2002 Fiscal Year Final Research Report Summary
STUDY OF POINT DEFECTS IN GaN AND RELATED COMPOUND SEMICONDUCTORS BY MEANS OF POSITRON ANNIHILATION
| Project/Area Number |
13650332
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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 | UNIVERSITY OF TSUKUBA |
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Principal Investigator |
UEDONO Akira UNIVERSITY OF TSUKUBA, INSTITUTE OF APPLIED PHYSICS, ASSOCIATE PROFESSOR, 物理工学系, 助教授 (20213374)
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| Co-Investigator(Kenkyū-buntansha) |
CHICHIBU Shigefusa UNIVERSITY OF TSUKUBA, INSTITUTE OF APPLIED PHYSICS, ASSOCIATE PROFESSOR, 物理工学系, 助教授 (80266907)
AKIMOTO Katsuhiro UNIVERSITY OF TSUKUBA, INSTITUTE OF APPLIED PHYSICS, PROFESSOR, 物理工学系, 教授 (90251040)
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| Project Period (FY) |
2001 – 2002
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| Keywords | POSITRON ANNIHILATION / MONOENERGETIC POSITRON BEAM / GaN / POINT DEFECT / IMPURITY DOPING / REAR EARTH / ZnO |
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| Research Abstract |
Positron annihilation is an established technique to investigate point defects in materials. We probed defects in Eu-and Tb-doped GaN films grown on sapphire substrates by gas-source molecular beam epitaxy with a monoenergetic positron beam. In both Eu- and Tb-doped samples, we observed vacancy clusters consisting of two or more vacancies. These defects were introduced by replacing Ga with rare-earth elements, and resulting in distortion of the host matrix. We studied the correlation between luminescence originating from the intra-4f-transitions of Eu^<3+> and the crystal quality of GaN film. In film doped at 2-at.% Eu, the mean open volume of the vacancies near the interface between the GaN film and the sapphire substrate was found to be larger than that in the subsurface region. The increase in the open volume of the defects correlated with the lowering coordination symmetry of Eu^<3+> and the increase in the transition rate of its 4f-electrons.
Zinc oxide (ZnO) thin films grown on ScAlMgO_4 substrates were also studied. We measured Doppler broadening spectra of annihilation radiation and photoluminescence spectra for the ZnO films deposited by laser molecular-beam epitaxy and single crystal ZnO. Although the lifetime of positrons in single crystal ZnO was close to the lifetime of positrons annihilated from the free state, the diffusion length of positrons was shorter than that for typical defect-free materials. We attribute this to the scattering of positrons by native defects. For the ZnO films, we observed a correlation between the defects and the lifetime of bound exciton emissions τ_<Ex> ; the main defect species detected by positron annihilation was Zn vacancies or other related defects. Isochronal annealing at 750-850℃ was found to introduce additional vacancy-type defects into the film, although the value of τ_<Ex> was scarcely changed by the annealing.
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