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We address the radiative emission of individual germanium extrinsic centers in ${\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}$ epilayers grown on germanium substrates. Microphotoluminescence experiments demonstrate the capability of high temperature emission (70 K) and complex exciton configurations (neutral exciton $X$ and biexciton $XX$, positive ${X}^{+}$ and negative ${X}^{\ensuremath{-}}$ charged excitons) of these quantum emitters. Finally, we investigate the renormalization of each energy level showing a large and systematic change of the binding energy of $XX$ and ${X}^{+}$ from positive to negative values (from $\ensuremath{\sim}+5$ meV up to $\ensuremath{\sim}\ensuremath{-}7$ meV covering $\ensuremath{\sim}70$ meV of the emission energy) with increasing quantum confinement. These light emitters, grown on a silicon substrate, may exhibit energy-degenerate $X$ and $XX$ energy levels. Furthermore, they emit at the highest detection efficiency window of Si-based single-photon detectors. These features render them a promising device platform for the generation of entangled photons in the time-reordering scheme.

Effective monolithic integration strategies for high quality quantum III-V nanostructure fabrication on Si will be introduced. The methodologies presented range from ultrathin planar Ge virtual substrates for the integration of single photon emitters with high temperature stability to advanced three-dimensional Ge growths strategies.

Vertically aligned InAs/GaAs quantum dot structures were investigated. They were grown by atomic layer molecular beam epitaxy, with 10 layers and wedged spacer thickness d varying between 7.7 and 12.5 nm at steps of 0.2 nm. The effects of electronic coupling on the fundamental transition energy and decay dynamics were studied by time-resolved and continuous-wave photoluminescence (PL). The energy of the PL peak position decreases with increasing d, while the corresponding lifetime increases with d. This is attributed to the interplay of the electronic delocalization along the column and the Coulomb interaction between electrons and holes. Furthermore, a bell-shaped behaviour of the PL lifetime as a function of emission energy was observed inside the inhomogeneously broadened PL band.

The nature of hot electron electroluminescence (EL) in AlGaN/GaN high electron mobility transistors is studied and attributed to Bremsstrahlung. The spectral distribution has been corrected, for the first time, for interference effects due to the multilayered device structure, and this was shown to be crucial for the correct interpretation of the data, avoiding artefacts in the spectrum and misinterpretation of the results. An analytical expression for the spectral distribution of emitted light is derived assuming Bremsstrahlung as the only origin and compared to the simplified exponential model for the high energy tail commonly used for electron temperature extraction: the electron temperature obtained results about 20% lower compared to the approximated exponential model. Comparison of EL intensity for devices from different wafers illustrated the dependence of EL intensity on the material quality. The polarization of electroluminescence also confirms Bremsstrahlung as the dominant origin of the light emitted, ruling out other possible main mechanisms.

Demanding applications such as video streaming, social networking, or web search relay on a large network of data centres, interconnected through optical links. The ever-growing data rates and power consumption inside these data centres are pushing copper links close to their fundamental limits. Optical interconnects are being extensively studied with the purpose of solving these limitations. Among the different possible technology platforms, silicon photonics, due to its compatibility with the CMOS platform, has become one of the preferred solutions for the development of the future generation photonic interconnects. However, the on-chip integration of all photonic and optoelectronic building blocks (sources, modulators and detectors…) is very complex and is not cost-effective due to the various materials involved (Ge for detection, doped Si for modulators and III-V for lasing). Carbon nanotubes (CNTs) are nanomaterials of great interest in photonics thanks to their fundamental optical properties, including near-IR room-temperature foto- and electro- luminescence, Stark effect, Kerr effect and absorption. In consequence, CNTs have the ability to emit, modulate and detect light in the telecommunications wavelength range. Furthermore, they are being extensively developed for new nano-electronics applications. In this work, we propose to use CNTs as active material integrated into silicon photonics for the development of all optoelectronic devices. Here, we report on the development of new integration schemes to couple the light emission from CNTs into optical resonators implemented on the silicon-on-insulator and silicon-nitride-on-insulator platforms. A theoretical and experimental analysis of the light interaction of CNTs with micro-ring resonators based on strip and slot waveguides and slot photonic crystal heterostructure cavities were carried out.

