Low temperature reflectivity study of ZnO/(Zn,Mg)O quantum wells grown on M-plane ZnO substrates

We report growth of high quality ZnO/Zn0.8Mg0.2O quantum well on M-plane oriented ZnO substrates. The optical properties of these quantum wells are studied by using reflectance spectroscopy. The optical spectra reveal strong in-plane optical anisotropies, as predicted by group theory, and marked reflectance structures, as an evidence of good interface morphologies. Signatures ofc onfined excitons built from the spin-orbit split-off valence band, the analog of exciton C in bulk ZnO are detected in normal incidence reflectivity experiments using a photon polarized along the c axis of the wurtzite lattice. Experiments performed in the context of an orthogonal photon polarization, at 90^{\circ}; of this axis, reveal confined states analogs of A and B bulk excitons. Envelope function calculations which include excitonic interaction nicely account for the experimental report

Transport of indirect excitons in ZnO quantum wells

We report on spatially- and time-resolved emission measurements and observation of transport of indirect excitons in ZnO/MgZnO wide single quantum wells

High quality factor nitride-based optical cavities: microdisks with embedded GaN/Al(Ga)N quantum dots

We compare the quality factor values of the whispery gallery modes of microdisks incorporating GaN quantum dots (QDs) grown on AlN and AlGaN barriers by performing room temperature photoluminescence (PL) spectroscopy. The PL measurements show a large number of high Q factor (Q) resonant modes on the whole spectrum which allows us to identify the different radial mode families and to compare them with simulations. We report a considerable improvement of the Q factor which reflect the etching quality and the relatively low cavity loss by inserting QDs into the cavity. GaN/AlN QDs based microdisks show very high Q values (Q > 7000) whereas the Q factor is only up to 2000 in microdisks embedding QDs grown on AlGaN barrier layer. We attribute this difference to the lower absorption below bandgap for AlN barrier layers at the energies of our experimental investigation

Laser emission with excitonic gain in a ZnO planar microcavity

The lasing operation of a ZnO planar microcavity under optical pumping is demonstrated from T=80 K to 300 K. At the laser threshold, the cavity switches from the strong coupling to the weak coupling regime. A gain-related transition, which appears while still observing polariton branches and, thus, with stable excitons, is observed below 240K. This shows that exciton scattering processes, typical of II-VI semiconductors, are involved in the gain process

Relaxation and emission of Bragg-mode and cavity-mode polaritons in a ZnO microcavity at room temperature

The strong coupling regime in a ZnO microcavity is investigated through room temperature photoluminescence and reflectivity experiments. The simultaneous strong coupling of excitons to the cavity mode and the first Bragg mode is demonstrated at room temperature. The polariton relaxation is followed as a function of the excitation density. A relaxation bottleneck is evidenced in the Bragg-mode polariton branch. It is partly broken under strong excitation density, so that the emission from this branch dominates the one from cavity-mode polaritons

Etude des defauts d'irradiation electroniques dans InP type p

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Physique des Semiconducteurs et des Composants Electroniques - Problèmes Résolus.: Complément pratique de l'ouvrage "Physique des semiconducteurs et des composants électroniques". - 2e et 3e cycles, écoles d'ingénieurs.

National audienceCe recueil de 42 problèmes résolus complète le cours Physique des semiconducteurs et des composants électroniques de Henry Mathieu. Les problèmes sont répartis en cinq parties : la première aborde les différents phénomènes et effets physiques qui régissent les caractéristiques des électrons dans les semiconducteurs ; la deuxième est consacrée aux composants bipolaires et aux propriétés de la jonction pn qui constitue la structure de base de ces composants ; la troisième partie traite des composants unipolaires avec les hétérostructures (contact métal /semiconducteur ; métal /isolant / semiconducteur) ainsi que des composants actifs, tels que les différents types de transistors à effet de champ ; dans la quatrième partie le domaine important des composants optoélectroniques est abordé en traitant les phénomènes d'interaction du rayonnement avec le semiconducteur et avec les cellules photoconductrices, photodiodes, cellules solaires, diodes électroluminescentes et diodes lasers ; la dernière traite des effets quantiques rencontrés dans les hétérostructures semiconductrices. Certains problèmes, dont la résolution est numérique, permettent de comparer les solutions exactes des équations aux solutions approchées. Les programmes utilisent le logiciel Maple V

Barrier composition dependence of the internal electric field in ZnO∕Zn1−xMgxO quantum wells.

International audienceTime-integrated photoluminescence experiments are used to study the excitonic optical recombinations in wurtzite ZnO∕Zn1−xMgxO single quantum wells of varying widths and magnesium compositions. By comparing experimental results with a variational calculation of excitonic energies, the authors determine the magnitude of the built-in electric field that is induced by both spontaneous and piezoelectricpolarizations. It is found that the electric field varies linearly with magnesium composition. By taking into consideration the well-known distribution of electric field among the barrier and the well layers in multiquantum wells, the authors show that their results are fully consistent with previously reported data

Evidence de l'interaction dipôle-dipôle dans la photoluminescence résolue en temps des boîtes quantiques GaN/AlN.

National audienc

Time-resolved spectroscopy of excitonic transitions in ZnO/(Zn, Mg)O quantum wells

International audienceWe report on the optical spectroscopy of a series of ZnO/(Zn, Mg)O quantum wells of different widths, using time-resolved photoluminescence. The samples were grown by molecular beam epitaxy on ZnO templates, themselves deposited on sapphire substrates. The barriers consist of Zn0.78Mg0.22O layers. The presence of large internal electric fields in these quantum wells results in a competition between quantum confinement and the quantum confined Stark effect as the quantum well width is varied. A transition energy lying 0.5 eV below the ZnO excitonic gap was observed for the widest of our wells. The PL spectra of the wide quantum wells were obtained using time-integrated photoluminescence, taking a great care with screening effects induced by their very slow dynamics. The effect of the built-in electric field on the excitonic properties was investigated. The excitonic fine structure is shown to depend strongly on the enhancement or suppression of the exchange interaction as a function of the quantum well width