Hiroharu Sugawara

High net modal gain (>100 cm −1 ) in 19-stacked InGaAs quantum dot laser diodes at 1000 nm wavelength band

An InGaAs quantum dot (QD) laser diode with 19-stacked QDs separated by 20 nm-thick GaAs spacers was fabricated using an ultrahigh-rate molecular beam epitaxial growth technique, and the laser characteristics were evaluated. A 19-stacked simple broad area QD laser diode was lased at the 1000 nm waveband. A net modal gain of 103 cm(-1) was obtained at 2.25 kA/cm(2), and the saturated modal gain was 145.6 cm(-1); these are the highest values obtained to our knowledge. These results indicate that using this technique to highly stack QDs is effective for improving the net modal gain of QD lasers.

Relationship of Surface Tension, Oxygen Partial Pressure, and Temperature for Molten Iron

Surface tension of molten iron was measured under reducing gas atmosphere of Ar–He–5 vol % H2 by an oscillating droplet method using electromagnetic levitation. The temperature dependence of surface tension did not exhibit a linear relationship but revealed a peculiar kink at around 1810 K, due to competition between the temperature dependence of oxygen partial pressure and that of the oxygen adsorption equilibrium constant. We successfully derived the surface tension of molten iron as functions of both oxygen partial pressure and temperature. Furthermore, the standard enthalpy and entropy for oxygen adsorption reaction on molten iron were also estimated.

Gain Measurement of Highly Stacked InGaAs Quantum Dot Laser with Hakki?Paoli Method

A 147-µm-long cavity laser diode with 19 InGaAs quantum dot layers was fabricated by the ultrahigh-rate molecular beam epitaxial growth technique, and its gain properties were investigated using the Hakki–Paoli method below the threshold current (Ith) of 111.5 mA. At an injection current of 100.3 mA (0.9Ith), the positive net modal gain was in the range between 1005 and 1043 nm, corresponding to a photon energy of 45 meV. The maximum net modal gain and maximum modal gain were 46.5 and 60.5 cm-1, respectively. A differential net modal gain of as high as 3.8 cm-1/mA was observed at 0.77 times the threshold current. No gain saturation appeared below the threshold current, and injection currents higher than 78.4 mA (≈0.7Ith) were required to obtain a net modal gain.

99-μm-long-cavity laser diode using highly stacked InGaAs quantum dots

We fabricated a 99-μm-long-cavity broad-area laser diode involving 19 stacked InGaAs quantum dots, which lased at 1013 nm without any HR coating, and the threshold current density was 2.25 kA/cm2.

Energetic consideration of compounds at Mg2Si–Ni electrode interlayer produced by spark-plasma sintering

In order to understand the presence of the MgNi2-type phase, the η-phase, and the ω-phase at the boundary layer produced by the simultaneous spark plasma sintering of mixed Ni and Mg2Si powders, we have calculated the electronic energies of these phases. The phase change of MgNi2 X Si2(1− X ) from the Cu2Mg-type to the MgNi2-type through the Fe2Tb-type structures with increases in X, as observed by Song and Varin [Metall. Mater. Trans. A 32, 5 (2001)], is well-reproduced by the present calculations. The stability of the η-phase (Mg6Ni16Si7) is also explained, but that of the ω-phase is not explained by the energetic calculations, even if the entropy effect of mixing is assumed.

Time-Resolved Photoluminescence Study of InGaAs Quantum Dot Structure Prepared by Ultrahigh-rate Molecular Beam Epitaxial Growth Technique

Time-resolved photoluminescence spectroscopy of InGaAs strained quantum dot prepared by ultrahigh-rate MBE growth indicated a small distribution of ground states energies and carrier lifetime as long as 0.9 ns at 77 K.

Characterization of 24 stacked InGaAs quantum dot laser fabricated by ultrahigh-rate MBE growth technique

Highly stacked of 24 InGaAs/GaAs quantum dot laser was prepared using ultrahigh-rate MBE growth technique and observed laser emission at 1070nm, and its internal quantum efficiency evaluated to be 22.0%.

High threshold modal gain based on highly stacked InGaAs quantum dot laser diode

A threshold modal gain of up to 103 cm-1 was observed for 19-stacked InGaAs quantum dot (QD) laser diodes with a high QD volume density.