| Project/Area Number |
11450028
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| Research Category |
Grant-in-Aid for Scientific Research (B).
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Applied optics/Quantum optical engineering
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| Research Institution | Yokohama National University |
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Principal Investigator |
TADA Kunio Yokohama National Univ., Faculty of Engineering, Professor, 工学部, 教授 (00010710)
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| Co-Investigator(Kenkyū-buntansha) |
NOH Joo-hyong Yokohama National Univ., Faculty of Engineering, Research Associate, 工学部, 助手 (50313474)
ARAKAWA Taro Yokohama National Univ., Faculty of Engineering, Associate Professor, 工学部, 助教授 (40293170)
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| Project Period (FY) |
1999 – 2000
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| Project Status |
Completed (Fiscal Year 2000)
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| Budget Amount *help |
¥14,600,000 (Direct Cost: ¥14,600,000)
Fiscal Year 2000: ¥4,900,000 (Direct Cost: ¥4,900,000)
Fiscal Year 1999: ¥9,700,000 (Direct Cost: ¥9,700,000)
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| Keywords | Potential-tailored quantum well / Five-layer asymmetric coupled quantum well (FACQW) / Optical modulator / Optical switch / Electrorefractive index change / Molecular beam epitaxy (MBE) / Migration enhanced epitaxy (MEE) / Layer thickness fluctuation / 光変調デバイス / 電界誘起屈折率変化 |
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| Research Abstract |
The five-layer asymmetric coupled quantum well (FACQW) structure, in contrast to the conventional rectangular quantum well (RQW), can produce very large electrorefractive index change Δn in the transparency wavelength region far from the absorption edge. We theoretically and experimentally studied fabrication of high-quality GaAs/AlGaAs FACQWs and their application to optical modulators and switches.
1. Fabrication and Characterization of the FACQW structures
The FACQWs were grown by molecular beam epitaxy (MBE) with precise shutter control.
Photoluminescence and photocurrent measurements of the samples revealed that the structures were fabricated as designed and their Δn characteristucs were consistent with calculation results.
2. Influence of layer thickness fluctuation on electrorefractive index change of the FACQW
The influence of 1 ML thickness deviations and fluctuations from the designed FACQW structure on Δn was studied theoretically.
i) The thickness variation of the thicker GaAs we
… More
ll layers in the FACQW has a considerable influence on Δn. The influence of the two thin Al(Ga)As barrier layers is small compared with that of other GaAs well layers.
ii) The ratio of the thicknesses of the two thicker GaAs layers significantly affects the Δn, characteristics of the FACQW.The value Δn does not change as long as the ratio of the thicknesses of the layers is kept constant.
iii) The physical origin of the sharp dip in the Δn-electric field characteristic was studied theoretically. The dip can be removed by changing the position or Al content of the thin AlGaAs barrier layer for potential modification.
iv) The influence of the statistical fluctuation of the layer thickness by 1 ML on the Δn characteristics was discussed. Even when An decreases with the increase of the occurrence probability of a layer being thicker or thinner by 1 ML (the ratio of well area with deviated thicknesses to total area of the layer), the FACQW still maintains a much larger Δn than the conventional rectangular quantum wells (RQWs).
3. Growth of high-quality quantum well structures with migration enhanced epitaxy method
The migration enhanced epitaxy (MEE) method is a promising growth technique that can obtain flatter and steeper heterointerfaces at lower growth temperature than conventional MBE.We introduced the MEE method to growth of high-quality quantum well structures.
i) A computer-controlled system of K-cell shutters was installed for complicated gowth
sequence of MEE.
ii) K-cell shutter sequence for AlGaAs growth was investigated. We found the sequence that after Al and Ga atoms are supplied simultaneously, Ga and As atoms are supplied alternatively can realize flatter heterointerface without Al content fluctuation. Utilizing this sequence, high-quality RQWs were successfully grown at 500℃.
4. Electrorefrative effect in a modified FACQW
A modified FACQW has a slightly different structure from the normal FACQW, and it is expected to obtain very large negative Δn. We theoretically studied in detail electrorefrative effect in the modified FACQW.We discussed the detailed mechanism of large Δn in the modified FACQW.In addition, we found that the modified FACQW has more tolerance of layer thickness fluctuation than the normal FACQW. Less
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