We report exciton-polariton condensation in a new family of fully hybrid ZnO-based microcavity demonstrating the best-quality ZnO material available (a bulk substrate), a large quality factor (~4000) and large Rabi splittings (~240 meV). Condensation is achieved between 4 and 300 K and for excitonic fractions ranging between 17% and 96%, which corresponds to a tuning of the exciton-polariton mass, lifetime, and interaction constant by 1 order of magnitude. We demonstrate mode switching between polariton branches allowing, just by controlling the pumping power, to tune the photonic fraction by a factor of 4.

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The incorporation of metal atoms into silicon nanowires during metal-particle-assisted growth is a critical issue for various nanowire-based applications. Here we have been able to access directly the incorporation and redistribution of metal atoms into silicon nanowires produced by two different processes at growth rates ranging from 3 to 40 nm s À 1 , by using laser-assisted atom probe tomography and scanning transmission electron microscopy. We find that the concentration of metal impurities in crystalline silicon nanowires increases with the growth rate and can reach a level of two orders of magnitude higher than that in their equilibrium solubility. Moreover, we demonstrate that the impurities are first incorporated into nanowire volume and then segregate at defects such as the twin planes. A dimer-atominsertion kinetic model is proposed to account for the impurity incorporation into nanowires.

We report on a new type of optical nonlinearity in a polariton p-i-n microcavity. Abrupt switching between the strong and weak coupling regime is induced by controlling the electric field within the cavity. As a consequence bistable cycles are observed for low optical powers (2-3 orders of magnitude less than for Kerr induced bistability). Signatures of switching fronts propagating through the whole 300 x 300 µm 2 mesa surface are evidenced.PACS numbers: 71.36.+c, 42.65.Pc, 73.50.Pz, 78.55.Cr After its first observation in a Fabry Perot cavity containing Na vapor [1], optical bistability has been widely explored in solid state systems for its possible application in all optical circuits and optical computing [2]. A common approach is the use of a microcavity in which the resonance frequency depends on the stored optical energy: optical χ (3) nonlinearities, of electronic or thermal origin, have been used to obtain bistability in 1-dimensional [3,4] and 2 dimensional [5,6] photonic devices, with switching incident powers around 1 kW/cm 2 . When part of a spatially extended bistable system is switched from one stable state to the other, a front is formed between spatial regions in different states. If this front is locked, spatial solitons can be observed [7,8], otherwise the front propagates along the surface until the whole sample has switched state [9]. Recently optical bistability of microcavity polaritons has been theoretically proposed to generate propagation of switching fronts which can be used for all optical computation [10]. Polaritons are mixed exciton-photon quasiparticles resulting from the strong coupling regime of excitons with a resonant cavity mode [11]. Polaritonpolariton scattering gives rise to giant χ (3) -type nonlinearities [12,13] which have been recently shown to generate optical bistability [14]; indications of spatial solitons were also reported [15]. Another approach for optical bistability is to use the switch from strong to weak coupling regime due to exciton bleaching at high pumping power [16,17]. This method has been theoretically proposed in 1996 [18], and some experimental indication has been reported in 2004 [19]. In this work, we experimentally demonstrate low-power optical bistability based on a new non-linear mechanism. Switching between strong and weak coupling regime is induced controlling the internal electric field of a p-i-n microcavity. Well defined hysteresis cycles are observed both scanning the external bias or the optical power. * now at CNISM UDR Pavia and Dipartimento di Elettronica, Università degli studi di Pavia, via Ferrata 1, 27100 Pavia, Italy A model including the changes of optical and electronic properties between the strong and weak coupling regime is developed and gives a good overall description of the observed cycles. Finally we show that a local excitation can produce commutation of the whole mesa. The sample (see Fig. 1 a)) is described in details in ref. [20]. Grown on an n-doped GaAs substrate, an undoped GaAs cavity containing 3 In 0.05 Ga 0....

