九州シンクロトロ ン光研究センター
県有ビームライン利用報告書
課 題 番 号 ： 2001133S

Ｂ Ｌ 番 号 ： BL15

（様式第 5 号）

X-ray diffraction topography on the homo -epitaxial GaN thin films
Kim Jaemyung, Okkyun Seo, Loku Singgappulige Rosantha Kumara,and Sakata Osami
National Institute for Materials Science
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１．概要（注：結論を含めて下さい）
We have performed x-ray diffraction topography imaging on the various fr ee-standing GaN
homo-epitaxial layers. X-rays of 1.284Å were selected by a double crystal monochromator.
The x-ray beam size was adjusted to be the maximum for the large area illumina tion. In thecase of m-plane GaN wafers, stripe patterns along the [0001] direction were observed. In orderto understand the origin of the stripe pattern, rocking curve imaging at (10-10), (12-30) and(22-41) planes were measured. For c-plane GaN, various crystal planes – (0002), (0004),(01-14), (01-15), (02-25), (02-26), (11-24), (12-35) – were selected by calculating diffraction
angles and inter-planar angles. Dislocation types were confirmed by comparing variousimages.

２．背景と目的A GaN one of the prominent materials for LED (light-emitting diode), high-power device, and high-frequency
devices has attracted its great attention. However, it was a big challenge to fabricate large-area GaN thin filmof high crystallinity. Especially high dislocation density was a big obstacle. In order to minimize thedislocation density, many fabrication methods were proposed for the crystal quality improvement, such as
HVPE (hydride vapor phase epitaxy). Although the crystal quality has been improved much, the crystal qualityof large-area is not so high and homogeneous enough to mass production. Therefore, it is imperative toevaluate the whole GaN wafer qualitatively and statistically.
３．実験内容（試料、実験方法、解析方法の説明）
The x-ray diffraction topography experiment was performed at BL15, SAGA, Japan. X-rays of 1.284Å wereselected by Si (111) double crystal monochromator (DCM). The x-ray bean size was adjusted to be about 5 cm
 1 cm. GaN wafers were placed in the rotation center of a goniometer. A flat panel detector of a pixel size of50  50 μm2 were placed at various Bragg angles. The diffraction images were automatically recorded with a0.001º step of the sample rotation angle. The schematic view of the experimental condition is sketched inFigure 1. The obtained images were stacked along the θ (sample rotation angle) direction and merged.
Maximum intensity, peak position, and FWHM (full width at half maximum) of each detector pixel werecalculated for the evaluation of the crystallinity. Similar measurements were performed on various Miller
indices such as (0002), (0004), (01-14), (01-15), (02-25), (02-26), (11-24), and (12-35) for understanding of
dislocation feature.

Figure 1. Schematic view of the experimental configuration. X-rays of 1.284Å were selected by Si (111)
double crystal monochromator. GaN wafers were put in the rotation center. A flat panel detector was placed
at Bragg angles, and diffraction images were recorded at various incident angles.
４．実験結果と考察
The merged x-ray diffraction topography images on c-plane GaN are illustrated in Figure 2. Maximum
intensity, peak position variation, and FWHM map shows texture structure in the GaN homo-epitaxial layer. In
the case of a (10-15) plane, the top and bottom of the image were deformed by x-ray beam size limitation. Thechange in images by g-vector indicates that the dislocation is dependent on the kinds of dislocation. We areanalyzing the relation between g-vector and dislocation.

Figure 2. Merged x-ray diffraction topography images of c-plane GaN under different g-vector. The
maximum intensity, peak position, and FWHM of each pixel are strongly dependent on the g-vector. The
unit in peak position image is degree.
５．今後の課題
It is necessary to analyze the topography image qualitatively and statistically for the GaN wafer quality

