Generating indistinguishable photons from a quantum dot in a noisy environment

Single photons from semiconductor quantum dots are promising resources for linear optical quantum computing, or, when coupled to spin states, quantum repeaters. To realize such schemes, the photons must exhibit a high degree of indistinguishability. However, the solid-state environment presents inherent obstacles for this requirement as intrinsic semiconductor fluctuations can destroy the photon indistinguishability. Here, we demonstrate that resonant excitation of a quantum dot with a narrow-band laser generates near transform limited power spectra and indistinguishable photons from a single quantum dot in an environment with many charge-fluctuating traps. The specificity of the resonant excitation suppresses the excited state population in the quantum dot when it is detuned due to spectral fluctuations. The dynamics of this process lead to flickering of the emission over long time scales (>5 μs) and reduces the time-averaged count rates. Nevertheless, in spite of significant spectral fluctuations, high visibility two-photon interference can be achieved. This approach is useful for quantum dots with nearby surface states in processed photonic structures and quantum emitters in emerging platforms, such as two-dimensional semiconductors

Bismuth incorporation and the role of ordering in GaAsBi/GaAs structures

The structure and composition of single GaAsBi/GaAs epilayers grown by molecular beam epitaxy were investigated by optical and transmission electron microscopy techniques. Firstly, the GaAsBi layers exhibit two distinct regions and a varying Bi composition profile in the growth direction. In the lower (25 nm) region, the Bi content decays exponentially from an initial maximum value, while the upper region comprises an almost constant Bi content until the end of the layer. Secondly, despite the relatively low Bi content, CuPtB-type ordering was observed both in electron diffraction patterns and in fast Fourier transform reconstructions from high-resolution transmission electron microscopy images. The estimation of the long-range ordering parameter and the development of ordering maps by using geometrical phase algorithms indicate a direct connection between the solubility of Bi and the amount of ordering. The occurrence of both phase separation and atomic ordering has a significant effect on the optical properties of these layers

Demonstration of InAsBi photoresponse beyond 3.5 μm

An Indium Arsenide Bismide photodiode has been grown, fabricated, and characterized to evaluate its performance in the Mid Wave Infrared region of the spectrum. Spectral response from the diode has been obtained up to a diode temperature of 225 K. At this temperature, the diode has a cut off wavelength of 3.95 μm, compared to 3.41 μm in a reference Indium Arsenide diode, indicating that Bismuth has been incorporated to reduce the band gap of Indium Arsenide by 75 meV. Similar band gap reduction was deduced from the cut off wavelength comparison at 77 K. From the dark current data, shunt resistance values of 8 and 39 Ω at temperatures of 77 and 290 K, respectively, were obtained in our photodiode

Effects of rapid thermal annealing on GaAs 1-x

The effects of rapid thermal annealing on the optical and structural properties of GaAs1-xBix alloys for x ranging from 0.022 to 0.065 were investigated. At room temperature, the annealed GaAs1-xBix showed modest improvement (∼3 times) in photoluminescence (PL) while the PL peak wavelength remained relatively unchanged. It was found that bismuth related defects are not easily removed by annealing and the PL improvement may be dominated by the reduction of other types of defects including arsenic and gallium related defects. Also, the optimum annealing temperature is Bi composition dependent. For samples with x < 0.048, the optimum annealing temperature is 700 °C but reduces to 600 °C for higher compositions

Modelling of bismuth segregation in InAsBi/InAs superlattices: Determination of the exchange energies

InAsBi dilute alloys are potential new candidates for the improvement of infrared optoelectronic devices such as photodetectors or lasers. In this work, InAsBi/InAs superlattices (SLs)with Bi contents ranging between 1 and 3% were grown by molecular beam epitaxy with different Bi fluxes and growth temperatures to analyze Bi segregation by cross sectional transmission electron microscopy techniques. Bi segregation profiles have been described layer-by-layer using a three-layer fluid exchange mechanism, extracting the values of the As/Bi exchange energies (E 1 , 1.26 ± 0.01 eV and E 2 , 1.36 ± 0.02 eV). A relationship to calculate the activation energies for exchange from the binding energies in III–V alloys is proposed, which would allow predicting them for other hitherto unknown compounds

Design and characterization of high optical quality InGaAs/GaAs/AlGaAs-based polariton microcavities

The presence of dislocations arising from strain relaxation strongly affects polaritons through their photonic component and ultimately limits experiments involving polariton propagation. In this work, we investigate the range of growth parameters to achieve high optical quality GaAs/AlxGa1−xAs-based microcavities containing strained InxGa1−xAs quantum wells and using differential interference contrast (Nomarski) microscopy deduce a design rule for homogeneous versus disordered structures. We illustrate the effect of disorder by contrasting observations of polariton condensates in relaxed and unrelaxed microcavities. In our optimized device, we generate a polariton condensate and deduce a lifetime for the interacting polariton fluid of 39 ± 2 ps

Photoluminescence investigation of high quality GaAs1−xBix on GaAs

Photoluminescence (PL) of GaAs0.97Bi0.03 alloy was measured over a wide range of temperatures and excitation powers. Room temperature PL with peak wavelength of 1038 nm and full-width-half-maximum of 75 meV was observed which is relatively low for this composition. The improved quality is believed due to reduced alloy fluctuations by growing at relatively high temperature. The temperature dependence of PL peak energy indicated significant exciton localization at low temperatures. Furthermore, the band gap temperature dependence was found to be weaker than GaAs. An analysis of dominant carrier recombination mechanism(s) was also carried out indicating that radiative recombination is dominant at low temperature

The effect of Bi composition to the optical quality of GaAs 1−x

GaAs1−xBix alloys grown by molecular beam epitaxy for x up to 0.06 were studied by photoluminescence (PL). The results indicate that dilute fractions of bismuth (Bi) with x < 0.025 improve the material quality of this low temperature growth alloys by reducing the density of gallium (Ga) and/or arsenic related defects. The crystal quality starts to degrade at higher Bi concentration probably due to significant amount of Bi-related defects, BiGa. However, the room temperature PL intensity continues to increase with Bi content for the range studied due to greater band-gap offset between GaAs and GaAs1−xBix. Analysis carried out shows no correlation between localization effects and the room temperature PL enhancement

Optical and spin properties of localized and free excitons in GaBi ₓAs₁-ₓ /GaAs multiple quantum wells

Raman spectroscopy and magneto-photoluminescence measurements under high magnetic fields were used to investigate the optical and spin properties of GaBiAs/GaAs multiple quantum wells (MQWs). An anomalous negative diamagnetic energy shift was observed at higher temperatures and higher laser intensities, which was associated to a sign inversion of hole effective mass in these structures. In addition, an enhancement of the polarization degree with decreasing of laser intensity was observed (experimental condition where the emission is dominated by localized excitons). This effect was explained by changes of spin relaxation and exciton recombination times due to exciton localization by disorder

GaSbBi alloys and heterostructures: fabrication and properties

International audienceDilute bismuth (Bi) III-V alloys have recently attracted great attention, due to their properties of band-gap reduction and spin-orbit splitting. The incorporation of Bi into antimonide based III-V semiconductors is very attractive for the development of new optoelectronic devices working in the mid-infrared range (2-5 µm). However, due to its large size, Bi does not readily incorporate into III-V alloys and the epitaxy of III-V dilute bismides is thus very challenging. This book chapter presents the most recent developments in the epitaxy and characterization of GaSbBi alloys and heterostructures