International audience; Hybrid structures are needed to fully exploit the great advantages of Si photonics and several approaches have been addressed where Si devices are bonded to different materials and nanostructures. Here we study the use of semiconductor carbon nanotubes for emission in the 1300 nm wavelength range to functionalize Si photonic structures in view of optoelectronic applications. The Si micro-rings are fully characterized by near field forward resonant scattering with 100 nm resolution. We show that both TE and TM modes can be addressed on the top of the micro-rings in a vectorial imaging of the in-plane polarization components. We coupled the Si micro-resonators with selected carbon nanotubes for high photoluminescence emission. Coupling nanotubes with the evanescent tails in air of the electric field localized in the photonic modes of the micro-resonators is demonstrated by sharp resonances over imposed to the nanotube emission bands. By mapping the Si and the nanotube emission we demonstrate that strong enhancement of the nanotube photoluminescence can be achieved both in the photonic modes of micro-disks and slot micro-rings, whenever the spatial overlap between nano-emitters and photonic modes is fulfilled.

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International audience; Single-wall carbon nanotubes (SWNTs) are known for their exceptional physical properties ranging from mechanics to electronics and optics. These properties are expected to give rise to innovative applications, especially when nanotubes are incorporated in new functional devices. However, the conception of an effective SWNT-based electronic or optoelectronic technology faces three main concerns: the extraction of semiconducting SWNTs having the desired optoelectronic characteristics from the as-synthetized poly-disperse mixture; the deposition of high nanotube concentrations at desired areas to increases transport and optical performances and the alignment of nanotubes on the substrate. Using an effective polymer-assisted sorting approach, we obtain highly-selective separation of semiconducting SWNTs that can be coupled with optoelectronic silicon-based devices operating at the telecom wavelength of 1.5 µm. Our modified evaporative self-assembly approach can deposit concentrated SWNT networks with configurations varying from random to highly-oriented assembly. In the latter case, the obtained orientation is particularly favorable for device fabrication and operation. Several configurations enabling photo-detection and electroluminescence at the chip level are currently under investigation and the latest results will be presented.

International audience; Hybrid structures are needed to fully exploit the great advantages of Si photonics and different approaches have been addressed where Si devices are bonded to different materials and nanostructures. Here we experimentally study the use of semiconductor carbon nanotubes for emission in the 1300 nm wavelength range to functionalize Si photonic structures in view of optoelectronic applications. The Si microrings are fully characterized by near field forward resonant scattering with 100 nm resolution. We show that both TE and TM modes can be addressed on the top of the microrings in a vectorial imaging of the in-plane polarization components. We coupled the Si microresonators with selected carbon nanotubes for high photoluminescence emission. Coupling of the nanotubes with the evanescent tails in air of the electric field localized in the photonic modes of the microresonators is demonstrated by sharp resonances overimposed to the nanotube emission bands. By mapping the Si and the nanotubes emission we demonstrate that strong enhancement of the nanotubes photoluminescence can be achieved both in the photonic modes of microdisks and slot microrings, whenever the spatial overlap between nanoemitters and photonic modes is fulfilled.

We present a detailed experimental study of the line broadening of the different excitonic complexes inside single GaAs/AlGaAs quantum dots. The investigated nanostructures are self assembled quantum dots (QDs), strain free nanocrystals grown by Modified Droplet Epitaxy technique. They show a typical PL spectrum with a triplet structure and by time correlated spectroscopy each contribution can be unambiguously assigned to neutral exciton, biexciton and trion. By high resolution spectroscopy, we have studied the line broadening for several single GaAs/AlGaAs QDs. The measured linewidth is found to vary between several tens to few hundreds of meV and we attribute this to spectral diffusion. The striking feature of the PL spectrum is that the trion and the biexciton line are always sharper with respect to the neutral exciton (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this contribution we report the results of polarization resolved, high resolution photoluminescence spectroscopy of single lattice-matched, GaAs/Al0:3Ga0:7As quantum dots. The investigated samples are self assembled, strain free nanocrystals grown by Modifed Droplet Epitaxy technique. The lack of strain reflects in a nominal lack of piezoelectric field making such nanostructures potentially highly symmetric and suitable systems as polarization entangled photon sources. The high resolution, polarization resolved photoluminescence from isolated emitters present a clear linearlypolarized fine spectral splitting between the neutral exciton and biexciton lines while charged complexes are completely degenerate. By measuring the fine structure splitting and the line broadening of the excitonic photoluminescence we get new insights on the overlap of the opposite polarized lines (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

