GaN-Al0.5NGa0.5N quantum dots deposited on (11-22) planes have been grown by combining Molecular Beam Epitaxy and Metal Organic Vapour Phase Epitaxy. This combination is interesting for realization of ultraviolet operation light emitting diodes, lasers andsingle photon sources,… (1,3) The growth of dots was achieved by MBE using ammonia as nitrogen precursor and growth interruption in ammonia less conditions to trigger corrugation of GaN and dot formation (4). The (11-22) GaN oriented peudosubstrate was realized by MOVPE starting from a M-plane oriented sapphire substrate. The orientation of the growth plane dictates in-plane anisotropies which are effectively found leading to a transition from isolated dots to nanochains - oriented along the <1-100> direction as evidenced from Atomic Force Microscopy features or optical properties: polarization rates and temperature dependent measurements of the radiative recombination process for instance(5). We here restrict to small size isolated quantum dots and present innovative optical properties among which are micro-photoluminescence data versus pump power, polarization of the emitted photons at different temperatures. We also analyse the photoluminescence decay times and model our finding in the context of the effective mass approximation. The crystal field splitting is measured in Al 0.5NGa 0.5N lattice-matched to (11-2) oriented GaN by polarized microphotoluminecence under high photo- injection conditions.

Deep ultra-violet semiconductor lasers have numerous applications for optical storage, biochemistry or optical interconnects. UV-emitting ridge lasers usually embed nitride heterostructures grown on complex buffer layers or expensive substrates – an approach that cannot be extended to nano-photonics and microlasers. We demonstrate here the first deep ultra-violet microlaser operating at 275nm at room temperature under optical pumping. It is based on binary GaN/AlN thin quantum wells (QWs) grown on a silicon substrate and embedded in microdisk resonators. Those QWs indeed combine UV-C emission with a good emission efficency even at room temperature thanks to the huge band offset beetwen GaN and AlN. They form the active layer of state-of-the-art microdisk resonators, which electromagnetic modes, the so-called Whispering-Gallery Modes (WGMs), present a low modal volume and a high quality factor (Q=6000). This active layer can form free-standing membranes and is further compatible with future developments of nitride nanophotonic platforms on silicon.

Self-assembled semiconductors QDs are of great interest in fundamental physics as well as inapplied physics. In GaN/AlN heterostructures, the huge band-offset and the strong excitonicbinding lead to an important exciton confinement allowing an emission even at roomtemperature. GaN QDs grown along the (1000) axis are named “polar” due to their stronginternal electic field which lead to the so-called QCSE. The most important modifications due tothis electric field take place in thick QDs emitting around 330nm and more : the luminescence isredshifted and the radiative lifetime is strongly increased [1]. On the other hand, in thin QDs(smaller than 2.3nm), the quantum confinement plays the key role, thus leading to a significantlysmaller homogeneous linewidth and to the resolution of the exciton fine-structure splitting[2]. Concerning the radiative recombination processes, several papers reported measurements at330nm or more either in polar[3] or non-polar[4] nanostructures. Experimental data on excitonicradiative lifetime are also existent in thin QDs but on a limited dynamical range where thepossible influence of QCSE is not discussed [5].In this work, we report time-resolved photoluminescence measurements in GaN/AlN QDsemitting between 280nm and 360nm. For QDs emitting at 300nm we observe a biexponentialdecay dynamics of the photoluminescence signal (Fig.1, left). The fast component (450 ps) isinterpreted as the radiative lifetime of the QDs in the absence of a noticeable redshift of thetransition. Thanks to our better signal-to-noise ratio than in Ref. 5, we are able to extract a slowcomponent (2 ns) which may originate either from feeding from the barrier or other processesinside the QD. Power dependent experiments further confirm this interpretation. We observe thatthe fast component remains the same as a function of excitation power (Fig.1, right) and, moreimportantly, that the intensity ratio keeps the same value. This rules out any contribution fromthe relaxation of multi-carriers complexes such as biexciton or trion in the short time dynamics

Single-walled carbon nanotubes are one-dimensional nanostructures where the Coulomb interactions between charge carriers are strongly enhanced compared to systems of higher dimensionality. This results in an electron-hole bound state -the so-called exciton- with a binding energy of the order of one third of the bandgap, which controls the SWNTs optical properties. I will review the importance of the exciton-exciton interactions in SWNTs in the light of the exciton recombination dynamics, the excitonic collision broadening, and the biexciton.

Single-walled carbon nanotubes are one-dimensional nanostructures where the Coulomb interactions between charge carriers are strongly enhanced compared to systems of higher dimensionality. This results in an electron-hole bound state -the so-called exciton- with a binding energy of the order of one third of the bandgap, which controls the SWNTs optical properties. I will review the importance of the exciton-exciton interactions in SWNTs in the light of the exciton recombination dynamics, the excitonic collision broadening, and the biexciton.

At low temperature the photoluminescence of single-wall carbon nanotubes show a large variety of spectral profiles ranging from ultra narrow lines in suspended nanotubes to broad and asymmetrical line-shapes that puzzle the current interpretation in terms of exciton-phonon coupling. Here, we present a complete set of photoluminescence profiles in matrix embedded nanotubes including unprecedented narrow emission lines. We demonstrate that the diversity of the low-temperature luminescence profiles in nanotubes originates in tiny modifications of their low-energy acoustic phonon modes. When low energy modes are locally suppressed, a sharp photoluminescence line as narrow as 0.7 meV is restored. Furthermore, multi-peak luminescence profiles with specific temperature dependence show the presence of confined phonon modes.

Properties of self-assembled quantum dots (QDs), often referred to as artificial atoms in solid state, are very interesting in order to study physical effects specific to single quantum systems such as the single-photon emission. Thanks to their huge vertical quantum confinement, GaN QDs are emitting even at room temperature and on a large UV range. This peculiarity makes GaN QDs good candidates for fundamental physics as well as conception of devices such as UV-LEDs. In so-called thick QDs (height larger than 2.3 nm), the energies of the confined electronic states are determined by the quantum confined Stark effect. On the contrary, in thin QDs (height smaller than 2.3 nm) the quantum confinement plays the major role, thus leading to a significantly smaller homogeneous linewidth and to the resolution of the exciton fine-structure splitting [Kindel, PRB81, 241309]. As far as time-resolved measurements are concerned, several papers reported experiments in thick QDs emitting at 350nm or more, either in polar [Bretagnon, PRB73, 113304] or non-polar nanostructures [Founta, APL86, 171901]. We report photoluminescence decay time measurements in thin GaN QDs emitting between 280nm and 360nm. For QDs emitting at 290nm we observe a monoexponential decay and the abscence of any red shift for the luminescence spectrum shows that we are in the regime of a single electronhole pair per dot. In this case, we measure the intrinsic radiative recombination time, without any perturbation due to the Stark effect. We find a radiative lifetime of about 350 ps in good agreement with our theoritical model.