AlN nanowires with a diameter of 20 nm were grown stochastically by the vapour-liquid-solid (VLS) method. At low temperatures below 1000 °C the Kirkendall effect during the alloying of aluminium and the catalyst resulted in the formation of three-dimensional nanostructures like lamellas and nano flowers. The high temperatures above 1000 °C, which are necessary to grow the nanowires complicate the control of their formation. Small catalyst droplets of 20 nm diameter are not stable due to their evaporation. Thus, in contrast to the classical approach to grow a single nano wire out of one droplet, we grew dense networks of nanowires inside larger 3D structures with diameters up to 5 µm. Depending on the growth temperature and the droplet geometry the nanowires inside of these networks are connected by angles of 90° ("cubic") or 120° ("hexagonal").

In this work we investigated the influence of the AlN material quality on the etching rate in KOH-based solutions. Thus, AlN layers were deposited by three different methods on sapphire and silicon substrates (i) by metal organic chemical vapor deposition (MOCVD), (ii) by molecular beam epitaxy (MBE), and (iii) by reactive sputter deposition. The etch rate is strongly dependent on crystal quality and etch temperatures. The high quality MBE-AlN could be etch anisotropic with a preferred lateral component in [ ]1120 direction at 60 °C while the polycrystalline AlN layers we etched isotropic and homogenously already at room temperature. The wet chemical etching in KOH solution is mainly an etching along defects and grain boundaries.

The growth of Si-doped AlN(0001) thin films on Al2O3(0001) substrates by plasma-induced molecular-beam epitaxy is reported. We have found that Si positively affects the epitaxy being an effective surfactant for AlN growth with a remarkable impact on the crystal quality. It was proven that the characteristic surface reconstruction sequences frequently related to the Al adatoms are obviously Si induced on AlN(0001) surfaces. It was also observed that heavy doping conditions result in volume segregation of Si on the threading dislocation network and in the formation of an amorphous (AlO)(SiO)N cap layer caused by surface oxidation of the accumulated Al and segregated Si. The electron affinity was measured to be smaller than 0.5eV on the clean AlN surface after removing of the cap layer using Ar+ sputtering.

In this work, coalescence aspects of wurtzite-III-nitride epitaxy are addressed. The coalescence phenomena have been studied in thin epilayers by means of electron and atomic force microscopies, and electron and x-ray diffractions. This study generalizes the growth parameters responsible for the rapid coalescence of III-nitride films, and describes the coalescence qualitatively and, partly, analytically for the case of heteroepitaxy in nonequilibrium conditions. Coalescence time and the corresponding diffusion coefficients at elevated temperatures were estimated for GaN and InN depositions. The rate of coalescence has been found to impact on the structure and morphology of III-nitride epilayers. A simple growth model was suggested to explain the formation of domain boundaries and ͑0001͒ stacking faults formed during the coalescence. In particular, it is shown that two adjacent and tilted, hexagonal-shaped 2H domains may form a noncoherent boundary explicitly along a ͕11 ¯00͖ plane. We also suggest that the interaction between tilted domains induces the localized lateral growth of the most epitaxially oriented domain forming a basal ͑0001͒ stacking fault followed by the formation of surface macrosteps, and consequently the termination of a threading dislocation by its dissociation and propagation under the formed ͑0001͒ stacking fault.

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