Nitride semiconductors have been at the center of semiconductor research in the last decade. However Indium nitride is still poorly known, due to its growth difficulty, and its properties are still the subject of passionate debates. Still, it is clear that it is a very promising material for telecommunication optoelectronics and hyperfrequency/terahertz applications. In particular, nanostructures based on InN are extremely interesting, by combining a small bandgap, the incredible efficiency of nitride semiconductors and the tunability of quantum dots. In this paper, we present the latest advances in the growth and optical properties of InN quantum dots grown onto GaN. The optical properties of InN dots will be compared to those of InN films, and we will show that the thermal behaviour of InN dots is far superior. Using TEM and synchrotron radiation diffraction, we will analyze the strain state of the dots at the nanometer scale, along the growth axis of the dots. These results, combined with the thermodynamical analysis of the growth data, will allow us to demonstrate that the growth mechanism is not the usual Stransky-Krastanow mode, but is more related to the BCF (Burton-Cabrera-Franck) model.

The intensity of Eu-related luminescence from ion-implanted GaN with a 10 nm thick AlN cap, both grown epitaxially by metal organic chemical vapor deposition (MOCVD) is increased markedly by high-temperature annealing at 1300 degrees C. Photoluminescence (PL) and PL excitation (PLE) studies reveal a variety of Eu centers with different excitation mechanisms. High-resolution PL spectra at low temperature clearly show that emission lines ascribed to D-5(0)-F-7(2) (similar to 622 nm), D-5(0)-F-7(3) (similar to 664 nm), and D-5(0)-F-7(1) (similar to 602 nm) transitions each consist of several peaks. PL excitation spectra of the spectrally resolved components of the D-5(0)-F-7(2) multiplet contain contributions from above-bandedge absorption by the GaN host, a GaN exciton absorption at 356 nm, and a broad subedge absorption band centred at similar to 385 nm. Marked differences in the shape of the D-5(0)-F-7(2) PL multiplet are demonstrated by selective excitation via the continuum/exciton states and the below gap absorption band. The four strongest lines of the multiplet are shown to consist of two pairs due to different Eu3+ centers with different excitation mechanisms. (c) 2005 American Institute of Physics.

InN quantum dots (QDs) on GaN (0001) grown by metalorganic vapor phase epitaxy onto a sapphire substrate were studied by transmission electron microscopy (TEM). We found that the nucleation of InN QDs on GaN is directly related to the presence of threading dislocations (TDs) in the center of the QDs. The TEM analysis revealed that the TDs finish at the InN/GaN interface and they are pure edge dislocations. Therefore, spiral growth models cannot explain nucleation of these QDs. Although controlling edge TDs constitute a possible approach to determine the QD density, a better approach may be an increase in the material growth rate in order to enter the diffusion-limited growth mode, where growth is not sensitive to surface heterogeneities. (c) 2005 American Institute of Physics.

The growth of indium nitride quantum dots are studied. An investigation of the dot built-in strain, at the nanometric scale, performed using the synchrotron radiation is presented. These results are correlated with transmission electron microscopy images showing the dot structure. From these results, together with a thermodynamical analysis, it is shown that the dot growth mechanism is not the usual Stranski-Krastanov growth mode, but is more related to the BCF (Burton Cabrera Franck) growth mode.