Publications de Jean-Louis Staehli

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Microcavity exciton polaritons, the fundamental optical excitations of semiconductor microcavities with quantum wells inside, have been proposed as promising candidates for observing stimulated scattering, condensation and other phenomena related to the bosonic nature of excitons. Having a light mass, quantum degeneracy of polaritons can be reached at low densities and high temperatures. But the radiative time of polaritons is very short (in the picosecond range) and usually prevents an efficient thermaliza

Modifying the photonic environment of a semiconductor quantum well by embedding it in a high-reflectivity microcavity gives rise to new fundamental optical excitations, half-quantum well excitons, half-photons. These particles, called polaritons, have a light mass, as cavity photons, meaning that they have a large De Broglie wavelength. On the other hand, polaritons, like excitons, are subject to Coulomb interaction, a feature generating strong optical nonlinearities. Such properties favour quantum degenera

We demonstrate three-dimensional spatial confinement of exciton-polaritons in a semiconductor microcavity. Polaritons are confined within a micron-sized region of slightly larger cavity thickness, called mesa, through lateral trapping of their photon compo ...

We report on luminescence, transmission and luminescence excitation measurements on indirect-gap AlxGa1-xAs in the composition range 0.42 less than or equal to x less than or equal to 0.86. The phonon coupling strength in transitions of bound excitons is investigated and found to be dependent on AlAs mole fraction and on the chemical species of the binding impurity. We find binding energy values of 35.5 +/- 5.5 meV for x = 0.42 and 50.0 +/- 5.5 meV for x = 0.86. The recombination of indirect-gap free excito

V groove GaAs/AlGaAs quantum wires are investigated by spatially resolved photoluminescence spectroscopy using a low-temperature scanning near- field optical microscope. The spectra along the wires feature several sharp emission lines, which are understood as the emission from exciton states localized in inhomogeneities of the confining potential. It is expected that these exciton states spatially overlap and that their energies are correlated, which leads to level repulsion. The statistical analysis of the

Our investigations focus on low-temperature luminescence experiments on a set of type-II GaAs/AlAs multiple-quantum-well (MQW) samples grown by low-pressure metal-organic vapor-phase epitaxy. The layered structures consists of 50 periods of either 2 monolayers (ML), 4, 5, 6, or 7 ML GaAs embedded in 28 ML AlAs. For (001) GaAs substrates, 6 degrees misoriented towards the nearest (111) plane of group-V atoms, monolayer steps at the AlAs/GaAs interfaces with regular terrace widths (2.7 nm) can be seen by high

Type-II GaAs/AlAs multiple-quantum well samples groan by low-pressure metal-organic vapour-phase epitaxy have been investigated. The layered structures consist of 50 periods of either 2 monolayers (ML), 4 ML. 5 ML, 6 ML, or 7 ML GaAs embedded in 28 ML AlAs. Using (100) GaAs substrates 6 degrees misoriented towards the nearest (111)B plane monolayer steps at the AlAs/GaAs/AlAs interfaces with regular terrace widths (2.7 nm) can be seen by high-resolution transmission electron microscopy. In the photoluminesc

Cavity polaritons, the elementary optical excitations of semiconductor microcavities, may be understood as a superposition of excitons and cavity photons(1). Owing to their composite nature, these bosonic particles have a distinct optical response, at the same time very fast and highly nonlinear. Very efficient light amplification due to polariton-polariton parametric scattering has recently been reported in semiconductor microcavities at liquid-helium temperatures(2-11). Here we demonstrate polariton param

InP films have been deposited on amorphous sapphire substrate by means of the metallorganic chemical vapour deposition technique with and without PH3/H-2 plasma preactivation. Polycrystalline materials, having average grain sizes of about 40 nm, which, however, vary according to the growth parameters, were obtained. The structural and compositional disorder strongly influence the optical and electrical properties. The most structurally disordered films present the largest photoluminescence (PL) efficiency a

The spontaneous and stimulated emissions of strongly excited GaAs/(Ga,Al)As quantum wells are investigated in the one-dimensional optical amplifier geometry, using the variable-stripe-length method. The optical amplification and its saturation are studied by monitoring the spectra of spontaneous and amplified luminescence as a function of the position on the stripe. The deduced experimental spatial dependences of carrier and luminous densities are found to agree in a semiquantitative way with the numerical

The results obtained from luminescence measurements made on one-dimensional optical amplifiers are reviewed. The investigated samples are GaAs/(Ga, Al)As waveguiding structures containing a multiple quantum well structure as active element. The experimental data are compared with the results of a numerical self-consistent model of the optical amplifier. The observed spatial dependencies of carrier and luminous densities are found to agree in a semi-quantitative way with the theoretical predictions. Saturati

