2004 Fiscal Year Final Research Report Summary
In-situ measurements of the irradiation effects in semiconductors under high energy ion irradiation
| Project/Area Number |
14380233
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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 |
Nuclear engineering
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| Research Institution | Tohoku University (2003-2004)
The University of Tokyo (2002) |
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Principal Investigator |
ASAI Keisuke Tohoku University, Graduate School of Engineering, Professor, 大学院・工学研究科, 教授 (60231859)
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| Co-Investigator(Kenkyū-buntansha) |
IWAI Takeo The University of Tokyo, Research Center for Nuclear Science and Technology, Research Associate, 原子力総合研究センター, 助手 (30272529)
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| Project Period (FY) |
2002 – 2004
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| Keywords | high-density excitation / ion beam / time-resolved luminescence spectrum / MgO / electron-hole plasma / CdS / layered perovskite-type compound / multiple quantum-well structure |
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| Research Abstract |
We analyzed the high-density excitation effects and local high temperature state induced by energetic ions in various semiconductors by measuring the luminescence spectra under irradiation. Time-integrated luminescence spectra were measured with an OMA. Time-resolved spectra were measured with a time-correlated. single photon counting system, which determined the arrival time of ions by detecting with multichannel plates the secondary electrons emitted when the ions transmit a carbon foil.
At first, we have succeeded in observing the transient local high-temperature state along an ion trajectory by measuring the luminescence spectra of organic-inorganic layered perovskite materials, which is known to form a natural multiple quantum well structure and exhibit fast luminescence due to free excitons. Furthermore, from the relation between the observed local temperature and the excitation density, it was found that local melting occurs.
Secondly, we analyzed the spatial behavior of the excit
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ed carriers from the time-resolved luminescence spectra of CdS. By analyzing the spectral shape of a fast aluminescence band due to electron-hole plasma, we estimated the density and the average energy of the excited carriers when radiative recombination occurs. The obtained results can be quantitatively explained within the diffusion model where polar optical scattering of the excited carriers is taken into account.
In addition, we measured the luminescence spectra of a single crystal of MgO, in which the electron lattice coupling is slightly stronger than in semiconductors. As the excitation density increased, a luminescence band due to free excitons reduced its intensity, and finally disappeared. In contrast, another luminescence band appeared at the low-energy side of the free exciton band. Similarly to the case of conventional semiconductors, we attributed the disappearance of the free exciton band and the appearance of the new band to the screening of the Coulomb interaction and the radiative recombination in the collective excited states analogous to the electron hole plasma, respectively. Less
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