We report on the MOCVD growth of InN buffer layers on sapphire substrate for InN growth. The approach used assumes that an optimized InN buffer layer has to exhibit at least the same crystalline quality and sapphire surface coverage than the GaN buffer layers allowing to grow high crystalline quality GaN on sapphire. The buffer layers were characterized by AFM and GID measurements. Sapphire nitridation was investigated: it has a strong influence on in-plane crystalline quality. Two kinds of buffer layers were optimized according to the GaN buffer layer specifications: one of them only presented In droplets at its surface. It was shown that the small amount of In droplets increases the adatoms mobility of the main layer overgrown, leading to a 25% decrease of its in-plane mosaicity, compared to InN films directly grown on sapphire. To achieve a same improvement on InN buffer layer free of In droplets, the InN main layer growth temperature had to be increased from 550 °C. to 600 °C.

We report on the use of dimethylhydrazine (DMHy) and tertiarybuthylhydrazine (TBHy), as alternative nitrogen precursor for GaN low-temperature growth, as well as to improve the InN growth rate. Lowering the GaN growth temperature, would allow growing InN/GaN heterostructures by MOVPE, without damaging the InN layers. Increasing the low InN MOVPE growth rate is of major importance to grow reasonably thick InN layers. In this respect, triethylindium (TEIn) was also used as an alternative to trimethylindium (TMIn). We demonstrate that tertiarybutylhydrazine is a suitable nitrogen source for GaN growth at 600 °C, leading to crystalline GaN layers. These layers exhibited a peak of photoluminescence emission at 3.475 eV, at 2 K, with a narrow linewidth of 18 meV; while no detectable photoluminescence was observed for layers grown with ammonia. This result opens the way to further MOVPE growth of InN and GaN based heterostructures. The unsuccessful GaN growth in a nitrogen or argon ambient using DMHy, in contrast with hydrogen, demonstrates the active role of hydrogen in the growth process. Both DMHy and TBHy were unsuitable to grow InN, but the use of TEIn instead of TMIn together with ammonia resulted at least in doubling the InN growth rate in same growth conditions

Strong coupling of multiple branches polariton in a ZnO microcavity.

We extend to any temperature, the sophisticated calculation of the evolution of the 2 K photoluminescence energy of InN proposed by Arnaudov et al. [Phys. Rev. B 69, 115216 (2004)], in view of determining the residual doping of thin films. From the detailed line shape modeling, we extract the full width at half maximum of the photoluminescence line which, in the first order, varies like n0.51 at low temperature. This allows us to propose a handy tool for rapid residual doping evaluation. Last, temperature and inhomogeneous broadening effects are analyzed. Ignoring the latter is shown to lead to an overestimation of the residual doping.

We investigate by time-resolved spectroscopy the consequences of large internal electric fields on the exciton recombination dynamics in ZnO/(Zn,Mg)O quantum wells.

Simple calculations performed in the context of linear elasticity theory, indicate that growth of InN on (hkl)-oriented substrates minimizes the density of elastic energy stored in the strained layers and boosts the critical thickness for coherent growth of strained layers to unexpected values. This renders possible to grow two-dimensional InN–GaN structures with InN layers thicknesses larger than one monolayer and, in addition, continuous in the growth plane. How impacting this finding can be for optoelectronic devices using indium nitride-based heterostructures is finally discussed.