We report on an investigation of the electron-hole (e-h) plasma decay time tau(tot) versus e-h pair density in semiconductor quantum wells. We determine the density reached in a steady-state photoluminescence experiment from the optical spectra and compare it with the e-h pair generation rate. We find that in our samples only radiative e-h recombination is important, and that nonradiative processes and plasma expansion have negligible effects on tau(tot). At plasma densities larger than 5 x 10(12) cm-2, we

We investigate a GaAs/(Ga,Al)As Fabry-Perot microcavity, into which (In,Ga)As quantum wells have been inserted. The cavity is wedge shaped, i.e., the detuning between the bare-exciton resonance and the bare optical cavity mode depends on the spatial position on the sample. Linear transmission spectra reveal a well-resolved Rabi splitting of 8 meV at resonance, an inhomogeneously broadened exciton transition of 4-5-meV width, and an 0.7-meV-wide Fabry-Perot mode. The time-resolved transmission exhibits deep

We present a comparison between the predictions of two theoretical models and experimental results on ultrathin GaAs layers with a thickness in the range from 1 to 8 ML embedded in bulk (AlxGa1-x)As, 0.30 less than or equal to x less than or equal to 0.34. The theoretical predictions, obtained from an empirical tight-binding Green's-function approach and from the usual effective-mass approximation, are compared to photoluminescence and photoluminescence excitation data of a set of multiple quantum-well samp

Near-field optical spectroscopy is used to investigate the effects of disorder in the optical processes in semiconductor quantum wires. We observe photoluminescence emissions from extended, delocalized excitons at low temperatures (5 K) and low excitation densities. Combining high spectral and spatial resolution, we isolate homogeneous emission lines from excitons delocalized over distances up to 600 nm in the fundamental state. The energies of the emissions are consistent with different quantum spatial con

Amongst the new precursors for the III component in MOVPE there are numerous nitrogen containing compounds. Using those compounds, besides the electrical and optical quality of the grown material, the question of incorporation of nitrogen arises. We present the results of GaP growth with the TMGa-TMN adduct. Photoluminscence at 2 K clearly detects nitrogen as a substitutional dopant. Considering the luminescence features the nitrogen concentration was estimated to be about 10(16)-10(17) cm-3. The residual c

We present a systematic study of the oscillator strength of the positively charged excitons (X+) in Cd1-xMnxTe quantum wells. CW-absorption and time-resolved photoluminescence measurements were combined as two approaches for the determination of the oscillator strength. By varying (in a small magnetic field) the spin subband hole distribution at constant total concentration, we observe an increase of the oscillator strength in absorption, proportional to the hole concentration in one spin subband (the one w

Detailed investigation of the luminescence features due to the recombination of the exciton-free-carrier process in GaSe is presented. This process shows a well-resolved luminescence line and it is an efficient recombination process in this semiconductor, even at low temperatures. We report accurate photoluminescence spectra measured at 2 K as a function of the excitation intensity, of the excitation energy, and of the lattice temperature from 2 to 200 K. To discriminate between the different kinds of free

We present an investigation of the optical gain and its saturation of the electron-hole plasma confined in GaAs/(Ga,Al)As quantum wells. For such investigations the variable stripe length method is a simple but quite powerful tool. The spacial longitudinal variation of luminous and electron-hole pair densities in narrow stripes of various lengths has been investigated theoretically and experimentally. For this also the spectra of spontaneous luminescence (emitted in a direction perpendicular to the stripe)

Jean-Louis Staehli

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Towards a room-temperature polariton amplifier

Polariton amplification in semiconductor microcavities

Polariton parametric amplification in semiconductor microcavities

Engineering the spatial confinement of exciton polaritons in semiconductors

Indirect-gap AlxGa1-xAs and its similarity to GaP

Exciton relaxation and level repulsion in GaAs/AlxGa1-xAs quantum wires

Blue luminescence from ultrathin GaAs layers embedded in AlAs

Ultrathin GaAs layers embedded in AlAs: The observation of intense short-wavelength emission

High-temperature ultrafast polariton parametric amplification in semiconductor microcavities

Luminescence study of the disorder in polycrystalline InP thin films

Optical Amplification and Its Saturation in Semiconductor Quantum-Wells

Saturation and Losses in an Optical Semiconductor Quantum-Well Amplifier

Density Dependence of Electron-Hole Plasma Lifetime in Semiconductor Quantum-Wells

Coherent exciton-photon dynamics in semiconductor microcavities: The influence of inhomogeneous broadening

Optical properties of ultrathin GaAs layers embedded in AlxGa1-xAs

Near-field imaging of one-dimensional excitons delocalized over mesoscopic distances

Movpe Growth and Properties of Gap Using Nitrogen Bridged Adduct

Oscillator strengths of charged excitons: combining magnetoabsorption and photoluminescence dynamics in semimagnetic quantum wells

Exciton-Carrier Scattering in Gallium Selenide

Optical Amplification and Its Saturation in Semiconductor Quantum-Wells