Mitsuru Ekawa

Quantum-Dot Semiconductor Optical Amplifiers With Polarization-Independent Gains in 1.5-

We have demonstrated a polarization-independent gain in semiconductor optical amplifiers that have columnar quantum dots surrounded by strained side barriers in 1.5-mum wavelength bands. We obtained a polarization-dependent gain of 0.5 dB with a gain of 10 dB and a saturation output power of 18 dBm at a wavelength of 1.55 mum.

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The growth mechanism and electrical characteristics of (100) CdTe layers grown on (100) GaAs by low-pressure organometallic vapor phase epitaxy have been reported. The growth mechanism changed around the growth temperature of 400°C. Adduct pyrolysis dominated the growth below the temperature of 400°C. Above this temperature, a pyrolysis of DETe dominated the growth. High-quality p-type layers were obtained when the layers were grown thicker than 2 µm at 420°C. The hole density and the Hall hole mobility were in the ranges of 2.2-3.5×1015 cm-3 and 60–100 cm2/V·s, respectively. In contrast to this, the grown layer became semi-insulating when the thickness was less than 2 µm due to out-diffusion of Ga from the substrates. The double crystal X-ray rocking curve also showed a FWHM value of 155 arcsec at the thickness of 6 µm.

m Wavelength Bands

X‐ray photoelectron spectroscopy and Auger electron spectroscopy measurements were performed to investigate the initial growth mechanism and the selection of growth orientations of CdTe layers grown on (100) GaAs by metalorganic vapor phase epitaxy (MOVPE). The surface stoichiometry of the GaAs substrate was found to recover when annealed in a H2 flow atmosphere (500 °C, 5 min), although the surface was initially in an As‐rich condition after chemical etching by H2SO4: H2O2: H2O=5: 1: 1. No oxide was observed at both the etched and H2 annealed GaAs surfaces. Preferential adsorption of Te occurred on the GaAs surface when H2 annealing was carried out in the growth reactor in the presence of residual CdTe deposits. One monolayer of Te with a thickness of about 1.8 A was adsorbed on the GaAs surface when the H2 annealed GaAs was exposed to diethyltelluride during the cooling period from the annealing temperature to the growth temperature (420 °C). On the other hand, minimal adsorption of Cd occurred when the...

Growth Characteristics and Electrical Properties of (100) CdTe Layers Grown on (100) GaAs by Low-Pressure Organometallic Vapor Phase Epitaxy

The As doping mechanism in (100) CdTe layers grown on (100) GaAs by atmospheric‐pressure metalorganic vapor phase epitaxy was studied. Triethylarsine (TEAs) was used as a dopant source. The source materials used were dimethylcadmium (DMCd) and diethyltelluride (DETe). The As incorporation was enhanced by decreasing the DETe flow rate under a fixed DMCd flow condition, and by lowering the growth temperature. Assuming 100% activation of As, the As incorporation efficiency was estimated to be about 0.1%. The As incorporation was dominated by the sticking rate of the As species onto the Cd species. The hole concentration was controlled from 2×1015 to 3×1016 cm−3 in proportion to the TEAs flow rate below 1×10−7 mol/min. Those doped layers showed hole mobilities as high as 75 cm2/V s. Low‐temperature photoluminescence (PL) studies revealed that a neutral‐acceptor bound‐exciton at 1.5901 eV is due to a substitutional As acceptor on the Te site. The As ionization energy was about 90 meV from the PL and electrical...

X-ray photoelectron spectroscopy and Auger electron spectroscopy analyses of the initial growth mechanism of CdTe layers on (100) GaAs by metalorganic vapor phase epitaxy

This paper describes the optimum design, fabrication, and performance of a 1.3-/spl mu/m multiple-quantum-well (MQW) laser diode monolithically integrated with a tapered thickness spot-size transformer. The dependence of the lasing characteristics on the thickness distribution of the core layer and on the current injection profile of the device were analyzed. This integrated laser with its optimized structure performed at a low threshold current of 22.2 mA, even at 85/spl deg/C. The integrated spot-size transformer effectively reduced the lateral and vertical far-field FWHMs to 8/spl deg/ and 9/spl deg/, respectively. A very long lifetime of over 1/spl times/10/sup 5/ h was estimated at 85/spl deg/C and 8 mW under CW operation.

