Chiaki Kojima

Carbon incorporation in metalorganic chemical vapor deposition (Al,Ga)As films grown on (100), (311)A, and (311)B oriented GaAs substrates

The amount of carbon in GaAs and (Al,Ga)As films depends on the orientation of crystals grown by metalorganic chemical vapor deposition. We investigated the relation between the incorporation of carbon and the orientation of crystals using (100), (311)A, and (311)B substrates. The concentration of electrons on (311)B substrates of unintentionally doped films was higher than those of the films on (100) and (311)A substrates. The films grown on (311)B substrates did not show p‐type behavior even when they were grown with a fairly low V/III ratio. The relative intensity of the free‐to‐carbon acceptor luminescence of the films grown on (311)B substrates was smaller than that of films grown on the other substrates. This is consistent with the results of carbon contamination indicated by secondary ion mass spectra. Furthermore, a reduced peak in photoluminescence caused by defects was observed when (311)B substrates were used.

680-nm band GaInP/AlGaInP tapered stripe laser

A gain‐guiding tapered stripe laser was fabricated using a Ga0.5In0.5P/(Al0.5Ga0.5)0.5In0.5P double heterostructure wafer grown by metalorganic chemical vapor deposition. The laser showed a continuous wave (cw) threshold current of 48 mA, a maximum temperature for cw operation of 81 °C, an aspect ratio of about 2, and an astigmatism near 25 μm. The emission wavelength was 684 nm. Thirty‐two devices have been operating without significant degradation for more than 2000 h at 50 °C with a constant output power of 3 mW.

AlGaAs/GaAs distributed feedback laser diodes grown by MOCVD

Abstract AlGaAs/GaAs distributed feedback (DFB) laser diodes emitting at 880 and 760 nm were fabricated by a two-step MOCVD growth technique. Epitaxial growth was carried out in a conventional atmospheric-pressure MOCVD system with a vertical reactor. A mesa-stripe geometry and separate-confinement heterostructure (SCH) was employed for the laser structure. The cladding layer ( x = 0.35, 0.48) was successfully regrown on the guiding layer ( x = 0.15, 0.25) corrugated with a 0.25 μm period (2nd order grating). Continuous wave (CW) operations were achieved up to 53°C for devices emitting at 880 nm and up to 10°C for devices emitting at 760 nm. A threshold current as low as 55 mA was obtained for a device emitting at 880 nm under CW operation at room temperature.

Magnesium doping of (Al,Ga)As in metalorganic chemical vapor deposition

Magnesium doping of AlxGa1−xAs in metalorganic chemical vapor deposition and the properties of the grown layer have been investigated. Bis‐cyclopentadienylmagnesium, CP2Mg, was used as a precursor of Mg. The hole concentration increased linearly from 3.5×1016 to 1×1019 cm−3 when the ratio of CP2Mg to trimethylgallium was increased. The carrier concentration increased with the increase of Al concentration, decreased with the increase of growth temperature, and was independent of the ratio of arsine to column III elements, V/III. The photoluminescence (PL) intensity increased when the growth temperature was increased and/or the V/III ratio was increased. The intensity of a deep PL band associated with near band‐edge emission, usually seen in the low‐temperature PL spectra of Zn‐doped (Al,Ga)As, was smaller than that in Zn‐doped (Al,Ga)As. The activation energy of the Mg acceptor deduced from the temperature dependence of the carrier concentration was smaller than that of the Zn acceptor.

Photoluminescence study on the interface of a GaAs/AlxGa1−xAs heterostructure grown by metalorganic chemical vapor deposition

The interface of a GaAs/AlxGa1−xAs heterostructure grown by metalorganic chemical vapor deposition has been studied by photoluminescence spectroscopy by using a step‐etching technique. Luminescence peaks associated with vacancy complexes emitted from both GaAs and AlxGa1−xAs layers were observed, and these peaks were remarkably intense on both sides of the GaAs/AlxGa1−xAs interface region. This result can be explained by the accumulation of vacancies in the interface region. The cause of this vacancy accumulation at the interface is discussed.

Ohmic contacts on selectively doped AlInAs/GaInAs heterostructures using Ni, AuGe and Au

Abstract We studied three different ohmic metals, AuGe-Ni, Ni-AuGe-Au and AuGe-Au, to find the most suitable one for use in selectively doped AlInAs/GaInAs heterostructures. In the past, AuGe-Ni has been the most commonly used metallic structure. However, AuGe-Ni shows a high contact resistance of about 0.2 Ωmm. Using Ni-AuGe-Au, we were able to obtain a low ohmic contact resistance of about 0.1 Ωmm by optimizing the thickness of the Ni layer and the alloying temperature. This resulted, however, in alloyed layers penetrating the semiconductor deeply. More acceptable results were obtained using AuGe-Au, which provided shallow alloyed layers and good surface morphology in addition to a low contact resistance of about 0.1 Ωmm in a wide range of alloying temperatures from 300 to 450°C. Thus we conclude that a simplified structure without Ni is the preferable ohmic metal for selectively doped AlInAs/GaInAs heterostructures.

AlGaAs/GaAs distributed feedback lasers with first‐order grating fabricated by metalorganic chemical vapor deposition

Distributed feedback AlGaAs/GaAs lasers with first‐order grating (1295 A) were fabricated and successfully operated under continuous wave conditions at room temperature. A coupling coefficient of 115 cm−1 and a threshold current of 47 mA were obtained. A stable single‐mode oscillation was maintained up to 100 °C.

AlGaInP Visible Semiconductor Lasers

The device characteristics of 680nm-band gain-guiding AlGaInP ion-implanted stripe double-heterostructure lasers with a GaInP active layer are presented. A narrow stripe laser with a stripe width of 8 µm showed a low threshold current of 68 mA, continuous-wave (cw) operation at a temperature as high as 68°C and a lifetime more than 3000 hours. The maximum light output power under cw operation was increased from 22 mW/facet to 250 mW/facet by broadening the stripe width to 60 µm. Two methods of shortening the emission wavelength are also discussed.

In-Line Holographic Lenses of High Numerical Aperture

In-line holographic lenses of numerical aperture of 0.4 and 0.55 were successfully fabricated for the purpose of the application to an optical disk player with a He-Ne laser. They were recorded at 6471 A in the methylene-blue sensitized dichromated gelatin film of 15 µm in thickness. The special design of the optical recording system and the careful processing of the recording materials were required. The evaluations of the modulation transfer function, the focused beam profile, the average diffraction efficiency and the stability test were performed. Bragg and Raman Nath diffractions occurred in the hologram were also investigated to explain the observed results.

Yield dependency on length of AlGaAs/GaAs second‐order distributed feedback lasers with cleaved facets

The effect of length on the yield of second‐order distributed feedback lasers with cleaved facets capable of operating in a single longitudinal mode and on their characteristics has been studied experimentally. The optimum length of 200 μm was determined in reference to the coupling coefficient and the end‐facet reflectivity. A yield of more than 70% was obtained for lasers 200 μm in length capable of operating at a level of at least 10 mW and over.