| Project/Area Number |
09650359
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Electronic materials/Electric materials
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| Research Institution | Yamaguchi University |
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Principal Investigator |
YAMADA Yoichi Yamaguchi University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (00251033)
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| Project Period (FY) |
1997 – 1998
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| Project Status |
Completed (Fiscal Year 1998)
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| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 1998: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 1997: ¥2,100,000 (Direct Cost: ¥2,100,000)
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| Keywords | wide-gap semiconductor / low-dimensional structure / exciton / biexciton / localization / optical gain / stimulated emission / ZnS / 短波長半導体レーザ / 低次元構造 / 量子井戸 |
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| Research Abstract |
We have studied the localization of biexcitons and the mechanism of optical gain formation in ZnS-based quantum- well structures. The Cd_<chi> Zn_<I-chi> S-ZnS multiple-quantum-well samples used in this work were prepared by a low-pressure metalorganic chemical vapor deposition technique.
By means of photoluminescence excitation spectroscopy, we clearly observed the two-photon absorption process of biexcitons, which was the direct creation of biexcitons from the ground state. On the basis of the energy difference between the one-photon exciton resonance and the two-photon biexciton resonance, the binding energy of biexcitons was obtained for a series of samples with various Cd composition ratios and well-layer thicknesses. The maximum value of the biexciton binding energy obtained to date was estimated to be 34 meV.This value is approximately four times as large as the binding energy of the biexciton in ZnS, and exceeds the thermal energy of 26 meV at room temperature. it was also noted that the detected-photon-energy dependence of the two-photon biexciton resonance clearly indicated the localization of biexcitons.
Temperature dependence of stimulated emission processes was also investigated by means of optical pumping experiments. We observed the ultraviolet stimulated emission just at the energy position of the biexcilon lnminescence and found that the threshold excitation-power density for the stimulated emission was almost constant up to about 240 K.This result strongly indicates that the optical gain formation due to the radiative recombination process of biexcitons is achieved up to about 240 K.We also found that the degree of biexciton localization was not effective to lower the threshold excitation-power density for stiumlated emission. In order to realize the biexcitonic optical gain formation at room temperature, we consider that further increase in the biexciton binding energy is essential.
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