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With this work we investigate several different ways to create marker layers for the ex situ characterisation of hydride vapour phase epitaxial (HVPE) gallium nitride (GaN) growth. Significant variations of the charge carrier concentration of GaN crystals become visible as marker lines in cross section investigations using optical microscopy and secondary electron microscopy (SEM). Pulsed intentional silicon and germanium doping leads to a good brightness contrast in cross section SEM micrographs and optical microscopy images. They appear as a black contrast in SEM. Pulsed manganese doping results in bright contrast marker layers in SEM, which is a result of the variation of the charge carrier concentration in the opposite direction, with respect to the background impurity level of the material. Marker layers are employed to determine the temperature transition point between 3D- and step flow GaN growth mode for the used set of growth parameters. A trend for the development of the growth rate of the c-facet as a function of the temperature is observed. [ABSTRACT FROM AUTHOR]

Abstract: In this research, hexagonal wurtzite structure gallium nitride (GaN) thin film was grown on silicon (Si) substrate by using spin coating deposition method. Simple ethanol-based precursor with the addition of diethanolamine solution was used. High resolution X-ray diffraction results revealed that wurtzite structure GaN thin film with (002) preferred orientation was deposited on Si substrate. Flied-emission scanning electron microscopy and atomic force microscopy results showed that crack free GaN thin film with uniform and dense grains of GaN was formed. Finally, lattice vibrational characterization by p-polarized infrared reflectance technique revealed a strong reststrahlen feature of crystalline wurtzite GaN, and the transverse and longitudinal phonon modes of wurtzite GaN were clearly identified. [Copyright &y& Elsevier]

Abstract: Two kinds of novel GaN nanotowers on silicon (111) substrates by employing ultrathin Ni catalyst films (0.2nm) were successfully synthesized at different growth temperatures using a metal–organic chemical vapor deposition system. Scanning electron microscopy indicated that the density and growth direction of the nanotowers were highly sensitive to changes of growth temperature. The morphologies were characterized in detail, and showed triangular and hexagonal nanotowers which were oriented predominantly along and [0001] directions, respectively. Finally, a new growth mechanism is stated to explain the growth of these two novel GaN nanotowers. [Copyright &y& Elsevier]

Abstract: GaN synthesized by close space vapor transport in vacuum using GaN powder as the source material is reported. According to X-ray diffraction measurements, samples grown onto sapphire substrates are polycrystalline with the wurzite structure, while those grown onto fused silica substrates are amorphous. Scanning electron microscope and energy dispersive spectroscopy results show that the surface of the samples is composed of rounded droplets of GaN. Room temperature photoluminescence shows near band-edge emission and a broad defect band. Possible mechanisms allowing the deposition of GaN from the vapors of GaN powder are discussed. [Copyright &y& Elsevier]

Abstract: The synthesis of GaN by selective area growth using Hydride Vapor Phase Epitaxy (SAG-HVPE) is reported for stripes patterned along and GaN on c-plane sapphire substrates. A systematic control of the GaN morphologies was carried out by both cross-sectional and surface Scanning Electron Microscopy (SEM). A complete HVPE cartography of GaN-SAG revealed domains of zero growth rates at high concentration of hydrogen in the carrier gas. The determination of the mechanisms that govern the growth of GaN morphologies was particularly emphasized. A theoretical model based on thermodynamic and kinetic analyses of the grown (0001) GaN layers was discussed, in combination with experiments on unmasked (0001) GaN and patterned GaN/c-plane sapphire substrates. Long HVPE runs were performed to demonstrate that the prevailing growth mechanism, for high hydrogen concentration in the carrier gas, is a mechanism based on a dechlorination by GaCl2 gas species. This mechanism leads to growth blockade of GaN growth and constitutes a very interesting issue for shaping GaN material as an alternative to top-down micro- and nano-technologies. [Copyright &y& Elsevier]

We report nano-selective area growth (NSAG) of BGaN by MOCVD on AlN/Si(111) and GaN templates resulting in 150 nm single crystalline nanopyramids. This is in contrast to unmasked or micro-selective area growth, which results in a multi-crystalline structure on both substrates. Various characterization techniques were used to evaluate NSAG as a viable technique to improve BGaN material quality on AlN/Si(111) using results of GaN NSAG and unmasked BGaN growth for comparison. Evaluation of BGaN nanopyramid quality, shape and size uniformity revealed that the growth mechanism is the same on both the templates. Further STEM analysis of BGaN nanopyramids on AlN/Si (111) templates confirmed that these are single-crystalline structures without any dislocations, likely due to single nucleation occurring in the 80 nm mask opening. CL results correspond to boron content between 1.7% and 2.0% in the nanopyramids. We conclude that NSAG is promising for growth of high-quality BGaN nanostructures and complex nano-heterostructures, especially for low-cost silicon substrates. [ABSTRACT FROM AUTHOR]