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281 results on '"Isu, Toshiro"'

12. Surface Emitting Devices Based on a Semiconductor Coupled Multilayer Cavity for Novel Terahertz Light Sources (Special Section on Fabrication Technologies Supporting the Photonic/Nanostructure Devices)

Author

Kitada, Takahiro, Ota, Hiroto, Lu, Xiangmeng, Kumagai, Naoto, and Isu, Toshiro

Subjects
two-color lasing, coupled multilayer cavity, terahertz source, Physics::Optics, frequency conversion
Abstract

Compact and room-temperature operable terahertz emitting devices have been proposed using a semiconductor coupled multilayer cavity that consists of two functional cavity layers and three distributed Bragg reflector (DBR) multilayers. Two cavity modes with an optical frequency difference in the terahertz region are realized since two cavities are coupled by the intermediate DBR multilayer. In the proposed device, one cavity is used as the active layer for two-color lasing in the near-infrared region by current injection and the other is used as the second-order nonlinear optical medium for difference-frequency generation of the two-color fundamental laser light. The control of the nonlinear polarization by face-to-face bonding of two epitaxial wafers with different orientations is quite effective to achieve bright terahertz emission from the coupled cavity. In this study, two-color emission by optical excitation was measured for the wafer-bonded GaAs/AlGaAs coupled multilayer cavity containing self-assembled InAs quantum dots (QDs). We found that optical loss at the bonding interface strongly affects the two-color emission characteristics when the bonding was performed in the middle of the intermediate DBR multilayer. The effect was almost eliminated when the bonding position was carefully chosen by considering electric field distributions of the two modes. We also fabricated the current-injection type devices using the wafer-bonded coupled multilayer cavities. An assemble of self-assembled QDs is considered to be desirable as the optical gain medium because of the discrete nature of the electronic states and the relatively wide gain spectrum due to the inhomogeneous size distribution. The gain was, however, insufficient for two-color lasing even when the nine QD layers were used. Substituting two types of InGaAs multiple quantum wells (MQWs) for the QDs, we were able to demonstrate two-color lasing of the device when the gain peaks of MQWs were tuned to the cavity modes by lowering the operating temperature.

Published
2017

13. Reactive ion etching of InP using C2H6/H2/O2

Author

Sugimoto, Hiroshi, Ohtsuka, Ken-ichi, Isu, Toshiro, Tada, Hitoshi, Miura, Takeshi, and Shiba, Tetsuo

Subjects
Crystals -- Etching, Oxygen -- Research, Semiconductors -- Research, Physics
Abstract

Reactive ion etching of InP using a C2H6/H2/O2 mixture was investigated. In addition, the effects of O2 addition to the C2H6/H2 gas was studied. The results showed that the addition of oxygen gas to the base mixture produced an extremely smooth etched surface. The oxygen gas significantly decreased hydrocarbon polymer formation during the etching process and reduced the roughness of the etched surface.

Published
1992

17. Observation of quantum beat oscillations and ultrafast relaxation of excitons confined in GaAs thin films by controlling probe laser pulses.

Author

Ohta, Shohei, Kojima, Osamu, Kita, Takashi, and Isu, Toshiro

Subjects
EXCITON theory, GALLIUM arsenide, THIN films, ULTRASHORT laser pulses, OSCILLATIONS, QUANTUM wells, CENTER of mass, HETEROSTRUCTURES
Abstract

We study the quantum beats and relaxation dynamics of exciton center-of-mass motion confined in GaAs thin films by a reflection-type pump-probe technique. By using spectrally narrowed probe pulses with energies comparable with the exciton energy separation, oscillations caused by quantum beats between the confined excitons and ultrafast responses which are shorter than their lifetime appear. This appearance of quantum beats does not result from the so-called detection process. Our results demonstrate that the reduction of the destructive interference of the probe pulse in the sample is a key factor to observe the excitonic quantum beats. [ABSTRACT FROM AUTHOR]

Published
2012
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18. Depolarization effect on optical control of exciton states confined in GaAs thin films.

Author

Yamashita, Takae, Kojima, Osamu, Kita, Takashi, and Isu, Toshiro

Subjects
GALLIUM arsenide, THIN film research, SOLID state electronics, SEMICONDUCTOR research, NANOSTRUCTURED materials
Abstract

We report the effects of depolarization on the excitonic Rabi oscillation in GaAs thin films measured in the 2k1-k2 direction of a degenerate four-wave-mixing signal. The Rabi frequency, measured by changing the k2 pulse intensity, varies with the k1 pulse intensity; the Rabi frequency decreases with an increase in the k1 power. This decrease originates from the reduction in the field intensity of the k2 pulse, which consists of the local field and depolarization terms. Cancellation of the k2 field due to depolarization leads to the decrease in the Rabi frequency. [ABSTRACT FROM AUTHOR]

