Electronic structure and carrier dynamics in InAs/InP double-cap quantum dots

International audienceThe carrier dynamics in InAs double-cap quantum dots DC-QDs grown on InP113B are investigated. The shape of these QDs can be controlled during the growth, yielding an emission wavelength of the system of about 1.55 m at room temperature. The DC-QD dynamics is studied by time-resolved photoluminescence experiments at low temperature for various excitation densities. A simplified dynamic model is developed, yielding results consistent with experimental data. This analysis yields the determination of the Auger coefficients and the intradot relaxation time in this system

Carrier relaxation dynamics in InAs/InP quantum dots

International audienceThe electronic properties of InAs/InP(113)B double-cap quantum dots (QDs) emitting around 1.55 μm are investigated. The carrier dynamics in QDs is studied by non-resonant timeresolved photoluminescence (tr-PL) experiments. This analysis reveals the QD electronic structure and the transient filling of the confined QD levels. Under low excitation densities, the spontaneous exciton lifetime is estimated and compared to previous time-resolved resonant and non-resonant experiments. Under high excitation density, a direct Auger recombination effect is identified. The temperature analysis enables us to distinguish Auger and phonon-assisted relaxation processes

InAs quantum wires on InP substrate for VCSEL applications

International audienceQuantum dash based vertical cavity surface emitting lasers (VCSEL) on InP substrate are presented. Single and close stacking layers were successfully grown with molecular beam epitaxy. Optimized quantum dash layers exhibit a strong polarized 1.55 µm photoluminescence along the [1-10] crystallographic axis. Continuous wave laser emission is demonstrated at room temperature for the first time on a quantum dash VCSEL structure on InP susbtrate. The quantum dash VCSEL laser polarization appears stable on the whole sample and with excitation, no switching is observed. Its polarization is mainly oriented along [1-10], an extinction coefficient of 30 dB is measured. Those preliminary results demonstrate the interests of quantum dashes in the realization of controlled and stable polarization VCSEL device

Growth of quantum wires for long-wavelength VCSEL with a polarized laser emission

International audienceWe report continuous-wave operation at room temperature for a 1.55-µm VCSEL where the active region is made up of quantum-well. Now, self-organized quantum wires grown on InP substrate is used to obtain polarized laser emission

Si wafer bonded of a-Si/a-SiNx distributed Bragg reflectors for 1.55-µm wavelength vertical cavity surface emitting lasers

International audienceAmorphous silicon (a-Si) and amorphous silicon nitride (a-SiNx) layers deposited by magnetron sputtering have been analyzed in order to determine their optical and surface properties. A large value of ~1.9 of index difference is found between these materials. Distributed Bragg reflectors (DBR) based on these dielectric materials quarter wave layers have been studied by optical measurements and confronted to theoretical calculations based on the transfer matrix method. A good agreement has been obtained between the experimental and expected reflectivity. A maximum reflectivity of 99.5% at 1.55 µm and a large spectral bandwidth of 800 nm are reached with only four and a half periods of a-Si/a-SiNx. No variation of the DBR reflectivity has been observed with the time nor when annealed above 240°C and stored during few months. This result allows to use this DBR in a metallic bonding process to realize a vertical cavity surface emitting laser (VCSEL) with two dielectric a-Si/a-SiNx DBR. This bonding method using AuIn2 as the bonding medium and Si substrate can be performed at a low temperature of 240°C without damaging the optical properties of the microcavity. The active region used for this VCSEL is based on lattice-matched InGaAs/InGaAsP quantum wells and a laser emission has been obtained at room-temperature on an optically pumped device

Self-assembled InAs quantum dots grown on InP (3 1 1)B substrates: Role of buffer layer and amount of InAs deposited