International audience; Silicon photonics, due to its compatibility with the CMOS platform and unprecedented integration capability, has become the preferred solution for the implementation of next generation optical interconnects. However, current Si photonics require on-chip integration of several materials, including III-V for lasing, doped silicon for modulation and Ge for detection. The very different requirements of these materials result in complex fabrication processes that offset the cost-effectiveness of the Si photonics approach. We are developing an alternative route towards the integration of optoelectronic devices in Si photonic, relying on the use of single wall carbon nanotubes (SWNTs). SWNTs can be considered as a Si compatible material able to emit, modulate and detect near-infrared light. Hence, they hold a unique potential to implement all active devices in the Si photonics platform. In addition, solution processed SWNTs can be integrated on Si using spin-coating techniques, obviating the need of complex epitaxial growth or chip bonding approaches. Here, we report on our recent progress in the coupling of SWNTs light emission into optical resonators implemented on the silicon-on-insulator (SOI) platform.

International audience; Hybrid systems based on carbon nanotubes emitting in the telecom wavelength range and Si-photonic platforms are promising candidates for developing integrated photonic circuits. Here, we consider semiconducting single walled carbon nanotubes (s-SWNTs) emitting around 1300 nm or 1550 nm wavelength. The nanotubes are deposited on quartz substrate for mapping their photoluminescence in hyperspectral near-field microscopy. This method allows for a sub-wavelength resolution in detecting the spatial distribution of the emission of single s-SWNTs at room temperature. Optical signature delocalized over several micrometers is observed, thus denoting the high quality of the produced carbon nanotubes on a wide range of tube diameters. Noteworthy, the presence of both nanotube bundles and distinct s-SWNT chiralities is uncovered.

We present both experimental and theoretical results which outline our development of the molecular beam epitaxy of GaN microcavities on (111) silicon. In particular we show that although in this material system the strong-light matter coupling regime can be observed at 300 K even with relatively low quality factor structures (Q = 60) in reflectivity measurements, it is necessary to increase the Q -factor by at least a factor of two to observe strong coupling in the emission. For an optimized microcavity structure (Q = 160), polaritonic emission is observed at 300 K, with the origin of the broadened luminescence features confirmed by co-incident reflectivity measurements. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The multiexciton properties of extrinsic centers from AlGaAs layers on Ge and Si substrates are addressed. The two photon cascade is found both in steady state and in time resolved experiments. Polarization analysis of the photoluminescence provides clearcut attribution to neutral biexciton complexes. Our findings demonstrate the prospect of exploiting extrinsic centers for generating entangled photon pairs on a Si based device. © 2013 AIP Publishing LLC.

International audience; A deep-subwavelength imaging of the optical-guided modes localized in silicon microring resonators, obtained with a polarization-sensitive Fano-imaging technique, is demonstrated. We merge together near-field scanning optical microscopy and resonant forward scattering spectroscopy, leading to near-field hyperspectral imaging without the need of embedded light emitters or evanescent light coupling into the microring. The combined analysis of the observed Fano-like spectral line shapes and of the near-field intensity spatial distributions, supported by accurate numerical calculations, gives a clear discrimination between the TE and the TM modes.

We study the multiexciton properties of GaAs quantum dots self aggregated on Si substrates. Sequential emission of two photons radiative cascade is observed both in continuous wave and in time resolved measurements. Polarization resolved measurements, with high spectral resolution, allow us to attribute the observed photon cascade to positively charged biexciton. Our results highlight the possibility of obtaining systems showing quantum correlations on a Si based device.

We show that the epitaxial growth of height-controlled GaAs quantum dots, leading to the reduction of the inhomogeneous emission bandwidth, produces individual nanostructures of peculiar morphology. Besides the height controlled quantum dots, we observe nanodisks formation. Exploiting time resolved and spatially resolved photoluminescence we establish the decoupling between quantum dots and nanodisks and demonstrate the high optical properties of the individual quantum dots, despite the processing steps needed for height control. © 2013 AIP Publishing LLC.

