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We present a detailed study of the structural characteristics of molecular beam epitaxy grown nonpolar InN films with a- and m-plane surface orientations on r-plane sapphire and (100) γ-LiAlO2, respectively, and semipolar (1011) InN grown on r-plane sapphire. The on-axis rocking curve (RC) widths were found to exhibit anisotropic dependence on the azimuth angle with minima at InN [0001] for the a-plane films, and maxima at InN [0001] for the m-plane and semipolar films. The different contributions to the RC broadening are analyzed and discussed. The finite size of the crystallites and extended defects are suggested to be the dominant factors determining the RC anisotropy in a-plane InN, while surface roughness and curvature could not play a major role. Furthermore, strategy to reduce the anisotropy and magnitude of the tilt and minimize defect densities in a-plane InN films is suggested. In contrast to the nonpolar films, the semipolar InN was found to contain two domains nucleating on zinc-blende InN(111)A and InN(111)B faces. These two wurtzite domains develop with different growth rates, which was suggested to be a consequence of their different polarity. Both, a- and m-plane InN films have basal stacking fault densities similar or even lower compared to nonpolar InN grown on free-standing GaN substrates, indicating good prospects of heteroepitaxy on foreign substrates for the growth of InN-based devices. [ABSTRACT FROM AUTHOR]

We report on a growth by molecular beam epitaxy of InN:In semiconductor/metal composite structures containing periodically inserted arrays of In clusters formed by intentional deposition of In metal films in a thickness range of 2–48 monolayers. It was found that indium insertions do not change markedly carrier mobility in the composites, that remains in the 1300–1600 cm2/(V s) range, while carrier concentration increases with rising In amount. Spectra of thermally detected optical absorption do not exhibit a noticeable Burstein-Moss shift of a principal absorption edge with increasing the carrier concentration, but rather complicated modification of their shapes. [ABSTRACT FROM AUTHOR]

InN nanocolumns (NCs) without vertical diameter variation have been grown on GaN templates by molecular beam epitaxy. Growth temperature is the key parameter to obtain such shaped InN NCs. The density and surface distribution can be controlled by the V / III ratio and initial nucleation process. Intense photoluminescence (PL) is observed for the optimal InN NCs, about two orders of magnitude stronger than the InN epilayers. Superior excitation power and temperature dependence of the PL indicate significantly reduced defect density and residual electron density, non-degenerate property, and possibly suggest that there is a small or negligible level of electron accumulation at the smooth non-polar lateral surfaces. [ABSTRACT FROM AUTHOR]

Abstract: InN nanocolumns were grown on (0001) sapphire substrates by radio-frequency plasma-assisted molecular-beam epitaxy, simply with substrate nitridation, InN nucleation, and high V/III growth conditions. Here, the InN nucleation was conducted by forming In droplets on the nitridated substrates and subsequently nitriding these In droplets. We investigated the growth evolution of InN nanocolumns and the growth-temperature dependence of the morphology. X-ray rocking curves (XRC) for the (0002) reflection of the samples basically consisted of two components: a broad peak and a very sharp one. We propose that the broad peak came from the lower part of relatively short nanocolumns and the near-interface region of relatively long nanocolumns. In contrast, the sharp peak came from the (strain-free) upper part of relatively short nanocolumns and the high-crystal-quality region apart from the interface in relatively long InN nanocolumns. The relative intensity of the latter to the former increased with growth time. The shape of the nanocolumns varied with growth temperature: nanocolumns grown at 380 and 420°C had a taper-like appearance, but the top broadened with increasing growth temperature, becoming broader at the top than the base at 470 and 500°C. When we grew InN nanocolumns under the same conditions, but without surface nitridation, the subsequent columns were not all along a c-axis. If In droplets were not used, then columns did not form. Thus, both the surface nitridation and In droplets were needed to form -axis aligned nanocolumns. [Copyright &y& Elsevier]

GaN films were grown at various V/III ratios on sapphire (0 0 0 1) substrates with and without nitridation process by radio-frequency plasma-excited molecular beam epitaxy. Based on the results of X-ray diffraction pole-figure and φ scan measurements, the GaN film grown without nitridation process has a tendency to form the metastable in-plane rotation domain by ∼11° from the substrate, in addition to the main domain rotated by 30° from the substrate. In suppressing the formation of the metastable in-plane rotation domain, it is found to be very effective to perform the nitridation process. In addition, even in GaN films grown without nitridation process, decrease in V/III ratio enables us to suppress the formation of the metastable domain. The rotation domains are considered to have the epitaxial relationship of [1 2 &3macr; 0]GaN||[1 1 &2macr; 0]sapphire and [&1macr; &2macr; 3 0]GaN||[1 1 &2macr; 0]sapphire. [Copyright &y& Elsevier]

Abstract: The structural and electrical properties of N- and In-polar InN films grown directly on substrates were investigated. The twist contribution of directly grown InN films, which was defined by the estimated X-ray rocking curve''s full-width at half-maximum (XRC''s FWHM) of InN (101¯0) reflection, varied considerably by at least 40arcmin for both N- and In-polar InN films, depending on growth conditions. In contrast, the tilt contribution, defined by the XRC''s FWHM of InN (0002) reflection, was roughly fixed at 1.5–2.5arcmin for N-polar InN films and 8–12arcmin for In-polar InN films. For samples with the same twist contribution, In-polar InN films had larger tilt contribution than N-polar InN films. Nevertheless, electrical properties of In-polar InN had much better properties than those of N-polar InN films. [Copyright &y& Elsevier]

Abstract: For the growth of further-improved InN film on a sapphire substrate, the effects of the conventional initial growth process, which is substrate nitridation and the deposition of a low-temperature InN buffer layer prior to growth, were carefully reinvestigated. Although the deposition of the low-temperature InN buffer layer realized a flat surface, the degradation of the crystallinity simultaneously resulted. The insertion of a high-temperature InN buffer layer solved this problem, and a high-quality InN film with a small tilt-distribution and a very flat surface was realized. [Copyright &y& Elsevier]

Abstract: High-quality epitaxial InN films have been employed as underlying templates for the growth of In-rich In x Ga1− x N (0.71⩽x⩽0.90) films by radio-frequency plasma assisted molecular beam epitaxy. The epitaxial InN films (InN templates) with the thickness of 500nm were grown on (0001) sapphire substrates with a low-temperature deposited 10nm thick InN (LT-InN) buffer layer, and then In-rich In x Ga1− x N films with the thickness of 250nm were grown on these InN templates. As compared with In-rich In x Ga1− x N films grown directly on the LT-InN buffer layers, the In-rich In x Ga1− x N films grown on the InN templates showed a decrease in full-width at half-maximum of the (0002) X-ray rocking curves. It was found that the insertion of the InN template was very effective in improving the crystalline quality of In-rich In x Ga1− x N. Optical properties were also investigated by photoluminescence. Lattice distortion of the In-rich In x Ga1− x N films induced by the underlying InN templates is also discussed. [Copyright &y& Elsevier]