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Exceptional points (EPs), singularities of non-Hermitian physics where complex spectral resonances degenerate, are one of the most exotic features of nonequilibrium open systems with unique properties. For instance, the emission rate of quantum emitters placed near resonators with EPs is enhanced (compared to the free-space emission rate) by a factor that scales quadratically with the resonance quality factor. Here, we verify the theory of spontaneous emission at EPs by measuring photoluminescence from photonic-crystal slabs that are embedded with a high-quantum-yield active material. While our experimental results verify the theoretically predicted enhancement, they also highlight the practical limitations on the enhancement due to material loss. Our designed structures can be used in applications that require enhanced and controlled emission, such as quantum sensing and imaging. Published version This work was partly funded by the French National Research Agency (ANR) under the Project POPEYE (Project No. ANR-17-CE24-0020) and the IDEXLYON from Universite de Lyon, Scientific Breakthrough project TORE within the Programme Investissements d Avenir (Project No. ANR-19-IDEX-0005) . It is also supported by the Auvergne-Rhne-Alpes region in the framework of PAI2020 and the Vingroup Innovation Foundation (VINIF) annual research grant program under Project No. VINIF.2021.DA00169. Q. X. gratefully acknowledges the funding support from National Natural Science Foundation of China (Grant No. 12020101003) and a Tsinghua University start-up grant.

We present in this paper the mechanical analysis of tunable InP-based Fabry-Perot filters. These filters are composed by a top and a bottom InP/air Bragg mirrors with a central air microcavity. The tunability is achieved by changing electrostatically the cavity thickness. We have developed a theoretical model using finite elements analysis (FEA) calculation method, which permits to evaluate the mechanical deformation of the central cavity. This model considers the electrostatic force between the two freestanding layers delimiting the central cavity. Using this model, we have analyzed the tuning performance of two kinds of device: a bridge structure and a square membrane. We have evaluated the influence on the mechanical performances of the involuntary underetching of the clamped ends at the freestanding layers extremities. The theoretical results have been compared to experimental ones obtained by optical reflectivity measurements.

We report on the photoluminescence characterization of a metalorganic vapour phase epitaxy grown InP/InAlAs/InP structure. The energy band alignment of the InAlAs/InP interface is of type II. The PL arising from the first grown interface (InAlAs grown on InP) is clearly seen at 1.2 eV. The localization was possible by scanning the laser beam on a angle-bevelled sample whose bevel crosses all the layers of the InP/InAlAs/InP structure. For the second interface, called the inverse interface (InP grown on InAlAs), a different PL behaviour is observed. The energy of the observed PL peak is 1.3 eV. It is very sensitive to the excitation power. From this behaviour, the Auger depth profiling measurements and the wedge transmission electron microscopy performed on this sample we conclude that this recombination does not originate from a type II interface band structure but from an InAs x P 1- x layer located at the inverse interface. This intermediate layer originates from the higher incorporation coefficient of As compared to that of P.

A characterization study of GaAs layers grown by metal-organic chemical vapour deposition (MOCVD) on silicon substrates is presented, based on high resolution transmission electron microscopy, secondary ion mass spectroscopy, admittance technique measurements (current-voltage, capacitance-voltage, capacitance and photocapacitance spectroscopy, deep level transient spectroscopy (DLTS) and photoluminescence (PL) spectroscopy in the near band gap and near infrared region). We have analysed the initial stage of growth and the influence of growth parameters as GaAs/AlAs superlattices (SLs) at different distances from the GaAsSi heterointerface in the buffer layer or post-growth thermal annealing or selective epitaxy on the reduction of dislocation density, on the silicon distribution, on the deep defect levels and on the coplanar tensile strain in the active layer. This study shows an improvement of the material quality in the dislocation density decrease due to GaAs/AlAs SLs grown directly on the initial prelayer, or post-growth annealing or selective epitaxy. DLTS measurements reveal deep electron traps in the range 0.5–0.7 eV below the CB induced by dislocations due to the heteroepitaxy. For the first time we observe deep hole centres in the range 0.4–0.5 eV above the top of the valence band, which could be involved in the reduction of the minority carrier lifetime. We discuss their origins due to silicon incorporation in the GaAs layer on the basis of capacitance and photoluminescence experiments. PL shows the increase of strain with post-growth annealing. Finally the improvement in the quality of the layers is pointed out on the basis of double heterostructure (GaAlAs/ GaAs/GaAlAs) characteristics.

An adiabatic taper is proposed to couple light from a photonic crystal waveguide to a coupled-cavity waveguide. A Scanning Near-Field Optical Microscopy study is realized on these structures. This study permits to identify and to evaluate accurately the losses in the coupled-cavity waveguide.

The epitaxial growth and characterization of InAs surface quantum wells grown on InP by molecular beam epitaxy (MBE) are discussed. The structural properties of the InAs layers are described. Photoluminescence results are presented. This system shows practically no coupling between the confined states in the InAs quantum well and the InAs surface states. >

The key performances of optical filters requested by optical communications for wavelength-division multiplexing (WDM) systems are: (i) a high wavelength selectivity, enabling the selection of neighboring channels 1.6 nm apart with a crosstalk ratio of 20 dB, (ii) a continuous wavelength tuning range of about 30 nm around 1.55 /spl mu/m, with no degradation of the selectivity. We demonstrate the design and the fabrication of a vertical micromachined InP-air gap based Fabry-Perot filter, continuously tunable via electrostatic micromechanical actuation of the cavity air gap, which meets the WDM system requirements.

High-quality fully strained ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ layers with 0%x22% grown on Si(100) by rapid thermal chemical vapor deposition have been analyzed by photoluminescence spectroscopy. We report a well-resolved near-band-gap excitonic transition observed in SiGe layers. These transitions make it possible to determine directly the fundamental band gap of such strained ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ alloys. The results show that high surface recombination in very thin films prevents the observation of radiative recombination, while demonstrating the striking effectiveness of a Si epitaxial capping layer in eliminating surface recombination.

At a low MBE growth temperature (400°C), an anisotropic composition modulation has been observed by Transmission Electron Microscopy (TEM) on AIlnAs layers. Optical measurements have been performed on these samples and compared with classical AllnAs grown at 530°C. We show the clustering “organization” on the low temperature layers and we propose some hypothesis to explain the composition modulation effects on the AlInAs optical properties.

We give an unambiguous identification of the single acceptor level (Fe3+/Fe2+) related to iron in Ga0.47In0.53As and a coherent description of its electrical and optical properties using photoluminescence, thermal and optical capacitance spectroscopies. Investigated layers are either Fe doped or undoped and grown on semi insulating Fe doped InP or n+ substrates by LPE or MBE methods. The internal photoluminescence transition of Fe2+ (5T2-5E) is detected at 0.35eV in the ternary for the first time. Deep level transient spectroscopy measurements show one deep level at Ec-0.34eV which we identify as being caused by the Fe3+/Fe2+ acceptor level. This is confirmed by the o (hv) spectrum of the photoionization cross-section which shows a very well marked resonance peak at 0.34eV due to the transition to the 5T2, excited state. Finally, we discuss the validity of the internal referred binding energy model to predict the band discontinuity in the InP/GaInAs system using the Fe3+/Fe2+ energy level position in the two materials.