We describe a method for the direct epitaxial growth of a single photon emitter, based on GaAs quantum dots fabricated by droplet epitaxy, working at liquid nitrogen temperatures on Si substrates. The achievement of quantum photon statistics up to T=80 K is directly proved by antibunching in the second order correlation function as measured with a H anbury Brown and Twiss interferometer. © 2013 AIP Publishing LLC.

The integration of III-V nanostructures on silicon would allow to combine the high performance of III-V quantum photonic devices and of CMOS circuitry embedded on Si. In this work, we present the fabrication and characterization of single photon emission from high quality GaAs quantum dots (QDs) grown by droplet epitaxy (DE) [1] on Si through a thin Ge buffer layer deposited by Low Energy Plasma Enhanced Chemical Vapour Deposition (LEPECVD) [2]. In figure 1 a sketch of the sample is reported. The deposition of a thin Ge layer by LEPECVD allows for the reduction of threading dislocation density down to few 107 cm−2. DE is an intrinsically low thermal budget technique, being performed at temperatures between 200 and 350 °C. This makes DE perfectly suited for the implementation of growth procedures compliant with back-end integration of III-V nanostructures on CMOS. GaAs QDs with a density of few 108 cm−2 and a mean height of 8 nm are fabricated by DE inside a Al0.30Ga0.70As barrier. To improve the quality of the GaAs QDs, two annealing procedure with reduced thermal budget are performed. The first one in chamber right after the quantum dots deposition to desorb As excess, the second one in a rapid thermal annealing system in order to improve crystal quality. Bright and sharp emission lines are observed in a micro-photoluminescence experiment around 700 nm, with pure radiative excitonic lifetime and clear evidence of exciton-biexciton cascade [3]. The achievement of quantum photon statistics is directly proved by antibunching in the second order correlation function as measured with a Hanbury Brown and Twiss interferometer up to T=80 K (figure 2), thus making the single photon emitter working at liquid nitrogen temperature and compatible with present CMOS technology. The optical quality of the GaAs quantum dots grown on Si substrate is almost comparable with quantum dots directly grown on GaAs substrates, clearly demonstrating a new procedure for the integration of high efficient light emitters, based on III-V semiconductors, directly on Si substrates, and opening the route to wide applications to optoelectronics, photonics and quantum information technology. [1] N. Koguchi, K. Ishige, and S. Takahashi, Journal of Vacuum Science & Technology B 11, 787 (1993). [2] G. Isella, D. Chrastina, B. Roessner, T. Hackbarth, H.-J. Herzog, U. Koenig , H. von Kaenel , Solid-State Electronics 48, 1317 (2004). [3] L. Cavigli, S. Bietti, N. Accanto, S. Minari, M. Abbarchi, G. Isella, C. Frigeri, A. Vinattieri, M. Gurioli, and S. Sanguinetti, Applied Physics Letters 100, 231112 (2012).

One of the fundamental ingredients for quantum cryptography and quantum information applications is the fabrication of single and entangled photon emitters. Single photon emitter should produce exactly a single photon on demand, should work not only at cryogenic temperature and should be easy to produce and to integrate on existing electronic devices. In this work, we present the fabrication and characterization of single photon emission from high quality GaAs quantum dots (QDs) by droplet epitaxy (DE) and from impurity centers in AlGaAs layers grown on Si through a thin Ge buffer layer deposited by Low Energy Plasma Enhanced Chemical Vapour Deposition (LEPECVD). The deposition of a thin Ge layer by LEPECVD and subsequent annealing cycles allow for the reduction of threading dislocation density down to few 107 cm-2. DE is an intrinsically low thermal budget technique, being performed at temperatures between 200 and 350 °C. This makes DE perfectly suited for the implementation of growth procedures compliant with back-end integration of III-V nanostructures on CMOS. GaAs QDs with a density of few 108 cm-2 and a mean height of 8 nm are fabricated by DE inside a Al0.3Ga0.7As barrier. Bright and sharp emission lines are observed in a micro-photoluminescence experiment around 700 nm, with pure radiative excitonic lifetime and clear evidence of exciton-biexciton cascade. The achievement of quantum photon statistics is directly proved by antibunching in the second order correlation function as measured with a Hanbury Brown and Twiss interferometer up to T=80 K, thus making the single photon emitter working at liquid nitrogen temperature and compatible with present CMOS technology. The optical quality of the GaAs quantum dots grown on Si substrate is almost comparable with quantum dots directly grown on GaAs substrates. We also show that the epitaxial growth of thin layers of Al0.3Ga0.7As on GaAs buffer layers grown on Si and Ge substrates allows to obtain a single photon source by exploiting the strewn and unintentional contamination with defects of the Al0.3Ga0.7As. Very bright and sharp single photoluminescence lines are observed in confocal microscopy. These lines behave very much as single excitons in QDs, but their realization is by far much easier, since it does not require 3D nucleation or spatially selective doping. The photon antibunching is demonstrated by time resolved Hanbury Brown and Twiss measurements. In both cases (GaAs QDs by DE and impuritues in AlGaAs layer) it is clearly demonstrated a new procedure for the integration of high efficient light emitters, based on III-V semiconductors, directly on Si substrates, and opening the route to wide applications to optoelectronics, photonics and quantum information technology.