Mechanism of arsenic incorporation and electrical properties in CdTe layers grown by metalorganic vapor phase epitaxy

Variations of the GaAs surface conditions and the adsorption of the precursor elements of Cd and Te on the (100)GaAs substrate were studied by x‐ray photoelectron spectroscopy at the initial stage of CdTe growth by organometallic vapor phase epitaxy. The stoichiometry of GaAs substrates was found to recover by annealing in the H2 environment (500 °C, 5 min), while the surface was initially in an As‐rich condition after etching with H2SO4:H2O2:H2O (5:1:1). The preferential adsorption of Te on the GaAs surface was also observed. 〈100〉 oriented growth was obtained routinely when the GaAs surface was fully stabilized with Te after the H2 anneal under the above conditions. 〈111〉 oriented growth resulted when dimethylcadmium was first introduced after the anneal.

Narrow-beam divergence 1.3-/spl mu/m multiple-quantum-well laser diodes with monolithically integrated tapered thickness waveguide

Vapor-liquid-solid (VLS) growth of position-controlled InP nanowires (NWs) with 10–100 μm pitches was investigated on SiO2-mask-patterned InP substrates. In addition to the vertical VLS NWs formed by Au catalysts, excess group-III materials that were diffused from the large mask region formed plural inclined NW-like structures from single openings. The introduction of HCl gas during the NW growth was found to remove the excess group-III materials effectively. Vertical InP NWs with minimal tapering were formed by controlling the HCl flow rate while suppressing the formation of tilted NWs. InP NWs having lengths independent of the pattern pitches, which were regulated by the VLS mechanism, were obtained.

X‐ray photoelectron spectroscopy studies of initial growth mechanism of CdTe layers grown on (100)GaAs by organometallic vapor phase epitaxy

rdquoWe developed a broadband polarization-insensitive multiquantum-well (MQW) semiconductor optical amplifier (SOA) for application as an optical switch in broadcast-and-select-type optical packet switching systems. We adopted a GalnNAs-GalnAs MQW structure active layer to decrease the noise figure (NF) around the gain peak wavelength together with a small gain tilt in the C-band. The device exhibited a smaller NF on the shorter wavelength side of the gain peak compared with a GalnNAs strained-bulk SOA. The reduced NF resulted in a large effective gain bandwidth of up to 90 nm (1510-1600 nm). The device also exhibited the small gain tilt (<1.2 dB) and small polarization-dependent gain (<0.8 dB) in the C-band.

Position-controlled InP nanowires with 10–100 μm pitches using Au-deposited SiO2/InP patterned substrates

We investigated the growth rate enhancement in selective area metalorganic vapor phase epitaxy with a new surface boundary condition for the vapor phase concentration of source materials. In our model, the growth rate is proportional to the vapor phase concentration at a distance of the vapor phase mean-free path of source materials from the substrates, and the vapor phase concentration is laterally uniform at the top of the stagnant layer. This model predicts that the growth rate modulation produced by mask-patterning disappears at a specific pressure at which the vapor phase mean-free path reaches the stagnant layer thickness. We controlled the vapor phase mean-free path of trimethylindium in InP growth by varying the growth pressure from 6 to 180 Torr with a fixed total inlet gas flow rate to the reactor. Experiments showed a great reduction of the growth rate enhancement with the decrease in the growth pressure and the growth rate enhancement virtually disappeared at the lowest pressure. We also investigated the dependence of the stagnant layer thickness on the mask design. The experimental stagnant layer thickness related to the typical surface length, such as the period of mask-patterning.

Polarization-Insensitive GaInNAs–GaInAs MQW-SOA With Low Noise Figure and Small Gain Tilt Over 90-nm Bandwidth (1510–1600 nm)

Correlations of surface morphology with the growth characteristics and optimal doping conditions of (100) CdTe layers grown by metalorganic vapor phase epitaxy have been studied. Growths were carried out on (100) GaAs substrates using diethyltellurium (DETe) and dimethylcadmium (DMCd). Pyramidal hillocks characterized the surface morphology at DETe/DMCd flow ratios below unity, where high p-type doping by arsenic was achieved. By increasing the DETe/DMCd flow ratio from 1 to 2, the surfaces started to show smooth and specular morphologies, where high n-type doping by gallium was achieved. For DETe/DMCd flow ratios exceeding 2, the surfaces changed to show ellipse-like pits which were considered to be due to Te precipitate.