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In situ X-ray diffraction monitoring of GaInN growth by metalorganic vapor phase epitaxy

Motoaki Iwaya 1Taiji Yamamoto 1Daisuke Iida 1Mihoko Sowa 1Yasunari Kondo 1Tetsuya Takeuchi 1Satoshi Kamiyama 1Isamu Akasaki 1,2

1. Faculty of Science and Technology, Meijo University (MU), 1-501 Shiogamaguchi, Tempaku-ku, Nagoya, Nagoya 468-8502, Japan
2. Akasaki Research Center, Nagoya University, Nagoya 464-8601, Japan


GaInN-based high-brightness LED have been achieved as a result of several breakthroughs. To improve the performance of these devices, it is necessary to understand their crystal growth mechanism. For this purpose, the use of an in situ observation system during crystal growth is effective. XRD can be used to determine the lattice constant, composition, crystalline quality, and thickness. As such, an in situ XRD (I-XRD) monitoring system is expected to serve as a very helpful tool for observing epitaxial growth in real time. In this study, we developed a novel I-XRD system to observe the crystal growth of a nitride using a MOVPE reactor. We also present the results of real-time I-XRD monitoring. In general, a conventional XRD system requires a long measurement time because it is necessary to scan the X-ray source, detector, and/or substrate. In this light, it is desirable for the I-XRD system to perform the analysis quickly without the need for scanning during epitaxial growth. Toward this end, it is necessary to establish a high-time-resolution system for accurately analyzing the growth process. The proposed I-XRD measurement system is attached to an MOVPE reactor. The MOVPE reactor, in turn, is attached to the flange of a window consisting of Be. This I-XRD system does not require scanning. X-rays from the tube spread out as shown in the figure. The spread X-rays are focused using a Johansson curved crystal. The irradiation of the focused X-ray on the substrate can be controlled without scanning the angle. In addition, diffracted X-rays were detected using a one-dimensional CCD. These configurations can be measured in a manner equivalent to a (0002) 2θ/ω scan without the need for an analyzer crystal. In addition, this system can perform measurements within at most 1 s. In this system, the tilt component and distribution of lattice constant c can be simultaneously characterized from the FWHMs. We characterized a GaInN/GaN heterostructure and GaInN MQWs by using the proposed I-XRD system. We also measured these samples by ex situ XRD  through a 30-min-long process. An observation of the spectrum of the GaInN MQW measured at RT showed that although the proposed I-XRD system showed slightly lesser resolution compared to the conventional ex situ XRD system with an analyzer crystal, satellite peaks were confirmed between –2 and +2. As such, we consider that reasonably high resolution was achieved by the proposed system. Moreover, the I-XRD system revealed strain relaxation in GaInN films on GaN. The critical thickness of GaInN films could be estimated by the evolution of I-XRD with FWHMs as a function of GaInN thickness. The proposed I-XRD system enables measurements of the critical thicknesses that involve strain relaxation caused by the formation of surface pits with bent threading dislocations on GaInN during growth. This system is very useful for accurately evaluating the strain relaxation in the GaInN/GaN heterostructure during crystal growth.


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Related papers

Presentation: Oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 6, by Motoaki Iwaya
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-03-22 11:06
Revised:   2013-03-28 02:51