We have investigated in detail the dependence of the photoluminescence decay times in stacked quantum dot (QD) structures, showing that they strongly depend on the emission energy. We propose that the dispersion of the lifetimes has to be related to the presence of vertical disorder in the quantum dot column. Due to the disorder the energy distribution of the carrier extended states shrinks and localized states are created in the tails. This idea is supported by a theoretical model, which takes into account the presence of a vertical disorder along the QD columns. (C) 2003 American Institute of Physics.

We report on recombination kinetics, by means of time resolved photoluminescence technique, on GaN quantum discs embedded in strain free AlGaN nanocolumn. The emission of the 100 A QD shows a very long time decay (about 20 ns), denoting a small radiative rate; in contrast, fast decay time are observed in the case of 20 A disc (∼450 ps). At the same time a large blue shift of the PL band is found in the 100 A QD when increasing the power excitation while the PL of the 20 A QD does not show any energy shift. The whole phenomenology can be interpreted in terms of piezoelectric polarization fields inside the strained GaN QDs embedded in relaxed AlGaN nanocolumn (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present a study of the emission of a multi-layer stack of self-assembled GaN/AlN quantum dots grown on the a -plane of 6H-SiC. We look for signatures of the internal electric field in the power dependence of the time-integrated and time-resolved photoluminescence spectra. The lack of a dynamical red-shift reveals that internal electric fields are significantly reduced in these dots. A band on the low energy side of the emission is observed whose intensity quenches fast when increasing the temperature. The polarization selection rules of the emission are examined in order to determine the physical nature of this band. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on time-resolved photoluminescence (PL) experiments on ‘polarization-matched’ GaN/InAlGaN heterostructures, to get unique information on the recombination kinetics of nitride quantum wells (QWs) without the obscuring influence of polarization-induced internal fields. The samples have been grown by MBE choosing an In content of 14% and an Al content of 24% in order to compensate the internal fields. We have measured PL time decay as a function of several experimental parameters on a selected number of InAlGaN/GaN QWs. Careful analysis of time resolved spectra allows to isolate the intrinsic contribution from extrinsic bands. Very fast recombination times have been observed, demonstrating the enhancement of the exciton oscillator strength in these zero-field GaN based QWs, with recombination times down to about a hundred ps. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on the study of carrier dynamics and recombination by time resolved PL in GaN quantum discs embedded in Al0.16Ga0.84N nanocolumns, grown by MBE on AlN buffered Si (111) substrates. The emission band of GaN quantum discs and the Al0.16Ga0.84N nanocolumns are strongly overlapped and the standard analysis of PL decays is not useful to fully characterize the recombination kinetics. We make use of time resolved spectroscopy to clearly distinguish the different contributions to the PL spectra and therefore to obtain the intrinsic carrier time evolution in the quantum discs. We observe a dynamical red shift of the PL band together with a non exponential decay, very likely due to screening of the internal piezoelectric field provided by the photoinjected carriers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on triggered single photon emission from GaAs quantum dots, grown on Si substrates and obtained by means of fabrication protocols compatible with the monolithic integration on Si based microelectronics. Very bright and sharp individual exciton lines are resolved in the spectra and can be followed up to 150 K. The nature of quantum emitters of single photon pulses can be measured up to liquid nitrogen temperature by Hanbury Brown and Twiss interferometric correlations. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4726189]

