A high quality AlGaN layer with low dislocation density and low c-axis tilt angle in wing regions was demonstrated by the advanced ELO technique, namely air-bridged lateral epitaxial growth. An underlying GaN seed layer was grooved along the 〈1100〉 GaN direction to the sapphire substrate, whose sidewalls and etched bottoms were covered with silicon nitride masks, and regrowth of AlGaN was carried out by a low-pressure metalorganic vapor phase epitaxy system. Fabrication of air-bridged structures suppresses interference of nucleated poly-crystals on the silicon nitride masks during lateral growth, and the low dislocation density AlGaN layer was realized. The threading dislocation density in the wing regions was reduced to 2 × 10 7 cm -2 and the c-axis tilt angle was 0.19°.1 Introduction III -V nitrides have shown potential for use in shorter wavelength optical devices. These nitride devices are usually fabricated on sapphire substrates because of a lack of large-size GaN substrates. The threading dislocation (TD) density has been known between 10 8 cm -2 and 10 10 cm -2 due to the large lattice mismatch between GaN and sapphire. In order to reduce the TD density, epitaxial lateral overgrowth (ELO) techniques have been performed [1,2]. The ELO techniques have achieved to considerable success in reducing the TD density to 10 6 cm -2 range in wing regions. A c-axis tilting in the wing regions, however, was observed with a different direction on both sides of seed regions in an azimuth perpendicular to the stripe direction. The tilt angle of the wing regions is commonly 0.2°-1.0° for a thin GaN layer by using (0002) X-ray diffraction (XRD) rocking curve measurements [3,4]. In our previous work, we have reported an advanced ELO technique, namely "air-bridged lateral epitaxial growth (ABLEG)" [5,6]. By using the ABLEG technique, the TD density at the surface of the wing regions is reduced to less than 5 × 10 6 cm -2 and the tilt angle of the wing regions is lowered to be 0.1°. In conventional nitride based device structures, AlGaN layers are grown on underlying GaN layers. It is necessary that high power and low noise optical devices have crack-free and thick AlGaN cladding layers. It is not, however, easy to grow high-crystalline quality AlGaN/GaN heterostructures due to the lattice mismatch. In order to suppress the crack formation, growth of an AlGaN layer on an underlying AlGaN layer instead of the underlying GaN layer is effective, because the lattice mismatch is relatively small. But it is quite difficult to grow a low TD density AlGaN layer on sapphire substrate, and to reduce the TD density by ELO techniques because of nucleation of poly-crystals on the mask surface [7]. Several apporaches have reported a TD density reduction of AlGaN layer [8,9]. The ABLEG technique not only reduces the interfacial stress between the wing regions and the masks, but also suppresses interference of nucleated poly-crystals during the lateral growth. In this study, we have performed ABLEG of AlGaN and achieved a TD density reductio...
We have clarified the compositional dependence of the thermal stabilities and chemical structures of aluminum oxynitride (AlON) films. Thermally induced changes in composition and structure of AlON with various compositional ratio (R=N/(N+O)) have been investigated. Although AlON films show amorphous phase in the wide range of R, we find that AlON has two chemically different phases with different thermal stability, which are separated at critical nitrogen composition of R=0.4. Rutherford back scattering measurement and infrared spectroscopy indicate that AlON with R<0.4 shows structural phase transition and nitrogen desorption occurred by thermal annealing. In contrast, AlON with R>0.4 is thermally stable amorphous phase. We propose a model of bonding structure which explains the thermal stability of AlON.
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