Exciton-polariton Emission Research Articles

Novel Approach to Tuning the Physical Properties of Organic-Inorganic Hybrid Semiconductors

We discuss theoretically a novel approach to tailoring the properties of a new family of organic-inorganic hybrid superlattices, using two isostructural materials, ZnSe(en)0.5 and ZnTe(en)0.5, as examples. Replacing Se with Te leads to a number of nontrivial changes: the conduction band parity, singularity type, conductivity in the superlattice direction, and the p-type dopability. Experimentally, we report the first unambiguous observation of exciton-polariton emission in a hybrid semiconductor, i.e., ZnTe(en)0.5 . The band-edge excitonic transitions in both emission and absorption are explained by the calculated electronic structures.

Linear polarisation inversion: A signature of Coulomb scattering of cavity polaritons with opposite spins

The polarisation of exciton-polariton emission is used to determine parameters of the interaction Hamiltonian of cavity polaritons. Linear polarisation of the polariton emission under linearly polarised excitation is theoretically analysed and shown to be determined by the ratio of the interaction strengths of polaritons with opposite and parallel spins. The experimentally observed inversion of the linear polarisation of the emission with respect to that of the exciting light indicates the dominant role of the exchange interaction in the polariton-polariton scattering. A comparison with the theory yields the sign of the term in the Hamiltonian describing the interaction of two polaritons with opposite spins, as well as its relative value with respect to the main term responsible for the scattering of polaritons with parallel spins. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Exciton polariton emission from a resonantly excited GaAs microcavity

Coherent emission efficiency in a 100A GaAs SQW microcavity was enhanced one order when pumped resonantly at 10 K, compared to the off-resonant excitation. The usual kink observed in the exciton emission linewidth as well as in the emission intensity in relation to the pump power, changes smoothly instead of the usual abrupt kink observed in the off-resonant microcavity laser. In addition, polarization measurements show a correlation relationship between the pump light polarization and the cavity emission polarization.

Time-resolved and cw photoluminescence from strongly coupled organic microcavities

The optical properties of microcavities (MCs) are strongly dependent on both polarization of incident and emitted light and its angle of observation. Here we report the measurements of cw- and time-resolved photoluminescence (PL) observed at negative detuning and at resonance for s- and p-polarization in the strong coupling regime of a planar MC containing J-aggregates of a cyanine dye. Following non-resonant excitation, the emission spectra consist of three types of features: direct J-aggregate exciton emission, polariton emission, and uncoupled monomer emission through the transmission maxima of the distributed Bragg reflector beyond the stop-band. We compare our experimental results with a transfer-matrix calculation of the transmission for s- and p-polarization and explain the different positions of the polariton branches, the stop-band width, and the high- and low energy transmission maxima of the MC. Time-resolved PL experiments show an increase in the decay lifetime of the exciton-like mode when it is positioned far from the cavity mode. Close to resonance, the lower polariton branch decays with the natural lifetime of the J-aggregates.

Temperature-dependent exciton polariton photoluminescence in ZnO films

The polarized photoluminescence (PL) in a (0001) oriented ZnO epitaxial film is studied in the temperature range 4.5-250 K. We report the evidence of exciton polariton emission between 50 and 130 K ...

Measurement of the intensity and phase of microcavity exciton-polariton emission in the linear and nonlinear regimes

Measurement of the intensity and phase of microcavity exciton-polariton emission in the linear and nonlinear regimes

Phonon-assisted exciton–polariton emission in a microcavity

Quantum-well excitons in a semiconductor microcavity are studied by photoluminescence and input–output experiments. Emission peaks at both longer and shorter wavelengths are observed, indicating the importance of exciton –acoustic-phonon interaction at low temperature. Pump–probe experiments show that the probe beam can be either amplified or attenuated, depending on the energies of the pump and the probe. The dynamics of this process are described by a simple rate-equation model.

Observation of exciton-polariton oscillating emission in a single-quantum-well semiconductor microcavity.

We have observed direct time domain exciton-polariton oscillating emission from a single-quantum-well GaAs microcavity. Observed oscillation periods of 21.7 ps were in good agreement with the spectral splitting of 0.12 nm. Such observations are consistent with the view that recently observed thresholdless coherent emission is not resonant Rayleigh scattering but rather exciton-polariton emission.

Quantum electrodynamic effects in semiconductor microcavities - Microlasers and coherent exciton-polariton emission

We discuss the spontaneous emission of quantum well excitons in a monolithic microcavity. When the quantum well is excited by a nonresonant pump wave at high above the bandgap, the incoherent spontaneous emission is concentrated on the single resonant mode and the laser threshold is reduced by many orders of magnitude. When the quantum well exciton is excited by a resonant pump wave, the coherent spontaneous emission based on a «microcavity exciton-polariton» is observed. The spectral linewidth and the polarization of the pump wave are preserved and the coupling efficiency into the single resonant mode approaches 100%. The microcavity-induced normal mode splitting is observed in the frequency domain by photoexcitation spectrum measurements and in the time domain by pump-probe measurements

Quantum-well exciton polariton emission from multi-quantum-well wire structures

The radiative decay of quantum-well exciton (QWE) polaritons in microstructured Al 0.3 Ga 0.7 As - GaAs multi-quantum wells (MQW) has been studied by photoluminescence spectroscopy. Periodic wire structures with lateral periodicities a = 250–500 nm and lateral widths t = 100–200 nm have been fabricated by plasma etching. The thickness of the QWs was 13 nm. In the QW wire samples the free-exciton photoluminescence was strongly reduced and the QWE polariton emission was observed as a maximum peaked at a 3 meV higher energy than the free QWE transition. In samples which had only a microstructured cladding layer, the free-exciton photoluminescence was dominant in the spectrum and the QWE polariton emission was observed as a shoulder on the high-energy side of the free QWE transition. In addition, two transitions at the low energy side of the free QWE photoluminescence were present in the microstructured samples, which were related to etching induced states.

Elastic scattering of exciton polaritons by neutral impurities.

A model based on the elastic scattering of exciton polaritons from residual neutral impurities is proposed to account for the line shape of the exciton-polariton photoluminescence emission in GaAs at low temperatures. The good agreement obtained with experimental spectra emphasizes the importance of impurity scattering on exciton-polariton transport for modes in the vicinity of the exciton energy. This model is applicable to any solid possessing dipole-active excitons.

Anisotropy of Exciton Polaritons and Polariton‐Phonon Interaction in 2H‐PbI2 Crystals. II. Anisotropy of the Photoluminescence of 2H‐PbI2

AbstractA detailed investigation of the anisotropy of the photoluminescence spectra of 2H–PbI2 as a function of the orientation of the electrical and propagation vectors of the emitted light is reported. The results are analysed in terms of exciton polariton emission and polaron mass anisotropy.