The emission dynamics in GaAs/AlGaAs coupled ring-disk (CRD) quantum structures fabricated on silicon substrates is presented. The CRD structures are self-assembled via droplet epitaxy, a growth technique which, due to its low thermal budget, is compatible with the monolithic integration of III-V devices on Si based electronic circuits. Continuous wave, time resolved photoluminescence and theoretical calculations in the effective mass approximations are presented for the assessment of the electronic and carrier properties of the CRDs. The CRDs show a fast carrier dynamics which is expected to be suitable for ultrafast optical switching applications integrated on silicon.

The integration of III-V nanostructures on silicon would allow to combine the high performance of quantum photonic devices and of CMOS circuitry on Si. In this work, we present the first demonstration of single photon emission from high quality GaAs quantum dots (QDs) grown by droplet epitaxy on Si substrates using a thin Ge buffer layer deposited by Low Energy Plasma Enhanced Chemical Vapour Deposition (LEPECVD). Droplet epitaxy allows for the separate control of the QD size and density, and provides the possibility to fabricate different classes of quantum nanostructures with tailored wavefunctions and electronic levels. Droplet epitaxy is also an intrinsically low thermal budget growth, being performed at temperatures between 200 and 350 C. This makes droplet epitaxy perfectly suited for the realization of growth procedures compatible with back-end integration of III-V nanostructures on CMOS. The deposition of a thin Ge layer by LEPECVD allows for the reduction of threading dislocation density down to few 10^-7 cm . GaAs QDs with a density of few 10 cm and a mean height of 8 nm are fabricated by droplet epitaxy inside a Al0.30Ga0.70 As barrier. Two annealing procedure are performed, the first one in chamber right after the quantum dots growth to desorb As excess while the second one (performed in a rapid thermal annealing system) improves crystal quality. Bright and sharp emission lines are observed in a micro-photoluminescence experiment around 700 nm, with pure radiative excitonic lifetime and clear evidence of exciton-biexciton cascade. The achievement of quantum photon statistics is directly proved by antibunching in the second order correlation function as measured with a Hanbury Brown and Twiss interferometer up to T=80 K, thus making the single photon emitter working at liquid nitrogen temperature and compatible with present CMOS technology. The optical quality of the GaAs quantum dots grown on Si substrate is almost comparable with quantum dots directly grown on GaAs substrates, clearly demonstrating a new procedure for the integration of high efficient light emitters, based on III-V semiconductors, directly on Si substrates, and opening the route to wide applications to optoelectronics, photonics and quantum information technology.

Physical properties of nanostructures are strongly influenced by their dimensions and shapes, so only a precise control on the nanocrystals morphology can allow for the fine tuning of their electronic properties. The Droplet Epitaxy (DE)[1,2] is intrinsically a low thermal budget growth, being performed at temperatures between 200 and 350 °C and is a flexible growth method, based on the sequential supply of III-column and V-column elements, which permits the fabrication of a large variety of different structures such as quantum dots (QDs), quantum rings (QRs)[3,4] and concentric quantum double rings (CQDRs)[4]. In this presentation we show the possibility to tune GaAs QDs nanostructures to act as single quantum emitters on Si substrates. The integration of III-V nanostructures on silicon would open the possibility to pursue integration between high performance quantum photonic devices and quantum information technology devices based on CMOS circuitry on Si. Low thermal budget of droplet epitaxy technique is perfectly suited for the realization of growth procedures compatible with back-end integration of III-V nanostructures on CMOS [5]. The control of the growth kinetics allows the fabrication of quantum dot samples with an areal density down to few 108 cm-2. Bright and sharp emission lines are observed in a micro-photoluminescence experiment around 700 nm, with pure radiative excitonic lifetime and clear evidence of exciton-biexciton cascade. The achievement of quantum photon statistics is directly proved by antibunching in the second order correlation function as measured with a Hanbury Brown and Twiss interferometer up to T=80 K, thus making the single photon emitter working at liquid nitrogen temperature and compatible with present CMOS technology. Optical quality of the GaAs quantum dots grown on Si substrate is almost comparable with quantum dots directly grown on GaAs substrates, clearly demonstrating a new procedure for the integration of high efficient light emitters, based on III-V semiconductors, directly on Si substrates, and opening the route to wide applications to optoelectronics, photonics and quantum information technology.[1] N. Koguchi, S. Takahashi, T. Chikyow, J. Crystal Growth 111 (1991) 688. [2] N. Koguchi and K. Ishige, Jpn. J. Appl. Phys. 32 (1993) 2052-2058. [3] K. Watanabe, N. Koguchi and Y. Gotoh, Jpn. J. Appl. Phys. 39 (2000) L79. [4] T. Mano et al, Nano Letters 5, 3, 425-428 (2005). [5] S. Bietti, C. Somaschini, S. Sanguinetti, N. Koguchi, G. Isella, and D. Chrastina, Appl. Phys. Lett. 95, 241102 (2009) [6] Cavigli L., Abbarchi M., Bietti S., Somaschini C., Sanguinetti S., Koguchi N., Vinattieri A., et al. App. Phys. Lett., 98(10), 103104 (2011)

