Seiji Mukai

Photoluminescent and electrical properties of InGaPAs mixed crystals liquid phase epitaxially grown on (100) GaAs

The liquid phase epitaxial growth of InGaPAs layers on (100) GaAs is described for growth temperatures of 785 and 815 °C. Photoluminescence (PL) spectra and electron Hall mobility of the layers are investigated as a function of crystal composition. The width of PL spectra measured at 300 K is 40 meV, approximately the same value as that of GaAs, when the energy gap Eg of the layers is 1.9 eV or lower than 1.6 eV. The spectral width is around 80 meV when the energy gap of the layers is around 1.75 eV. The increase in the spectral width is attributed to variation of the local energy gap from analysis of dependence of the PL spectra on temperature and on excitation intensity. The indication that local energy gap varies in layers with Eg around 1.75 eV is consistent with the composition dependence of electron mobility. The mobility shows a sharp dip down to 1000 cm2/Vs around this composition, while it depends on composition only slightly for layers with Eg lower than 1.6 eV. The dip in composition dependence...

Doping and electrical properties of Mg in LPE AlxGa1−xAs

Mg‐doped AlxGa1−xAs crystals with Al concentration 0⩽x⩽0.8 have been grown by the conventional LPE method. Doping characteristics of Mg and electrical properties of the crystals are studied using Hall measurements in the temperature range between 77 and 295 K. The results revealed are as follows. Magnesium works as an acceptor in AlxGa1−xAs. Its distribution coefficient is constant and about 0.6 for AlxGa1−xAs with x⩾0.1. Hole concentrations up to 1018 cm−3 are easily obtained for a high x of 0.65. The acceptor energy level Ei increases from 18 meV in GaAs to 40 meV in Al0.8Ga0.2As. The x dependence of Ei can be explained by the difference of effective hole masses and dielectric constants between GaAs and AlAs. Hole concentration, mobility, and resistivity, as well as their temperature dependences, are presented for various x values. These data show that Mg is a suitable acceptor in AlxGa1−xAs particularly with high x values.

Continuous Output Beam Steering in Vertical-Cavity Surface-Emitting Lasers with Two p-Type Electrodes by Controlling Injection Current Profile.

Using vertical-cavity surface-emitting lasers with two p-type electrodes, continuous output beam steering was achieved for the first time by controlling the injection current profile. The far-field peak position can be shifted linearly by varying the ratio between injection currents into the two p-type electrodes. The deflection angle measured from the surface normal direction ranges from -1.3° to +1.0°. Also, we investigated operating characteristics that are important for optical processing such as optical fuzzy inference.

HETEROEPITAXIAL GROWTH OF GaP ON SILICON BY MOLECULAR BEAM EPITAXY.

Heteroepitaxial GaP layers were grown on Si substrates, misoriented by 5° from the (111) face toward the [100] axis, by molecular beam epitaxy (MBE). The RHEED pattern of GaP is of elongated streaks, indicating that the quality of the grown layers is good. From observation by the X-ray divergent beam method, the [111] axis of the grown layers is parallel to that of the substrate. Autodoping of Si into the epitaxial layers from the substrate is very small compared with the layers grown by CVD. Photoluminescence was measured for GaP on Si which was irradiated with an ionized nitrogen beam during MBE.

Optoelectronic fuzzy inference system based on beam-scanning architecture

An approach for implementing a fuzzy inference system by the use of beam-scanning laser diodes is reported. Configurations of the inference system are proposed, and basic experiments of each processing unit are described. The feasibility of the inference technique is also discussed. A PRODUCT-SUM-gravity method of the inference technique is used instead of a conventional min-max-gravity method. Numerical simulation indicates that the PRODUCT-SUM-gravity method leads to higher controllability than the min-max-gravity method. A Gaussian that uses a far-field pattern of a laser diode is an envelope of the membership function. Features of optics, such as scanning the far-field beam and finding the center of gravity of an optical field, are used in the inference processes. Inference speed of the system is faster than several tens of mega-Flips (fuzzy logical inference per second) when one processing unit is used.

Optical tristability using a twin-stripe laser diode

Optical tristability is demonstrated with a positive feedback circuit composed of a twin‐stripe laser diode, a p‐i‐n photodiode, and a transistor. A novel nonlinearity in the current/light characteristics of the twin‐stripe laser diode is the key point in realizing the tristability. By changing the circuit parameters, optical bistability and differential gain characteristics can also be performed.

Laser beam scanning using a local deflector integrated with an effective mode filter

Deflection of a diode laser beam using an injection‐type deflector monolithically integrated with a very long waveguide is demonstrated. The deflector and the waveguide constitute a laser cavity. The waveguide filters out higher order modes, and only the fundamental‐mode light is incident on the deflector. Because the incident light is of a fixed single mode, the deflection of the output beam is very smooth. The deflection mechanism is primarily due to interference between constituent modes for short deflectors, and phase‐front tilting of each mode for long deflectors.

CHARACTERIZATION AND SUBSTRATE-TEMPERATURE DEPENDENCE OF CRYSTALLINE STATE OF GaAs GROWN BY MOLECULAR BEAM EPITAXY.

Thin films of GaAs single crystal were prepared successfully on GaAs (100) substrates by molecular beam epitaxy using an ultrahigh vacuum system with effusion cells and a quadrupole mass analyzer. The dependence of the quality of the GaAs film on the substrate temperature, Ts, was investigated in detail at a constant Ga and As2 arrival rate. The epitaxial process was studied in situ with a high energy electron diffraction (HEED) system. The analysis and characterization of the prepared GaAs films were made with a scanning electron microscope, an ion microprobe analyzer, an ESCA photoelectron spectrometer and photoluminescence measurements. These measurements indicate that GaAs films grown at 480\lesssimTs\lesssim530°C by molecular beam epitaxy have smooth surface and nearly the same quality as bulk crystal.

Liquid phase epitaxial growth of AlGaInPAs lattice matched to GaAs

Liquid phase epitaxial growth of (AlxGa1−x)1−zInzPyAs1−y lattice matched to GaAs is investigated. Uniform layers with high emission efficiency are obtained for x∼0.3 and y<0.1. Distribution coefficients of Al, Ga, In, P, and As at 850 °C are 100, 0.7, 0.03, 100, and 10, respectively. Interpolation formulae of composition dependence of energy gaps and of lattice constant are given and are compared with experimental results.

Transverse second‐order mode oscillations in a twin‐stripe laser with asymmetric injection currents

Transverse second‐order mode oscillations in asymmetrically pumped twin‐stripe lasers are described. Both far‐field patterns and near‐field patterns have two peaks, and a stronger peak appears on the weakly pumped side. The dependence of light intensity in one peak of the far‐field pattern on the current into one stripe shows threshold characteristics. On application of rectangular pulse to one stripe, switching from one peak to the other occurs within 5 ns.