International audienceWe demonstrate polariton lasing in a bulk ZnO planar microcavity under non-resonant optical pumping at a small negative detuning (delta~-1/6 the 130 meV vacuum Rabi splitting) and a temperature of 120 K. The strong coupling regime is maintained at lasing threshold since the coherent nonlinear emission from the lower polariton branch (LPB) occurs at zero in-plane wavevector well below the uncoupled cavity mode. The contribution of multiple localized polariton modes above threshold and the non-thermal polariton statistics show that the system is in a far-from-equilibrium regime, likely related to the moderate photon lifetime and in-plane photonic disorder in the cavity

International audienceUp-scaling silicon nanowire (SiNW)-based functionalities requires a reliable strategy to precisely position and integrate individual nanowires. We here propose an all-in-situ approach to fabricate self-positioned/aligned SiNW, via an in-plane solid-liquid-solid growth mode. Prototype field effect transistors, fabricated out of in-plane SiNWs using a simple bottom-gate configuration, demonstrate a hole mobility of 228 cm2/V s and on/off ratio >103. Further insight into the intrinsic doping and structural properties of these structures was obtained by laser-assisted 3 dimensional atom probe tomography and high resolution transmission electron microscopy characterizations. The results could provide a solid basis to deploy the SiNW functionalities in a cost-effective way

Cavity polaritons have been shown these last years to exhibit a rich variety of non-linear behaviors which could be used in new polariton based devices. Operation in the strong coupling regime under electrical injection remains a key step toward a practical polariton device. We report here on the realization of a polariton based light emitting diode using a GaAs microcavity with doped Bragg mirrors. Both photocurrent and electroluminescence spectra are governed by cavity polaritons up to 100 K. PACS numbers: 71.36.+c, 78.60.Fi, 73.50.Pz, 78.55.Cr As first predicted by Purcell in 1946 [1], spontaneous emission of light can be strongly modified when inserting an emitter in a resonant cavity. When the emitter is located at an antinode of the electromagnetic field, the emission of light can be strongly accelerated or even become reversible if the light-matter coupling is strong enough. In such strong coupling regime, the degeneracy between the emitter and the photon mode is lifted giving rise to two light-matter entangled eigenstates spectrally separated by the Rabi splitting. This strong coupling regime has been first evidenced for atoms in ultra-high finesse microcavities [2] and more recently in various solid state systems like a superconducting q-bit[3], quantum well excitons in inorganic [4] or organic semiconductors [5], intersubband transition in two dimensional electron gas [6] or excitons in single quantum dots [7,8,9]. Cavity polaritons, resulting from the strong coupling regime between excitons in quantum wells and cavity photons, have been the subject of intensive research since their discovery in 1992 [4]. In two dimensional cavities, each exciton with a given in-plane wave vector k // is coupled to the photon mode with the same k // . The strong coupling regime gives rise to two polariton branches with a pronounced energy trap of the lower branch close to k // = 0 [10]. The bosonic nature of polaritons in addition to the strong polariton-polariton interactions are responsible for a rich variety of non-linear behaviours in inorganic materials: polariton accumulation in the ground state and formation of a macroscopically occupied coherent state [11,12,13,14,15], photon pair emission [16] or spin current generation [17]. These features are promising for future quantum applications but have up to now only been observed under optical pumping. Electrical injection of these entangled light-matter states is a key step toward the implementation of practical, compact devices. So far electrical injection of cavity polaritons has been reported only in organic semiconductors [18] where the coupling strength is very large (Rabi splitting of several hundreds of meV). More recently indications of electrical injection of polaritons using intersubband transitions in GaAs have been claimed [19]. However to our knowledge non-linearities have not been observed using either of these schemes. The GaAs system, when relying on interband transitions, is very attractive since its strong non-linearities could be exploited in a...

Energy dispersive x-ray (EDX) spectroscopy coupled to transmission electron microscopy (TEM) is used to analyze the passivation layer deposited on the sidewall of InP submicron patterns etched in Cl2–H2 and HBr inductively coupled plasmas. It is shown that a thin Si-containing layer is deposited on the sidewalls of the etched patterns, resulting from the reaction of Cl2 or HBr with the Si wafer used as the sample tray. For Cl2-containing plasma, the deposition layer becomes thicker when hydrogen is added to the gas mixture, leading to highly anisotropic InP etching at an optimized H2 percentage. A similar effect is obtained in HBr plasma by increasing the ICP power. When O2 is added to the gas mixture, the deposited layer is changed from Si rich to more stoichiometric silicon oxide (SiO2) and the passivation effect is enhanced. EDX-TEM analysis has also been carried out on InP samples etched in Cl2–N2 plasma for comparison. A similar impact of the coverplate material on the sidewall profile is evidenced, the InP sidewall being moreover strongly In deficient in this case. These results give useful guidelines to define anisotropic etching processes scalable to large-diameter InP wafers.