Masahiko Takikawa

Atomic Structure of Ordered InGaP Crystals Grown on (001)GaAs Substrates by Metalorganic Chemical Vapor Deposition

InGaP crystals grown on (001)GaAs substrates by metalorganic chemical vapor deposition are structurally evaluated by transmission electron microscopy. High-resolution electron microscopy observation and electron diffraction analysis of both the (110) and the (10) cross-section specimens strongly suggest that ordering of column III atoms on only two sets of the (111) planes with doubling in periodicity of (111) layers, i.e., In/Ga/In/Ga/In/Ga. . ., is occurring in the crystal. The ordering of the crystal is not perfect, and the ordered regions are assumed to be plate-like microdomains.

Two-Dimensional Electron Gas at GaAs/Ga0.52In0.48P Heterointerface Grown by Chloride Vapor-Phase Epitaxy

We report the first observation of two-dimensional electron gas at GaAs/Ga0.52In0.48P heterointerfaces using the Shub-nikov-de Haas measurements. The heterostructures were prepared by chloride vapor-phase epitaxy. The sheet carrier concentration is higher than that in GaAs/n-AlxGa1-xAs heterostructures with a similar donor-concentration in n-AlxGa1-xAs layers. This may be attributed to the facts that the dominant donors in the Ga0.52In0.48P layers are shallow and that the conduction-band discontinuity at the GaAs/Ga0.52In0.48P interfaces is large.

A 43-Gb/s full-rate-clock 4:1 multiplexer in InP-based HEMT technology

A 43 Gb/s 4:1 multiplexer in 0.13/spl mu/m InP-based HEMT technology contains a 52 Gb/s static D-FF and a phase adjuster giving the D-FF 360/spl deg/ effective phase margin. Microwave techniques and optimization of layout enable 43 Gb/s operation with 43 GHz full-rate clock. Power dissipation is 7.9 W at -5.2 V.

Alloy Fluctuation Effect on Electronic Transition Properties of DX Center Observed with Modified Deep Level Transient Spectroscopy

Alloy fluctuation effects in electronic transition properties of the DX center have been studied in a selectively Si doped Al0.3Ga0.7As/GaAs heterostructure grown by molecular beam epitaxy. Using deep-level-transient-spectroscopy (DLTS) technique, we have measured the drain current transient, from an applied sale pulse for a long gate high-electron-mobility-transistor biased in a linear region. This scheme enables us to record DLTS-like spectra not only for the electron emission process but also for the electron capture process of the DX center. From the analysis of these spectra, we found capture and emission activation energies with Gaussian distributions having wide and narrow band-widths, respectively. This can be explained by considering the large fluctuations of electronic states and the small fluctuations of the spring constant and Jahn-Teller splitting parameter in the DX center cell.

Multi-Wafer Growth of HEMT LSI Quality AlGaAs/GaAs Heterostructures by MOCVD

We report the first successful multi-wafer growth of HEMT LSI quality AlGaAs/GaAs selectively doped heterostructures by atmospheric pressure MOCVD. Highly uniform AlGaAs films with variations in thickness and doping characteristics of less than ± 2.0% and ± 1.5 %, respectively, have been grown on simultaneously revolving and rotating substrates. A trial fabrication of HEMTs resulted in threshold voltage standard deviations as small as 23 mV for E-HEMTs and 35 mV for D-HEMTs distributed over an entire two-inch wafer.

Near-Ohmic Contact of n-GaAs with GaS/GaAs Quasi-Metal-Insulator-Semiconductor Structure

We report on the current-voltage (I–V) characteristics of a metal/ultrathin GaS (thickness<100 A)/n+-GaAs (carrier concentration=2×1018 cm-3) quasi-metal-insulator-semiconductor (QMIS) structure. The GaS was grown by molecular beam epitaxy (MBE) employing the precursor tertiarybutyl-galliumsulfide-cubane ([(t-Bu)GaS]4). The I–V characteristics of the QMIS structure depend on the work function of various metals (Au, Al, Ti). We discovered that a QMIS structure leads to a reduction of Schottky-barrier height itself. Furthermore, we demonstrated near-ohmic contact (contact resistivity=3.7×10-3 Ωcm2) for a Ti/97-A-thick GaS/n+-GaAs QMIS structure. From the relationship between the semiconductor barrier height and the metal work function, we determined that Fermi level pinning was almost eliminated by GaS passivation.

Photo-Excited DLTS: Measurement of Minority Carrier Traps

Novel methods which take into account the temperature dependence of the amplitude of capacitance transient are presented to determine minority carrier trap parameters from Photo-Excited DLTS spectra. These methods were applied to the Fe-level in a GaAs p+n junction and the validity was demonstrated by comparing the results with the conventional junction DLTS.

Invited: Deep Levels in GaAs and GaP

Recent understanding about deep levels in GaAs and GaP is surveyed. Emphasis is placed on some topics of current interest on non-radiative centers, namely, MPE capture theory, junction capacitance techniques, dependence of emission rate and capture probability on temperature. Particular attention is given to the theoretical approach to deep levels in the apparent absence of a review paper on this problem.

Electron and hole traps in N-GaAs crystals

Deep traps were measured and their electronic and optical properties were determined by junction capacitance techniques in n-GaAs crystals grown by different methods. Four electron-traps and four hole-traps were detected. An electron trap was not observed in LPE wafers. A hole trap at 0.45 eV above the top of the valence band was detected in all wafers measured here.

Large-Area MOVPE Growth of AlGaAs/GaAs Heterostructures for HEMT LSIs

We report the large-area metalorganic vapor phase epitaxy growth of AlGaAs/GaAs heterostructures for high-electron-mobility-transistor LSI applications. We used a barrel reactor with a load capacity of twelve 3-inch wafers. Wafer rotation results in ultrauniform epitaxial layers. The variations in both layer thickness and the carrier concentration of a Si-doped AlGaAs layer are less than ±1% over an entire 3-inch wafer. Wafer-to-wafer variations among the twelve wafers are ±1.1% for layer thickness and ±1.8% for the carrier concentration. The particle density on an epitaxial layer is less than 10 cm-2.