Nozomu Watanabe

Epitaxially Induced Stress in GaAs Layer on V-Grooved Si and GaAs Substrates

Raman spectra from the (01) face in GaAs epitaxial layers on both V-grooved (100)-Si and -GaAs substrates were observed. Peak- shifts in the transverse-optical (TO) modes at the edge of the V-groove were observed in hetero- and homo-epitaxial structures, respectively. Additional line broadening in the TO mode was only observed in the heteroepitaxial structure. The peak-shifts result from the epitaxially induced stress and the additional broadening was due to the fluctuation of the stress.

Structure study of Au–GaAs(001) interfaces by HEIS, XPS, and RHEED

MeV He+ ion scattering/channeling (HEIS), angle resolved XPS, and RHEED have been applied to study the Au and MBE‐grown GaAs(001)‐c(4×4) interface structures in the Au film thickness range of ≲70 A and the annealing temperature range from room temperature up to ∼300 °C. The results show release of the As atoms and epitaxial growth of the Au film even at room temperature. The shrinked Au film after annealing displays selective registry to the [110] direction, which is believed to result from a strong Au–GaAs(001) interaction.

Surface Defect Formation in GaAs Layers Grown on Intentionally Contaminated Substrate by Molecular Beam Epitaxy

The origin of oval defects of GaAs layers grown by molecular beam epitaxy (MBE) has been studied using intentionally contaminated GaAs substrates. Diamond and Al2O3 particles, and Ga and In droplets are used as contaminants. The surface defect shape caused by the particles is very similar to that of oval defects in our MBE grown layers which have a pit in the middle. This is strong evidence that one of the origins of the oval defects is a nonreactive and nonvolatile small particle. The shape of surface defects due to Ga or In droplets is different from that due to diamond or Al2O3 particles in that the former do not have a pit. Oval defects with a pit in MBE grown layers cannot be ascribed to the group III droplets spit out from effusion cells.

Studies of Au‐GaAs (001) interfaces prepared by molecular beam epitaxy. II. Thermal stability of Au‐GaAs (001) interface

Au/GaAs (001) interface reactions due to annealing have been studied using the XPS, RHEED, SEM, RBS, EPMA, and AES methods. The samples were prepared by Au deposition on MBE‐grown GaAs (001)‐c(4×4) surfaces at room temperature. The Au films were epitaxially grown twin crystals, about 50 A thick. Two phenomena were observed: Au shrinkage and erosion of GaAs by Au. The Au shrinkage occurs in the early stage of annealing. Rectangular or connected rectangular GaAs surfaces are exposed due to Au shrinkage. The sides of these rectangular surfaces are parallel to the GaAs 〈110〉 and 〈110〉 directions. The higher the annealing temperatures, the greater the Au shrinkage and erosion of GaAs by Au. For the sample annealed at 450 °C for 3 h, Au‐Ga alloy agglomerates formed on the GaAs (001) and GaAs (111) B surface. The one‐dimensional disordered structure was observed by RHEED for the sample annealed at 305 °C for 14 h. The Au crystal quality is improved by annealing at temperatures above 100 °C.

High-power operation of 830-nm AlGaAs laser diodes

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.

Studies of Au‐GaAs (001) interfaces prepared by molecular beam epitaxy. I. Overlayer growth and Schottky barrier formation

Evolution of Au‐GaAs (001) interface structures with increasing Au exposure was studied. This study utilized photoelectron spectroscopy, electron diffraction, and He‐ion Rutherford backscattering spectrometry. This was accomplished with the aid of molecular‐beam epitaxy for surface preparation. The thermal stability of Au‐GaAs (001) interfaces are presented in the following paper [N. Watanabe, K. L. I. Kobayashi, T. Narusawa, and H. Nakashima, J. Appl. Phys. 58, 3766 (1985)]. New phenomena were observed on overlayer growth, electronic structure change, and Schottky barrier formation. The present results apparently differ from previous Au‐GaAs (110) system results; however, they support the surface defect model for Schottky barrier formation by W. E. Spicer, I. Lindau, P. Skeath, C. Y. Su, and P. Chye [Phys. Rev. Lett. 44, 420 (1980)].

Selective growth and optical properties of an AlGaAs layer on V‐grooved Si substrates

Selective growth and optical properties of GaAs and AlXGa1−X As (X≂0.3) layers on V‐grooved Si substrates by low‐pressure metalorganic vapor‐phase epitaxy are studied. In the microscopic Auger electron spectroscopy measurement, the As and Ga atoms were not observed on the {111} Si sidewalls of the V‐grooved Si substrates. This result clarifies that the GaAs and AlXGa1−X As layers grew only on the {100} planes. The cross‐sectional shapes of the selectively grown layer depended on the crystal directions due to the different chemical reactions on the different planes. Spectra of the microscopic photoluminescence and Raman scattering measurements from selectively grown layers showed the significant positional dependence. These spectral changes are interpreted as the impurity and/or the strain distributions in the selectively grown layers.

Supermode control and phase front measurements of phase‐locked offset‐coupled laser arrays with a large optical waveguide structure

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.

Low-Phase-Aberration Output of 830 nm AlGaAs Offset-Coupled Laser Arrays

Phase-locked lasers with refractive-index waveguides have been developed. The elemental stripes of the laser are evanescently and offset coupled. A fundamental supermode operation in the 2/3-element laser arrays is achieved. The phase aberration is less than λ/14 (λ=830 nm). The output power of the laser array increases almost linearly up to 200 mW with an external differential slope efficiency of 0.75 W/A.

Molecular Beam Epitaxial Growth of InxGa1-xAs and InxAl1-xAs on Si Substrates

Surface morphologies of InxGa1-xAs and InxAl1-xAs (X~0.53) layers grown on Si (100) substrates by molecular beam epitaxy are investigated. It is found that the InxAl1-xAs/InxGa1-xAs multiquantum wells buffer layer and the substrate misorientation play an important role in the reduction of the surface roughness. The surface morphologies of InxGa1-xAs and InxAl1-xAs on Si compare well with that of GaAs on Si.