure exhibited no deterioration in its sheet carrier concentration after annealing for 15 min at 450 °C in nitrogen atmosphere, while in the conventional HEMT structure 20% deterioration was observed. The secondary ion mass spectroscopy analysis indicated that this excellent thermal stability originated from the absence of reaction between dopant and fluorine. By exposing the new and conventional HEMT structure in a fluorine atmosphere, it was obvious that the new structure had at least a five times higher tolerance to fluorine.

Low-noise InGaAs HEMT using the new off-set recess gate process

A low-noise InGaAs HEMT (High electron mobility transistor) with a noise figure of 0.68 dB at 12 GHz has been developed using the offset recess gate process. The pseudomorphic n-AlGaAs/InGaAs HEMT structure was grown on a semi-insulating GaAs substrate by molecular-beam epitaxy. The offset recess gate process makes it possible to decrease the source and gate resistance. The breakdown voltage between gate and drain were above 6 V. A G/sub m/ of 510 mS/mm at minimum noise bias point was obtained in a 0.2- mu m-gate InGaAs HEMT. The minimum noise figure and associated gain of the device are 0.68 dB and 10.4 dB at V/sub ds/=2V, I/sub ds/=16 mA, and f=12 GHz, respectively. A three-stage amplifier using the new HEMT at the head has shown a minimum noise figure of 1.2 dB and a maximum gain of 31 dB.<<ETX>>