InGaN nanorods (NRs) for optoelectronic applications were grown on Si(111) by nitrogen radio-frequency plasma source molecular-beam epitaxy (rf-MBE). In order to detect their structural features, nanostructures were characterised by transmission electron microscopy (TEM) methods. Samples were prepared in cross-section orientation with the standard mechanical grinding process, followed by ion-thinning to electron transparency, without harvesting the NRs from the substrate.

Observations showed that the initial nanostructures starting from the GaN/Si interface were narrow NRs, having widths of the order of 10-30 nm, where two or three or more of them later merge to finally form NRs with widths in the range of 20-120 nm, the majority being at 50-70 nm. A few of the narrow NRs continued to grow higher than the merged ones and did not join together to form wider NRs, but they were actually linked to the wide NRs with low-angle grain boundaries. These NRs reached heights of nearly 1 µm, over twice the heights of merged NRs that were measured within 300-430 nm. A trapezoid morphology of the tips of NRs was observed. Basal stacking faults (SFs) with a density of 2.5x10⁵ cm^-1, were the major structural defects detected in the majority of NRs, whereas they seem to be far less in the long NRs.

Electron diffraction analysis showed an average (110)Si/(11-20)InGaN, [1-11]Si/[0001]InGaN orientation relationship between the two lattices, where the axial direction of most of the NRs deviated ±3-4^o around the growth direction. The influence of the interfacial structure on the divergence from the exact epitaxial orientation between the two crystal structures is examined.

Acknowledgement: Work supported under the MRTN-CT-2004-005583 “PARSEM” project.

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