ALBERT

Notes: Magnetic bar codes can be used in unclean environments, where widely used optical bar code systems cannot be applied. Readout system for magnetic bar codes can also be made much simpler than optical ones. A new magnetic bar code system is proposed, in which binary information is coded in the sign of tilted angles of magnetic strips from a given standard direction. This scheme is unique compared to the conventional optical bar code, where width or space of the parallel pattern carries information, or an already reported magnetic bar code, where cross sectional shapes of pattern engraved in a ferromagnetic body carries information. Each of the magnetic strips brings about magnetic anisotropy due to its shape effect, hence angular dependent permeability in the proximity of the strip. The sign of the tilted angle of each magnetic strip is detected inductively through the angular dependent permeability by using a magnetic pickup head with a pair of cross-coupled figure-eight coils, where the sign of mutual inductance between the primary and the secondary figure-eight coil has one to one relationship to the sign of the tilted angle.Because the detection of the tilted angle is independent of scanning speed, variation in the scanning speed of the readout head does not affect the performance. In our preliminary study, the proposed magnetic bar code system was examined using pickup head consisting of a pair of cross-coupled 10-turn figure-eight coils which was embedded in a rectangular ferrite rod with cross-shape groove on the top surface of 6.5×3 mm dimension. The head was made thinner in the scanning direction to allow dense alignment of the pattern. Two kinds of pattern were made: the one was by aligning short amorphous wires (5 mm in length and 120 μm in diameter) on the plastic film and the other by using a thin (10 μm in thickness) copper film with tilted slits backed by an amorphous ribbon. These samples of magnetic bar code patterns were scanned with lift-off of 1 mm under the operating condition of 120 kHz and 200 mA. Amplitudes of the positive and the negative peak of the output voltage well exceeded 10 mV. Density of the pattern in the preliminary study was 7 bits for the bar code length of 2.6 cm. We will discuss several factors to make density of the pattern higher. Because the pickup coils can be assembled with planar coils and because the magnetic bar code itself is thin, the total system of this bar code scheme can be realized in thin form. © 1996 American Institute of Physics.

Notes: Origin of a nonradiative center in AlGaAs grown by molecular-beam epitaxy was investigated by secondary ion mass spectroscopy and deep-level transient spectroscopy, from the change of photoluminescence intensity with anneal treatment, and from its comparison with GaAs. Aluminum-oxygen complex is a most probable defect which acts as a nonradiative center in AlGaAs, and the oxygen would evaporate as Al2O from the surface, which would be a reason why the photoluminescence intensity increases under higher substrate temperature and lower V/III flux ratio. The electron-trap level at 0.76 eV from the conduction band would be the recombination center, and the photoluminescence intensity is inversely proportional to the trap concentration.

Notes: GaAs/AlGaAs heterostructure selectively doped with Si was grown in a conventional normal pressure metalorganic chemical vapor deposition using trimethyl metals and arsine. Mobility of the two-dimensional electron gas as high as 8100, 148 000, and 401 000 cm2/V s was obtained at 300, 77, and 5 K, respectively, for a sample with an undoped Al0.3Ga0.7As spacer layer of 100 A(ring) and with a sheet electron density of about 5×1011 cm−2. The heterostructure with the spacer layer thinner than 100 A(ring) shows high mobility comparable to the best values obtained by molecular-beam epitaxy. The influence of growth parameters on the electron mobility in the heterostructure is described in detail.

Notes: Optical properties were investigated on the superlattices with a unit lattice period of (AlAs)n(GaAs)n (n=1–24) which were grown by atmospheric-pressure metalorganic chemical vapor deposition. Raman spectroscopy indicated that superlattice structure is realized for each n without collapsing into alloys. Photoluminescence measurement indicated that the ultrathin-layer superlattice (with n larger than 2) has a direct energy gap, which is in good agreement with a tight-binding calculation.

Notes: A Weissenberg camera for macromolecules with imaging plate data collection system at BL6A and BL18B stations in the Photon Factory is introduced and evaluated. The special feature of these systems is considered matching for both SR-x rays and protein crystallography. This system is user-friendly and can collect a large amount of data to higher resolution from the crystal with large unit cell dimensions. A newly developed camera can be used as a time-resolved Laue camera and a Weissenberg camera. A large image reader (IPR4080) that can scan 400×400 mm2 and 400×800 mm2 sizes of imaging plates has been developed and evaluated. The new data collection system combined with the new camera and IPR4080 will be installed at the BL18B station in October 1994. © 1995 American Institute of Physics.

Notes: Phase-locked array lasers with large optical waveguide structures are demonstrated. The refractive index guides of each laser are evanescently coupled with and without offset-coupling structure. An evanescently coupled three-element laser array without offset coupling regions emits up to 200 mW and an offset-coupled laser array with a 4/5 element emits up to 150 mW under pulsed operation. Both laser arrays emit with all elements in-phase locked and produce a single narrow far-field lobe. The full widths at half maximum of the three-element and 4/5-element laser arrays are 5° and 2.5°, respectively. In phase measurements of the lobe of the 4/5-element laser array, we find that the root-mean-square aberration is less than 0.11λ under pulsed operation. This phase aberration is constant with varying power from 75 to 150 mW.

Notes: We have developed a high-power, semicylindrical-shaped waveguide inner stripe laser diode (SCILD) using a current confinement structure. The structure is optimized for high-power operation without catastrophic optical damage (COD) which limits the maximum available optical power. We confirm that the optical electric field shape in the LD waveguide layer obtained from our analysis coincides with the micrograph of the COD on the device facet. The SCILD is emitted in the fundamental transverse mode up to 190 mW. The full beam angles between the half-power points were 10° and 30° in the directions parallel and perpendicular to the junction plane, respectively. The characteristic temperature of the threshold current was 152 K.

Notes: GaAs was found to react directly with hydrogen at temperatures above 800 °C. This reaction resulted in etching of GaAs. An etching rate of 10–15 A(ring)/min was observed after annealing at 900 °C in a H2/AsH3 ambient. On the other hand, no etching was observed after annealing in an Ar/AsH3 ambient. The etching rate was found to be proportional to the pressure of H2 to the 3/2 power. A smooth mirrorlike surface was obtained under excess As pressure, due to the resulting congruent loss of Ga and As. An Arrhenius plot of the etching rate gives an energy of 2.90 eV, which is in good agreement with the heat of evaporation of Ga, which indicates that the etching rate is determined by the rate of evaporation of Ga atoms at the surface.

Notes: Current–voltage characteristics of GaAs/AlxGa1−xAs /GaAs heterobarriers grown by metalorganic chemical vapor deposition were investigated for x from 0.32 to 0.46. Calculation of the current, which included just two components—a tunneling component and a thermionic component—agreed well with experimental results. The tunneling effective mass used is the same as the Γ point effective mass when x is 0.32; this value allows the calculated results to fit the experimental data. The tunneling effective mass becomes much larger than the Γ point mass as x increases. This fact suggests that the other band edge X participates in the tunneling process, making the effective mass larger as it approaches the Γ point edge. The barrier heights deduced from I–V and I–T relations are in good agreement. The results support a ratio of 60%–65% of AlGaAs/GaAs conduction-band discontinuity to the total band-gap difference.