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Highlights • Ga-polar untwinned (1 0 −1 3) GaN was obtained by directional sputtering. • FWHM values are less than 550 aresec. • Al nucleation layer in directional sputtering affects the GaN layer much. Abstract Directional sputtering of Al and AlN on (1 0 −1 0) sapphire was used to obtain metal-polar (1 0 −1 3) templates. After overgrowth with AlN and GaN using metal-organic vapor phase epitaxy, we obtained untwinned (1 0 −1 3) GaN layers. Full width at half maximum of the X-ray rocking curve of symmetric (1 0 −1 3) GaN is less than 550 arcsec along both [3 0 −3 −2] GaN and [1 −2 1 0] GaN directions. Ga-polarity of the layers was confirmed by high-resolution scanning transmission electron microscopy. Careful optimization of time and temperature of the initial Al sputtered layer was a key parameter to achieve high quality GaN templates. [ABSTRACT FROM AUTHOR]

The effect of V/III ratio on the growth and properties of AlGaN layers grown on (112¯2) AlN templates grown on (101¯0) sapphire by metalorganic vapour phase epitaxy was studied. The surface morphology of the (112¯2) AlGaN layers and the (112¯2) AlN templates showed an undulation along [ 1 1 ¯ 00 ] AlGaN , AlN . The Al-content and thickness of the layers increased with decreasing V/III ratio due to a reduction in the parasitic reactions of the precursors. The Al-content of the (112¯2) layers was found to be in the range of 29.5−47.9%, which is lower than the composition of the simultaneously grown (0001) reference layers (30.4−58.0%). This was attributed to a higher density of cation (nitrogen) dangling bonds on the (112¯2) surface. Low temperature photoluminescence measurements of the (112¯2) layers showed an emission wavelength that shifts gradually from 273 nm to 306 nm with increasing V/III ratio. A decreased PL intensity of the layers with decreasing V/III ratio was attributed to an increase in cation vacancies. The Stokes-shift of the (112¯2) layers was estimated to be about 60−194 meV, and this shift increases with increasing Al-content (decreasing V/III ratio) correlated to an increased exciton localization. [ABSTRACT FROM AUTHOR]

We report on metalorganic vapor phase epitaxial growth of InAlN layers on (0001) and (11 [ABSTRACT FROM AUTHOR]

InGaN layers were grown simultaneously on polar (0001), and on semipolar (11 [ABSTRACT FROM AUTHOR]

Heteroepitaxial growth of AlN buffer layers directly on (101¯0) sapphire substrates by metalorganic vapour phase epitaxy has been investigated. A single-step growth procedure without a sapphire nitridation was employed resulting in mirror-like crack free ≈ 1.1 – 1.6 μ m thick AlN layers of single phase (112¯2) orientation. Trimethylaluminum pre-dose time and reactor pressure were optimized for surface roughness and crystal quality. The crystal quality was found to degrade with increasing pre-dose time and also reactor pressure. The smallest full width at half maximum value for on-axis X-ray rocking curve of the (112¯2) AlN layers was about 610 arcsec and 1480 arcsec along [1¯1¯23] AlN and [11¯00] AlN , respectively. The surface roughness, measured by atomic force microscopy using a 10 × 10 μ m 2 area, was in the range 2.6–3.5 nm. A basal stacking fault density of (7±1)×10 5 cm −1 was estimated by transmission electron microscopy. [ABSTRACT FROM AUTHOR]

We report on metal–organic vapor phase epitaxy (MOVPE) of (0001)InN layers simultaneously grown on a-plane (112¯0) and c-plane (0001) sapphire substrates. The substrates were nitridated at temperatures from 500°C to 1050°C prior to the growth of c-plane InN layers. Nitridation determined the polarity, the crystallinity, and the surface morphology of the InN layers. Nitridation temperatures above 800°C lead to N-polar InN layers, while nitridation temperatures from 700°C to 750°C produce mixed-polar InN layers, and nitridation temperatures from 500°C to 650°C produce In-polar InN layers. The roughness and crystallinity of the InN layers are correlated with the changes of polarity. The incorporation of nitrogen into the nitridation layers at different nitridation temperatures was measured. A strong N–Al bond signal after nitridation is correlated with N-polarity layers after overgrowth. [ABSTRACT FROM AUTHOR]

Abstract: Gallium nitride (GaN) nanowires, grown on gold-coated n-type Si(100) substrates, were synthesized using the vapor-phase epitaxy method. The grown GaN nanowires, with diameters in the range 20–60nm and lengths of several micrometers, were uniformly distributed on Si substrates. The GaN nanowires were grown via a vapor–liquid–solid mechanism. The characteristics of the grown GaN were investigated using X-ray diffraction, micro-Raman, and transmission electron microscopy, which found that the GaN nanowires on the Si(100) are of good crystalline quality. The electron field emission properties of the GaN nanowires (at room temperature) showed a low turn-on field of ∼3.96V/μm and a field enhancement factor of ∼1050. The sharp ends and rough surfaces of the GaN nanowires are responsible for their good field emission properties. [Copyright &y& Elsevier]