Beam Induced Lateral Epitaxy: A New Way to Lateral Growth in Molecular Beam Epitaxy
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BEAM INDUCED LATERAL EPITAXY: A NEW WAY TO LATERAL GROWTH IN MOLECULAR BEAM EPITAXY Shigeya Naritsuka1),2), Koji Saitoh1), Takashi Suzuki1) and Takahiro Maruyama1),2) 1) Meijo University, Dept. of Materials Science and Engineering, Nagoya, 468-8502 Japan 2) Meijo University, 21st century COE program “NANO FACTORY” We developed a new technique of epitaxial lateral growth without using oxide masks called beam induced lateral epitaxy (BILE). In this technique, molecular beams are directed at a nearly glancing angle with respect to a substrate that has pre-fabricated truncated ridges. By using BILE we grew GaAs laterally from the side of ridges on a GaAs substrate. The growth behavior of BILE strongly depended on both incident angle of the Ga beam and the crystal orientation of the truncated ridges. The formation of facets on the lateral growth front controlled the grown shape of the layers. By using a (111) B substrate with BILE, we grew a smooth, flat (111) B facet on the top of the layer. Introduction In a highly mismatched heteroepitaxial system, a large lattice mismatch and a big difference in thermal expansion coefficients between the epitaxial layer and the substrate produces lattice strain that leads to dislocation densities exceeding 106 cm-2 and poor device characteristics [1-3]. For example, such strain continuously generates dark-line defect (DLD) networks during the operation of laser diodes, which act as centers for nonradiative recombination and are responsible for rapid degradation of the diode [4-5]. The strain should be effectively repressed in heteroepitaxy and the crystallinity of the heteroepitaxial layers should be improved for the fabrication of devices with superior characteristics and long lifetimes. Although epitaxial lateral overgrowth can be used to overcome these difficulties [6-10], it is much convenient if the growth can be performed in molecular beam epitaxy (MBE) instead of liquid phase epitaxy (LPE). To address this problem, we recently proposed a new technique called beam induced lateral epitaxy (BILE) for lateral overgrowth in MBE [12]. In BILE, lateral overgrowth occurs by directing the molecular beam at a low angle to a substrate that has truncated ridges. Selective growth can be achieved under a relatively low growth temperature without a SiO2 mask. The method is good at preserving the surface smoothness due to the low amount of evaporation of the component at low temperature. But until now, BILE on GaAs (001) resulted in a rough upper surface that sometimes contained large steps [12]. To overcome these problems and to obtain a large, flat top surface, it is necessary to understand the mechanism of BILE in more detail. In this paper, we describe our study of BILE on GaAs in which we varied the Ga beam
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incidence angle, the crystal orientation of the ridges, and the substrate orientation. Through the use of scanning electron microscopy (SEM) images of the cross-section of these layers, the growth mechanism of BILE on GaAs substrate was thoroughly studied, particular
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