Indium nitride (InN) quantum dots have been grown on gallium nitride (GaN) templates with heights of 10 and 20 nm. The authors demonstrate that the surface densities of the dots are strongly affected by the nature of the carrier gas used during the growth, which can be used to modulate the surface density. The authors show here that replacing nitrogen by helium leads to a decrease of the dot surface density, while argon induces a strong increase of the density. Although validated for the InN/GaN system, this approach has a more general scope and can be extended to other material systems. (c) 2007 American Institute of Physics.

A transmission electron microscopy study of the misfit dislocation (MD) networks between InN quantum dots (QDs) and GaN substrate/capping layer is presented. Applying the geometric phase algorithm in planar-view orientation, a complete characterization of the first interface shows a set of three families of 60 degrees MDs lying along the three < 11 (2) over bar0 > directions without node formation. The growth of a GaN capping layer decreases the plastic relaxation degree of the InN QDs by a rearrangement of the MDs. The full relaxation of the capping layer suggest that no changes will occur in the QD strain state during later growths. (C) 2007 American Institute of Physics.

A complete characterization of dislocation network in a highly mismatched interface with high spatial resolution has been performed. The interface between InN quantum dots and a (0001) GaN substrate contains three noninteracting sets of regularly-spaced misfit dislocations lying along < 11 (2) over bar0 > directions. The network has a "Star of David" form, with each star bounding a hexagonal region which is pseudomorphic. These misfit dislocations form a threading dislocation network at the island edges due to free surface forces.

The initial growth of InN grown by MOVPE was investigated by a combination of atomic force microscopy (AFM) and X-ray specular reflectivity for five different thin films ranging from 57 to 750 angstrom. Both AFM and specular reflectivity measurements show that during the initial growth the surface is not completely covered but that instead a discontinuous layer resembling quasi two-dimensional islands is formed. Dots with heights between 30 and 100 nm appear at the same time; the number density of these dots decreases with increasing thickness. At 750 angstrom the surface is completely covered and obtains a granular aspect. The surface coverage of the discontinuous wetting layer is discussed in relation with the apparent porosity calculated from the specular reflectivity data

We evaluate the properties of nitride heterostructures on semipolar substrates using two indicators: the cancellation of the Quantum Confined Stark Effect and the volume density of elastic energy stored in the strained layers of GaN-GaInN heterostructures lattice-matched to (hkl)-oriented GaN semipolar substrates. These two parameters indicate that the growth on specific orientations is a plus when compared to growth on (0001) polar substrates. We will show that, unfortunately, one cannot simultaneously minimize the stored elastic energy and cancel the Quantum Confined Stark Effect, but it is possible to significantly reduce both of them. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.