International audienceThe formation of InAs quantum dots by Stransky–Krastanow method on (3 1 1)B InP substrates has been studied. On Al0.48In0.52As alloy lattice matched on InP, large changes of the quantum dot structural characteristics have been observed as a function of the amount of InAs deposited and of the arsenic pressure during the InAs quantum dot formation. Small quantum dots (minimum diameter=20 nm) in very high density (1.3×1011 quantum dots per cm2) have been achieved in optimized growth conditions. These results are interpreted from the strong strain field interaction through the substrate at high density and from the InAs surface energy evolutions with the Arsenic pressure. The effect on quantum dot characteristics of the arsenic pressure during the growth of Al0.48In0.52As buffer layers has also been investigated. Despite the importance of this parameter on the Al0.48In0.52As clustering, weak changes have been observed

Theoretical study of highly strained InAs material from first-principles modelling: application to an ideal QD

International audienceWe study the properties of highly strained InAs material calculated from first principles modeling using ABINIT packages. We first simulate the characteristic of bulk InAs crystal and compare them with both experimental and density functional theory (DFT) results. Secondly, we focus our attention on the strain effects on InAs crystal with a gradual strain reaching progressively the lattice matched parameters of InP, GaAs and GaP substrates. The final part is dedicated to the study of a hypothetic spherical InAs/GaP quantum dot. The effect of hydrostatic deformations for both InAs Zinc-Blende phase and InAs RockSalt phase is discussed

Characterization of InAs quantum wires on (001) InP: toward the realization of VCSEL structures with a stabilized polarization

International audienceVertical cavity surface emitting lasers (VCSELs) operating at 1.55-µm are of great interests in optical telecommunication applications. Their circular, spectral and spatial single mode laser beam is essential points for an efficient fiber coupling and high frequency modulation. Moreover, their low-cost production and the possibility to test each laser directly on the wafer represent great advantages for production applications. In contrast with edge emitting lasers, VCSEL present an important polarization instability, which may increase the bit error rate in data transmission. Different solutions have been proposed for controlling the polarization, from patterning the output mirror or by using a birefringent material on top of the mirror, which do complicate the device technology. In this contribution, we propose to use a gain material presenting an important polarization anisotropy like quantum wires in order to fix the polarization of the emitting VCSEL

Long-wavelength Vertical-Cavity Surface-Emitting Laser using an electro-optic index modulator with 10-nm tuning range

International audienceWe demonstrate an original approach to achieving a tunable 1.55-µm vertical-cavity surface-emitting laser. The tunability is based on an electro-optic index modulator using nano-sized droplets of liquid crystal as a phase layer. Such an approach can produce a robust and a low-cost device. A 10-nm tuning range with less than 170V applied voltage has been demonstrated. The device is formed by a conventional InP-based active region with an epitaxial and a dielectric Bragg mirror. This optically pumped device exhibits an excellent side-mode suppression ratio of higher than 20-dB over the whole spectral range

1.55-µm optically pumped tunable VCSEL based on a nano-polymer dispersive liquid crystal phase modulator

International audienceWe present a new approach to achieve tunability on a 1.55 μm vertical cavity surface emitting laser (VCSEL). Tunability is achieved thanks to an electro-optic index modulator. This electro-optic material consists in a n-PDLC phase layer introduced inside the VCSEL cavity. N-PDLC comprises nematic liquid crystal dispersed in a polymer material. This first VCSEL exhibits a 10 nm tuning range and an excellent side-mode suppression ratio higher than 20 dB over the whole spectral range. The device is formed by a conventional InP-based active region with an epitaxial and a dielectric Bragg mirror. The n-PDLC layer length, close to 6 μm, is in agreement with a tunable laser emission without mode-hopping. Another decisive advantage, compared to mechanical solutions, is the tuning response time which is close to a few 10 μs to scan the full spectral range, making this device appropriate for some access network functions. Voltage values are the main limiting factor, 170 Volts have been required to obtain 10 nm tunability, but material engineering is in progress to improve this point. We presented a first version of the device optically pumped, the next version will be electrically pumped as required for access network applications targeted here