The integration of III-V nanostructures on silicon would open the possibility to pursue integration between high performance quantum photonic devices and quantum information technology devices based on CMOS circuitry on Si. In this work, we present the growth and optical characterization of high quality GaAs quantum dots (as single photon emitters) grown by droplet epitaxy on Si substrates through the deposition of a thin Ge layer. Droplet epitaxy [1] is intrinsically a low thermal budget growth, being performed at temperatures between 200 and 350 °C. This makes droplet epitaxy perfectly suited for the realization of growth procedures compatible with back-end integration of III-V nanostructures on CMOS [2]. The control of the growth kinetics allows the fabrication of quantum dot samples with an areal density down to few 108 cm-2. Bright and sharp emission lines are observed in a micro-photoluminescence experiment around 700 nm, with pure radiative excitonic lifetime and clear evidence of exciton-biexciton cascade. The achievement of quantum photon statistics is directly proved by antibunching in the second order correlation function as measured with a Hanbury Brown and Twiss interferometer up to T=80 K, thus making the single photon emitter working at liquid nitrogen temperature and compatible with present CMOS technology. Optical quality of the GaAs quantum dots grown on Si substrate is almost comparable with quantum dots directly grown on GaAs substrates, clearly demonstrating a new procedure for the integration of high efficient light emitters, based on III-V semiconductors, directly on Si substrates, and opening the route to wide applications to optoelectronics, photonics and quantum information technology. [1] N. Koguchi, S. Takahashi, T. Chikyow, J. Crystal Growth 111 (1991) 688. [2] S. Bietti, C. Somaschini, S. Sanguinetti, N. Koguchi, G. Isella, and D. Chrastina, Applied Physics Letters 95, 241102 (2009)

We present an experimental investigation of InxGa1−xN/GaN multiple quantum well structures, with well widths ranging between 10 and 40 A and an indium content 0.03 < x < 0.07. Given such values, both the electric built-in field and localization due to potential fluctuation affect the carrier dynamics. We will show that, by means of time-integrated, time-resolved photoluminescence spectra and cathodoluminescence experiments, different processes affecting the recombination dynamics can be evidenced. A comparison with theoretical simulations of the carrier dynamics provides a nice agreement with experiments. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on the nucleation of low density and defect-free GaAs quantum dots (QDs) on Ge substrates. The growth of III-V nanostructures was realized via droplet epitaxy technique. A detailed micro- and macro-photoluminescence analysis shows that the optical quality of the GaAs QDs is almost comparable with state-of-the-art QDs directly grown on GaAs substrates. Bright and sharp exciton and biexciton lines of individual QDs have been observed. This achievement opens the route to the realization of quantum optoelectronic devices on IV semiconductor substrates. © 2011 American Institute of Physics.