evaluation, such as dislocation density mapping.
６．参考文献1. J. Kim, O. Seo, S. Hiroi, Y. Irokawa, T. Nabatame, Y. Koide, and O. Sakata, Surface morphology
smoothing of a 2 inch-diameter GaN homoepitaxial layer observed by X-ray diffraction topography,
RSC Adv. 10, 1878-1882 (2020)
2. J. Kim, O. Seo, C. Song, S. Hiroi, Y. Chen, Y. Irokawa, T. Nabatame, Y. Koide, and O. Sakata,
Mapping of a Lattice-Plane Tilting in a GaN Wafer Using Energy-Resolved X-Ray Diffraction
Topography, Phys. Rev. Appl. 11, 024072 (2019)
3. J. Kim, O. Seo, C. Song, S. Hiroi, Y. Chen, Y. Irokawa, T. Nabatame, Y. Koide, and O. Sakata,
Lattice-plane bending angle modulation of Mg-doped GaN homoepitaxial layer observed by X-ray
diffraction topography, CrystEngComm 21, 2281-2285 (2019)
4. J. Kim, O. Seo, A. Tanaka, J. Chen, K. Watanabe, Y. Katsuya, T. Nabatame, Y. Irokawa, Y. Koide, O.
Sakata, Anisotropic mosaicity and lattice-plane twisting of an m-plane GaN homoepitaxial layer,
CrystEngComm 21, 4036-4041 (2019)
5. J. Kim, O. Seo, C. Song, Y. Chen, S. Hiroi, Y. Irokawa, T. Nabatame, Y. Koide, and O. Sakata,
Characterization of a 4-inch GaN wafer by X-ray diffraction topography, CrystEngComm 20,7761-7765 (2018)
6. J. Kim, O. Seo, C. Song, S. Hiroi, Y. Chen, Y. Irokawa, T. Nabatame, Y. Koide, O. Sakata,
Lattice-plane orientation mapping of homo-epitaxial GaN (0001) thin films via grazing-incidence
X-ray diffraction topography in 2-in. wafer, Appl. Phys. Express 11, 081002 (2018)
7. O. Seo, J. M. Kim, C. Song, Y. Loi, LSR. Kumara, S. Hiroi, Y. Chen, Y. Katsuya, Y. Irokawa, T.
Nabatame, Y. Koide, and O. Sakata, Evaluation of lattice curvature and crystalline homogeneity for
2-inch GaN homo-epitaxial layer, AIP Adv. 8, 075318 (2018)
７．論文発表・特許（注：本課題に関連するこれまでの代表的な成果）
1. J. Kim, O. Seo, S. Hiroi, Y. Irokawa, T. Nabatame, Y. Koide, and O. Sakata, Surface morphology
smoothing of a 2 inch-diameter GaN homoepitaxial layer observed by X-ray diffraction topography,
RSC Adv. 10, 1878-1882 (2020)
2. J. Kim, O. Seo, C. Song, S. Hiroi, Y. Chen, Y. Irokawa, T. Nabatame, Y. Koide, and O. Sakata,
Mapping of a Lattice-Plane Tilting in a GaN Wafer Using Energy-Resolved X-Ray Diffraction
Topography, Phys. Rev. Appl. 11, 024072 (2019)
3. J. Kim, O. Seo, C. Song, S. Hiroi, Y. Chen, Y. Irokawa, T. Nabatame, Y. Koide, and O. Sakata,
Lattice-plane bending angle modulation of Mg-doped GaN homoepitaxial layer observed by X-ray
diffraction topography, CrystEngComm 21, 2281-2285 (2019)
4. J. Kim, O. Seo, A. Tanaka, J. Chen, K. Watanabe, Y. Katsuya, T. Nabatame, Y. Irokawa, Y. Koide, O.
Sakata, Anisotropic mosaicity and lattice-plane twisting of an m-plane GaN homoepitaxial layer,
CrystEngComm 21, 4036-4041 (2019)
5. J. Kim, O. Seo, C. Song, Y. Chen, S. Hiroi, Y. Irokawa, T. Nabatame, Y. Koide, and O. Sakata,
Characterization of a 4-inch GaN wafer by X-ray diffraction topography, CrystEngComm 20,7761-7765 (2018)
6. J. Kim, O. Seo, C. Song, S. Hiroi, Y. Chen, Y. Irokawa, T. Nabatame, Y. Koide, O. Sakata,
Lattice-plane orientation mapping of homo-epitaxial GaN (0001) thin films via grazing-incidence
X-ray diffraction topography in 2-in. wafer, Appl. Phys. Express 11, 081002 (2018)
８．キーワード（注：試料及び実験方法を特定する用語を２～３）✓ X-ray diffraction topography, GaN, wide bandgap semiconductor
９．研究成果公開について（注：※２に記載した研究成果の公開について①と②のうち該当しない方を消してください。また、論文（査読付）発表と研究センターへの報告、または研究成果公報への原稿提出時期を記入してください（2018 年度実施課題は 2020 年度末が期限となります）。
長期タイプ課題は、ご利用の最終期の利用報告書にご記入ください。

① 論文（査読付）発表の報告② 研究成果公報の原稿提出（報告時期：予定 2021 年 3 月）
（提出時期：年月）