Reciprocal Space Mapping of X-Ray Diffraction Intensity of GaN-Based Laser Diodes Grown on GaN Substrates
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Y5.40.1
Reciprocal Space Mapping of X-Ray Diffraction Intensity of GaN-Based Laser Diodes Grown on GaN Substrates K. Tachibana, Y. Harada, S. Saito, S. Nunoue, H. Katsuno, C. Hongo, G. Hatakoshi1, and M. Onomura Corporate Research and Development Center, Toshiba Corporation 1 Toshiba Research Consulting Corporation 1, Komukai-Toshiba-cho, Saiwai-ku, Kawasaki 212-8582, Japan
ABSTRACT Characterization by reciprocal space mapping of x-ray diffraction (XRD) intensity was carried out for epitaxial layers of GaN-based laser structures on two GaN substrates: GaN substrate and GaN template on sapphire substrate. The difference between these two substrates was shown clearly. The distribution of XRD intensity of the epitaxial layers on GaN substrate was smaller than that of the epitaxial layers on GaN template on sapphire substrate. In the lasers with the epitaxial structure on GaN substrate, the light output power was as high as 200 mW under continuous-wave operation at room temperature. Excellent noise characteristics with relative intensity noise of -132 dB/Hz were also obtained at a low light output power of 3 mW without any high-frequency modulation. These results support that GaN substrates are promising for realizing GaN-based lasers with high performance.
INTRODUCTION Blue-violet semiconductor lasers have been expected intensively for light sources of next-generation optical disc systems. A laser with a high light output power of more than 30 mW under continuous-wave (cw) operation has been demonstrated [1]. Lasers with higher light output power are strongly desired for high-speed recording in optical disc systems. In the GaN-based lasers, substrates have significant effect on the device characteristics. Recently, large-scale GaN substrates were developed [2] and further development has been conducted. GaN substrates enable the homoepitaxy of III-nitrides and thus the lasers on GaN substrates are expected to have superior characteristics such as higher light output power and higher reliability. However, the epitaxial layers on GaN substrates have not been investigated in detail yet. In this paper, reciprocal space maps (RSMs) of x-ray diffraction (XRD) intensity of the epitaxial layers of GaN-based laser structures on GaN substrate have been investigated, and device characteristics of lasers with the epitaxial structure on GaN substrate have been estimated. The distribution width of XRD intensity profile of the epitaxial layers on GaN substrate was smaller than that of the epitaxial layers on GaN template on sapphire substrate. In the lasers on GaN substrate, the light output power was as high as 200 mW under cw operation at room temperature. Excellent noise characteristics with relative intensity noise (RIN) of -132 dB/Hz at a light output power of 3 mW were obtained.
Y5.40.2
RECIPROCAL SPACE MAPPING of X-RAY DIFFRACTION INTENSITY Two substrates were used for the epitaxial growth by metalorganic chemical vapor deposition. One was n-GaN substrate (by Sumitomo Electric Industries, Ltd.). The other was GaN templat
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