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Abstractauthoren We propose partially relaxed ultrathin GaN interlayer for strain control of AlN on SiC substrates. According to the degree of relaxation of the GaN interlayer, the lattice constant of the interlayer changes from that of SiC to that of bulk GaN, which leads to strain control of an AlN top layer grown on the interlayer. Growth of these layers is conducted by plasma-assisted molecular beam epitaxy. Before growing the interlayer, an AlN layer coherently grown on SiC is used as a template layer. The interlayers that have different degrees of relaxation are successfully obtained by changing the interlayer thickness. As a result, strain values of the AlN top layer grown on the interlayers are widely controlled from compressive (−0.53%) to tensile (+ 0.07%). TEM observation revealed the relaxation is induced by U-shaped half-loop dislocations originating from the GaN interlayer. [ABSTRACT FROM AUTHOR]

We present a detailed atomistic analysis of the electronic properties of m-plane InGaN/GaN quantum wells. The tight-binding model used treats realistically sized systems atomistically and accounts for compositional and structural inhomogeneities. Local variation in strain and built-in potential arising from random alloy fluctuations are explicitly included in the model. Many energy states of the supercells considered are calculated in order to determine the impact of the alloy fluctuations on the electronic structure of the system under investigation. We find that while the electrons are relatively insensitive to the local indium environment, the hole states are highly sensitive to it and are subject to very strong localization effects. These effects persist several states into the valence band. This strong localization of the hole states leads to a very broad distribution of ground state energies in different random configurations. Furthermore, we see that the localization leads to poor overlap between different hole states resulting in a reduced probability of transfer of carriers between different states. This feature should play an important role for transport properties in m-plane InGaN/GaN QWs. [ABSTRACT FROM AUTHOR]

The thermal expansion coefficient mismatch between GaN and SiC is lower than between GaN and Si. However it is usually observed that GaN on SiC/Si templates has higher tensile stress than GaN directly on Si. To provide an insight into the relationship between SiC template residual stress and GaN overlayer residual stress and crystal quality, we have analyzed the in-plane residual stress gradient present in GaN/SiC microstructure arrays of various dimensions and shapes using micro-Raman spectroscopy. It was found that the GaN overlayer residual stress is directly proportional to the SiC buffer layer residual stress. GaN films with lower residual stress also resulted in GaN films with improved crystal quality. Our study shows that the frequently encountered problems of high tensile stress in GaN films deposited on SiC templates is due to the high tensile residual stress in the SiC layers. The poorer GaN crystal quality deposited on SiC templates reported in literature is also likely due to the high tensile stress in the SiC templates. In order to grow GaN films with sufficient compressive stress and crystal quality for subsequent device processing, it is crucial to reduce the high tensile stress present in the SiC templates. [ABSTRACT FROM AUTHOR]

GaN layers have been grown on double-side-polished sapphire substrates using hydride vapor phase epitaxy. The GaN layers on each side of the substrate were alternately grown using a new susceptor with a rotating mechanism. Although a conventional GaN layer grown on one side of a sapphire substrate exhibits a small radius of curvature, the alternately double-sided-grown GaN template exhibits a large radius of curvature. The radius of curvature of the alternately double-sided-grown GaN template with a thickness of 180 μm was found to be approximately 16.4 m, and was larger than the 0.5 m radius of curvature of the conventional GaN template. [ABSTRACT FROM AUTHOR]

A new approach is proposed to the synthesis of a semipolar GaN on a Si(100) substrate at the surface of which the V‐shaped nanostructures with the characteristic size of elements as low as 100 nm are formed. It has been demonstrated that application of buffer layers of 3C‐SiC and AlN enables formation of the GaN(10–11) layer characterized by the full width at half maximum value as low as ωθ ≈45 arcmin for the X‐ray diffraction rocking curve. The model based on anisotropic nucleation of AlN on the V‐shaped nanostructure is proposed to explain the growth of the GaN layer in a single semipolar direction. In this article, Bessolov et al. focus on the growth of the GaN layer in a semipolar direction by heteroepitaxy of the GaN layer on nano‐patterned Si(100) substrate with V‐shaped nano‐grooves arranged with the period as low as 100 nm, combined with the synthesis of a nano‐sized SiC layer formed by solid‐phase substitution of silicon atoms by carbon atoms. [ABSTRACT FROM AUTHOR]

InGaN alloys have been attracting tremendous interest because of the large range of wavelengths covered when tuning the In to Ga ratio, offering extensive band gap engineering possibilities as well as the opportunity to achieve longer wavelength optoelectronic devices. Industrialization of InGaN materials with large In contents is however still limited by challenges imposed by intrinsic material properties. At typical InGaN growth temperatures the In desorption rate is lower than the In–N bond decomposition rate, making it difficult to avoid accumulation of metal In droplets on the surface. Hestroffer et al. (pp. 626–629) have established a growth diagram for InGaN grown on (0001) GaN at a constant temperature of 575 °C versus Ga and In fluxes. The authors identify different regimes, namely: N‐rich, intermediate In‐rich, droplet‐accumulation In‐rich, and Ga‐rich. Compositionally graded InGaN layers are grown by ramping the In and Ga fluxes in parallel under two distinct growth regimes. Structural and optical properties of the two types of grades are compared. The growth diagram proves to be a useful tool in controlling the metal fluxes and thereby the stoichiometry conditions on the surface during the growth of compositionally graded layers. [ABSTRACT FROM AUTHOR]