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STUDY OF POINT DEFECTS IN GaN AND RELATED COMPOUND SEMICONDUCTORS BY MEANS OF POSITRON ANNIHILATION

正电子湮灭法研究GaN及相关化合物半导体中的点缺陷

基本信息

批准号：
13650332
负责人：
UEDONO Akira
金额：
$ 1.34万
依托单位：
UNIVERSITY OF TSUKUBA
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650332/
关键词：
POSITRON ANNIHILATION MONOENERGETIC POSITRON BEAM GaN POINT DEFECT IMPURITY DOPING REAR EARTH ZnO Tb Eu

项目摘要

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.

正电子湮没是研究材料中点缺陷的一种成熟技术。我们用单能正电子束探测了在蓝宝石衬底上用气体源分子束外延生长的掺Eu和Tb的GaN薄膜中的缺陷。在Eu和Tb掺杂的样品中，我们观察到由两个或多个空位组成的空位簇。这些缺陷是通过用稀土元素取代Ga而引入的，并导致基质的畸变。我们研究了Eu^<3+>的4f内跃迁发光与GaN薄膜晶体质量之间的关系。In膜掺杂2原子% Eu，发现GaN薄膜与蓝宝石衬底界面附近的空位平均开放体积大于亚表面区域的空位平均开放体积。缺陷的开放体积的增加与Eu^<3+>的配位对称性降低和4f电子跃迁速率的增加有关。测量了激光分子束外延生长的ZnO薄膜和单晶ZnO的湮没辐射多普勒展宽谱和光致发光谱。虽然单晶ZnO中正电子的寿命接近于从自由态湮灭的正电子的寿命，但正电子的扩散长度比典型的无缺陷材料短。我们把这归因于正电子被自然缺陷散射。对于ZnO薄膜，我们观察到了缺陷与束缚激子发射寿命τ之间的相关性<Ex>，正电子湮没检测到的主要缺陷种类是Zn空位或其他相关缺陷。在750-850℃的等时退火，虽然τ_（max）值几乎没有变化，但在薄膜中引入了额外的空位型缺陷<Ex>。