Spontaneous Polarisation Build up in a Room Temperature Polariton Laser

We observe the build up of strong (~50%) spontaneous vector polarisation in emission from a GaN-based polariton laser excited by short optical pulses at room temperature. The Stokes vector of emitted light changes its orientation randomly from one excitation pulse to another, so that the time-integrated polarisation remains zero. This behaviour is completely different to any previous laser. We interpret this observation in terms of the spontaneous symmetry breaking in a Bose-Einstein condensate of exciton-polaritons

Hydrogen as a probe of the electronic properties of (InGa)(AsN)/GaAs heterostructures

We report on the effects of N incorporation on the electronic properties of (InGa)(AsN)/GaAs heterostructures as investigated by photoluminescence (PL) spectroscopy. PL under a magnetic field shows an increase in the electron effective mass in the N-containing material. In order to address this e.ect as well as the giant band gap reduction induced by N in (InGa)As, we exploit the ability of hydrogen to passivate the electronic activity of N in (InGa)(AsN). Such passivation is due to the formation of N–H bonds and manifests itself as: (i) a quenching of the exciton recombination in N-related complexes in the N dilute limit; (ii) a blueshift of the (InGa)(AsN) band gap toward that of the N-free material in the alloy limit. A thermal annealing leads to a complete recovery of the electronic properties (InGa)(AsN) had before H irradiation in both limits. The activation energy for the thermal dissociation, ED, of the N–H complexes follows a Gaussian distribution with a mean value increasing with the N concentration, y. Values of ED similar to those found in the alloy limit are found in the case of very dilute N concentrations (impurity limit), where dfferent N–H complexes are singled out. These results show that different N complexes are responsible for the puzzling effects exerted by N on the electronic properties of (InGa)(AsN)

Room-temperature polariton lasing in semiconductor microcavities

We observe a room-temperature low-threshold transition to a coherent polariton state in bulk GaN microcavities in the strong-coupling regime. Nonresonant pulsed optical pumping produces rapid thermalization and yields a clear emission threshold of 1 mW, corresponding to an absorbed energy density of 29 µJ cm-2, 1 order of magnitude smaller than the best optically pumped (In,Ga)N quantum well surface-emitting lasers (VCSELs). Angular and spectrally resolved luminescence show that the polariton emission is beamed in the normal direction with an angular width of ± 5deg and spatial size around 5 µm

Current status of AlInN layers lattice-matched to GaN for photonics and electronics

We report on the current properties of Al1-xInxN (x ~ 0.18) layers lattice-matched (LM) to GaN and their specific use to realize nearly strain-free structures for photonic and electronic applications. Following a literature survey of the general properties of AlInN layers, structural and optical properties of thin state-of-the-art AlInN layers LM to GaN are described showing that despite improved structural properties these layers are still characterized by a typical background donor concentration of (1–5) × 1018 cm-3 and a large Stokes shift (~800 meV) between luminescence and absorption edge. The use of these AlInN layers LM to GaN is then exemplified through the properties of GaN/AlInN multiple quantum wells (QWs) suitable for near-infrared intersubband applications. A built-in electric field of 3.64 MV cm-1 solely due to spontaneous polarization is deduced from photoluminescence measurements carried out on strain-free single QW heterostructures, a value in good agreement with that deduced from theoretical calculation. Other potentialities regarding optoelectronics are demonstrated through the successful realization of crack-free highly reflective AlInN/GaN distributed Bragg reflectors (R &gt; 99%) and high quality factor microcavities (Q &gt; 2800) likely to be of high interest for short wavelength vertical light emitting devices and fundamental studies on the strong coupling regime between excitons and cavity photons. In this respect, room temperature (RT) lasing of a LM AlInN/GaN vertical cavity surface emitting laser under optical pumping is reported. A description of the selective lateral oxidation of AlInN layers for current confinement in nitride-based light emitting devices and the selective chemical etching of oxidized AlInN layers is also given. Finally, the characterization of LM AlInN/GaN heterojunctions will reveal the potential of such a system for the fabrication of high electron mobility transistors through the report of a high two-dimensional electron gas sheet carrier density (ns ~ 2.6 × 1013 cm-2) combined with a RT mobility µe ~ 1170 cm2 V-1 s-1 and a low sheet resistance, R ~ 210 Ω/square.</sub

Determination of exciton reduced mass and gyromagnetic factor of wurtzite (inga)as nanowires by photoluminescence spectroscopy under high magnetic fields

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