Published
2011
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23. Current-injection two-color lasing in a wafer-bonded coupled multilayer cavity with InGaAs multiple quantum wells

Author

Minami, Yasuo, Ota, Hiroto, Lu, Xiangmeng, Kumagai, Naoto, Kitada, Takahiro, Isu, Toshiro, Minami, Yasuo, Ota, Hiroto, Lu, Xiangmeng, Kumagai, Naoto, Kitada, Takahiro, and Isu, Toshiro

Abstract

Current-injection two-color lasing has been demonstrated using a GaAs/AlGaAs coupled multilayer cavity that is a good candidate for novel terahertz-emitting devices based on difference-frequency generation (DFG) inside the structure. The coupled cavity structure was fabricated by the direct wafer bonding of (001)- and (113)B-oriented epitaxial wafers for the efficient DFG of two modes in the (113)B side cavity, and two types of InGaAs multiple quantum wells (MQWs) were introduced only in the (001) side cavity as optical gain materials. The threshold behavior was clearly observed in the current–light output curve even at room temperature. Two-color lasing was successfully observed when the gain peaks of MQWs were considerably tuned to the cavity modes by the operating temperature.

Published
2017

24. Two-color surface-emitting lasers using a semiconductor coupled multilayer cavity

Author

Kitada, Takahiro, Ota, Hiroto, Lu, Xiangmeng, Kumagai, Naoto, Isu, Toshiro, Kitada, Takahiro, Ota, Hiroto, Lu, Xiangmeng, Kumagai, Naoto, and Isu, Toshiro

Abstract

Two-color surface-emitting lasers were demonstrated, employing a GaAs/AlGaAs coupled multilayer cavity composed of two cavity layers and three distributed Bragg reflector (DBR) multilayers. InGaAs multiple quantum wells (MQWs) with two different well widths were introduced only in the upper cavity, sandwiched between p-type and n-type DBRs. This current-injection type device exhibited two-color lasing in the near-infrared region under room temperature pulsed conditions. This two-color lasing was obtained when the lower cavity had an optimal thickness relative to the upper cavity thickness and the MQW emission properties.

Published
2016

25. Photoconductivity of Er-doped InAs quantum dots embedded in strain-relaxed InGaAs layers with 1.5µm cw and pulse excitation

Author

Murakumo, Keisuke, Yamaoka, Yuya, Kumagai, Naoto, Kitada, Takahiro, Isu, Toshiro, Murakumo, Keisuke, Yamaoka, Yuya, Kumagai, Naoto, Kitada, Takahiro, and Isu, Toshiro

Abstract

We fabricated a photoconductive antenna structure utilizing Er-doped InAs quantum dot layers embedded in strain-relaxed In0.35Ga0.65As layers on a GaAs substrate. Mesa-shaped electrodes for the antenna structure were formed by photolithography and wet etching in order to suppress its dark current. We measured the photocurrent with the excitation of ~1.5 µm cw and femtosecond pulse lasers. Compared with the dark current, the photocurrent was clearly observed under both cw and pulse excitation conditions and almost linearly increased with increasing excitation power in a wide range of magnitudes from 10 W/cm2 to 10 MW/cm2 order.

Published
2016

26. Fabrication of two-color surface emitting device of a coupled vertical cavity structure with InAs quantum dots formed by wafer bonding

Author

Ota, Hiroto, Lu, Xiangmeng, Kumagai, Naoto, Kitada, Takahiro, Isu, Toshiro, Ota, Hiroto, Lu, Xiangmeng, Kumagai, Naoto, Kitada, Takahiro, and Isu, Toshiro

Abstract

We fabricated the two color surface emitting device of a coupled cavity structure which is applicable to terahertz light source. GaAs/AlGaAs vertical multilayer cavity structures were grown on a (001) and (113)B GaAs substrates and the coupled multilayer cavity structure was fabricated by wafer-bonding of them. The top cavity contains self-assembled InAs quantum dots (QDs) as optical gain materials for two-color emission of cavity-mode lights. The bonding position was optimized for the equivalent intensity of two-color emission. We formed a current injection structure, and two-color emission was observed by current injection, although lasing was not observed.

Published
2016

44. Development of type II superlattice detector for future space applications at JAXA

Author

Katayama, Haruyoshi, primary, Murooka, Junpei, additional, Naitoh, Masataka, additional, Imai, Tadashi, additional, Sato, Ryota, additional, Tomita, Eichi, additional, Ueno, Munetaka, additional, Murakami, Hiroshi, additional, Kawasaki, Satoshi, additional, Bito, Kunihiko, additional, Kimata, Masafumi, additional, Kitada, Takahiro, additional, Isu, Toshiro, additional, Patrashin, Mikhail, additional, and Hosako, Iwao, additional

Published
2012
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