The integration of III-V nanostructured active layers on silicon could open interesting perspectives for implementation of high performance devices for optoelectronics, photonics and quantum information technology within CMOS circuits [1]. Nanostructures based on III-V semiconductor materials have better optical properties compared to Si, and their use has largely improved optoelectronic devices performances, such as semiconductor laser. Even more striking is the possibility to exploit quantum dots with three-dimensional quantum confinement and deltalike density of states for quantum devices such as single photon [2] or entangled photon pairs emitters [3]. In this presentation, we explore the growth and optical characterization of high quality and low density GaAs quantum dots grown by droplet epitaxy [4] on Ge substrates and the possibility to integrate the same nanostructures on Si through Ge virtual substrates [5]. The adoption of droplet epitaxy method is of utter importance for our target. Droplet epitaxy is intrinsically a low thermal budget growth, being performed at temperatures between 200 and 350 °C. This makes droplet epitaxy perfectly suited for the realization of growth procedures compatible with back-end integration of III-V nanostructures on CMOS emitters. The control of the growth kinetics permitted the fabrication of quantum dot samples with extremely low areal densities (down to few 108cm -2). Single quantum dot spectroscopic characterization has been performed, by means of a micro-photoluminescence apparatus, without the need of further sample processing. Optical quality of the GaAs quantum dots is almost comparable with quantum dots directly grown on GaAs substrates, clearly demonstrating with such achievement, a new procedure for the integration of high efficient light emitters, based on III- V semiconductors, directly on IV semiconductor substrates, and opening the route to wide applications to optoelectronics, photonics and quantum information technology. [1] S. Bietti, C. Somaschini, S. Sanguinetti, N. Koguchi, G. Isella, and D. Chrastina, Applied Physics Letters 95, 241102 (2009). [2] T. Kuroda, M. Abbarchi, T. Mano, K. Watanabe, M. Yamagiwa, K. Kuroda, K. Sakoda, G. Kido, N. Koguchi, C. Mastrandrea, L. Cavigli, M. Gurioli, Y. Ogawa, and F. Minami, , Applied Physics Express 1 042001(2008) [3] A. Dousse, J. Suffczynski, Alexios Beveratos, Olivier Krebs, Aristide Lemaıtre, Isabelle Sagnes, Jacqueline Bloch, Paul Voisin, and Pascale Senellart, Nature (London) 466, 217 (2010) [4] N. Koguchi, S. Takahashi, T. Chikyow, J. Crystal Growth 111 (1991) 688. [5] J. Osmond, G. Isella, D. Chrastina, R. Kaufmann, M. Acciarri, and H. von Kaenel, Applied Physics Letters 94, 201106 (2009).

Self-organized GaN/AlN stacked quantum dots (QDs) have been studied by means of cathodoluminescence (CL), near field scanning optical microscopy (NSOM), photoluminescence, mu-Raman, and transmission electron microscopy. Assignment of the optical emissions was made on the basis of the structural parameters, power-dependent optical studies and depth-resolved CL. Power-dependent studies allowed us to distinguish between quantum confined and buffer emissions. On increasing the power injection conditions, a QD-size-dependent blue shift due to the screening of the internal electric fields was found together with a trend to saturation observed in the high injection limit. The possible evidence of excited states has also been shown by power-dependent photoluminescence and CL. Different blue shifts in specimens with different numbers of stacked layers suggested possible different residual strain values as confirmed by mu-Raman studies. Depth-resolved CL investigations performed at constant power injection per unit volume allowed us to distinguish between QD layers with different nominal GaN coverages and a linear dependence of peak energy versus GaN monolayer number has also been found. Adding 1 ML of GaN resulted in an average shift of about 150 meV. The existence of QDs with different size distributions along the growth axis was also found. The observations were confirmed by NSOM spectroscopy.

We present the results of high resolution photoluminescence spectroscopy of single GaAs/AlGaAs quantum dots grown by droplet epitaxy technique. By measuring the line broadening and the linear polarization of the excitonic photoluminescence we get new insights on the role of extrinsic effects on the quantum dot symmetry. Taking advantage of the lack of strain in the GaAs/AlGaAs system we study the relationship between the geometrical elongation of the confining potential and the exciton fine structure splitting. © 2009 Elsevier B.V. All rights reserved.

The selective growth of InAs quantum dot chains self-ordered at mesoscopic distances on a rippled GaAs(001) substrate is obtained by tuning the direction of the As flux at high temperature and high As/In flux ratio. Microphotoluminescence experiments demonstrate that such isolated quantum dot chains show single quantum dot emission properties.