Structure and Morphology Characters of GaN Grown by ECR-MBE Using Hydrogen-Nitrogen Mixed Gas Plasma
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Tsutomu Araki, Yasuo Chiba and Yasushi Nanishi Department of Photonics, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu 525-8577, Japan. ABSTRACT GaN growth by electron-cyclotron-resonance plasma-excited molecular beam epitaxy using hydrogen-nitrogen mixed gas plasma were carried out on GaN templates with a different polar-surface. Structure and surface morphology of the GaN layers were characterized using transmission electron microscopy. The GaN layer grown with hydrogen on N-polar template showed a relatively flat morphology including hillocks. Columnar domain existed in the center of the hillock, which might be attributed to the existence of tiny inversion domain with Ga-polarity. On the other hand, columnar structure was formed in the GaN layer grown with hydrogen on Ga-polar template.
INTROCUCTION GaN and related III-V nitrides are promising semiconductors which can have applications in both optical devices including light emitting diodes in the blue-green and ultraviolet wavelength region, and electronic devices operating at high temperature, high frequency and high power. The recent commercial realization of light emitting diodes and the achievement of semiconductor lasers in the III-V nitrides have promoted much more attention in the field of research. These advances have been primarily achieved using metalorganic chemical vapor deposition (MOCVD) for the crystal growth. Molecular beam epitaxy (MBE) has been considered a suitable technique for the fabrication of highquality device structure using III-V nitrides due to the high controllability of atomic order thickness, interface abruptness, composition and so on. One of the key issues plaguing the MBE growth of III-V nitrides has been a relatively low growth rate compared to other common growth techniques. Recently, high growth rates of GaN have been achieved by the development of nitrogen plasma sources. Fujita et al reported a growth rate of 1.4 µm/h in GaN growth using RF nitrogen plasma source [1]. Another approaches to achieve GaN growth with high growth rates is using an ammonia as the nitrogen source. Yang et al. [2] and Grandjean et al. [3] achieved growth rates of 1 µm/h and 1.2 µm/h respectively by MBE using the ammonia source. On the other hand, Zhonghai Yu et al. reported an increase in GaN growth rate by as much as a factor of 2 by the addition of atomic hydrogen during MBE growth [4]. We have also demonstrated the increase in the growth rate using hydrogen and nitrogen mixed gas plasma for electron-cyclotronresonance (ECR) plasma-excited MBE [5]. In previous works [6,7], structural changes in GaN grown with hydrogen were investigated using electron microscopy, in which the dispersed columnar structure with a hexagonal pyramid surface was observed. The formation mechanism of the columnar structure was discussed by assuming nonuniformity of polarity of GaN surface. In this work, to develop a deeper
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understanding of the growth process of MBE-grown GaN with hydrogen, GaN growth by ECR-MBE using hydrogen and nitrogen mixed gas pla
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