The room-temperature light emission of uncapped III-V semiconductor quantum dots is used to inves... more The room-temperature light emission of uncapped III-V semiconductor quantum dots is used to investigate the properties and evolution of the surface under exposure to a humid environment. Enhanced photoluminescence intensity resulting from exposure to polar molecules has already been reported; here we demonstrate that the external environment also has a relevant effect on the emission energy of quantum dots. Experimental results are interpreted on the basis of a model of the quantum system that takes into account the formation of oxide on pristine III-V surfaces and the presence of surface states. As a result of our study, we can clearly distinguish the effect of surface oxidation from that of surface state passivation on the emission of InAs surface quantum dots. This work sheds new light on the properties of semiconductor surface quantum dots as building blocks of novel and highly efficient sensing devices based on optical transduction.
New optical fiber based spectroscopic tools open the possibility to develop more robust and effic... more New optical fiber based spectroscopic tools open the possibility to develop more robust and efficient characterization experiments. Spectral filtering and light reflection have been used to produce compact and versatile fiber based optical cavities and sensors. Moreover, these technologies would be also suitable to study N-photon correlations, where high collection efficiency and frequency tunability is desirable. We demonstrated single photon emission of a single quantum dot emitting at 1300 nm, using a Fiber Bragg Grating for wavelength filtering and InGaAs Avalanche Photodiodes operated in Geiger mode for single photon detection. As we do not observe any significant fine structure splitting for the neutral exciton transition within our spectral resolution (46 μeV), metamorphic QD single photon emission studied with our all-fiber Hanbury Brown & Twiss interferometer could lead to a more efficient analysis of entangled photon sources at telecom wavelength. This all-optical fiber scheme opens the door to new first and second order interferometers to study photon indistinguishability, entangled photon and photon cross correlation in the more interesting telecom wavelengths. New emerging quantum optics technologies are mostly influenced by the possibility to design realistic proposals to implement and control quantum correlations between photons 1. Single photon and entangled photon emission has been demonstrated by different techniques and systems 2 , as for example by non-linear processes (parametric down conversion or four wave mixing) or by two level systems (atoms, molecules, Quantum Dots, single impurities or Nitrogen Vacancies in Diamond). However, an entangled photon source must fulfill several requirements for its use in quantum applications 3 : deterministic generation of entangled photons, high fidelity to the Bell state, high photon indistinguishability, and high efficiency. Although non-linear processes generate entangled photons at room temperature, two-level systems offer the opportunity to build a deterministic device, i.e., a system where entangled photons are emitted on demand by an external control (laser pulse or electrical signal). Furthermore, it is interesting to generate entangled photon emission compatible with optical fiber technologies, thus it is necessary to tune the optical emission to the second and third optical telecommunication windows (1300 and 1550 nm). In this regard, single self-assembled Quantum Dots (SAQDs) are well known solid-state semiconductor nano-structures that offer key advantages as single or entangled photon emitters fabricated on a GaAs substrate. SAQDs show confinement in all dimensions, leading to a 0-dimensional density of states similar to single atoms. The optical emission in the biexciton to neutral exciton cascade has been proposed as a deterministic polarization entangled photon source 4. Along the last decade, single SAQDs have been used to develop single 5 and entangled photon emitting diodes as sources of high fidelity Bell states 6. Single charge states have been controlled in order to manipulate hole spins with very large decoherence times 7 , which is a desirable property in the development of future quantum computing devices. High values of photon indistinguishability have also been obtained in two photon
We model the time-resolved and time-integrated photoluminescence of a single InAs/GaAs quantum do... more We model the time-resolved and time-integrated photoluminescence of a single InAs/GaAs quantum dot (QD) using a random population description. We reproduce the joint power dependence of the single QD exciton complexes (neutral exciton, neutral biexciton and charged trions). We use the model to investigate the selective optical pumping phenomenon, a predominance of the negative trion observed when the optical excitation is resonant to a non-intentional impurity level. Our experiments and simulations determine that the negative charge confined in the QD after exciting resonance to the impurity level escapes in 10 ns.
The room-temperature light emission of uncapped III-V semiconductor quantum dots is used to inves... more The room-temperature light emission of uncapped III-V semiconductor quantum dots is used to investigate the properties and evolution of the surface under exposure to a humid environment. Enhanced photoluminescence intensity resulting from exposure to polar molecules has already been reported; here we demonstrate that the external environment also has a relevant effect on the emission energy of quantum dots. Experimental results are interpreted on the basis of a model of the quantum system that takes into account the formation of oxide on pristine III-V surfaces and the presence of surface states. As a result of our study, we can clearly distinguish the effect of surface oxidation from that of surface state passivation on the emission of InAs surface quantum dots. This work sheds new light on the properties of semiconductor surface quantum dots as building blocks of novel and highly efficient sensing devices based on optical transduction.
New optical fiber based spectroscopic tools open the possibility to develop more robust and effic... more New optical fiber based spectroscopic tools open the possibility to develop more robust and efficient characterization experiments. Spectral filtering and light reflection have been used to produce compact and versatile fiber based optical cavities and sensors. Moreover, these technologies would be also suitable to study N-photon correlations, where high collection efficiency and frequency tunability is desirable. We demonstrated single photon emission of a single quantum dot emitting at 1300 nm, using a Fiber Bragg Grating for wavelength filtering and InGaAs Avalanche Photodiodes operated in Geiger mode for single photon detection. As we do not observe any significant fine structure splitting for the neutral exciton transition within our spectral resolution (46 μeV), metamorphic QD single photon emission studied with our all-fiber Hanbury Brown & Twiss interferometer could lead to a more efficient analysis of entangled photon sources at telecom wavelength. This all-optical fiber scheme opens the door to new first and second order interferometers to study photon indistinguishability, entangled photon and photon cross correlation in the more interesting telecom wavelengths. New emerging quantum optics technologies are mostly influenced by the possibility to design realistic proposals to implement and control quantum correlations between photons 1. Single photon and entangled photon emission has been demonstrated by different techniques and systems 2 , as for example by non-linear processes (parametric down conversion or four wave mixing) or by two level systems (atoms, molecules, Quantum Dots, single impurities or Nitrogen Vacancies in Diamond). However, an entangled photon source must fulfill several requirements for its use in quantum applications 3 : deterministic generation of entangled photons, high fidelity to the Bell state, high photon indistinguishability, and high efficiency. Although non-linear processes generate entangled photons at room temperature, two-level systems offer the opportunity to build a deterministic device, i.e., a system where entangled photons are emitted on demand by an external control (laser pulse or electrical signal). Furthermore, it is interesting to generate entangled photon emission compatible with optical fiber technologies, thus it is necessary to tune the optical emission to the second and third optical telecommunication windows (1300 and 1550 nm). In this regard, single self-assembled Quantum Dots (SAQDs) are well known solid-state semiconductor nano-structures that offer key advantages as single or entangled photon emitters fabricated on a GaAs substrate. SAQDs show confinement in all dimensions, leading to a 0-dimensional density of states similar to single atoms. The optical emission in the biexciton to neutral exciton cascade has been proposed as a deterministic polarization entangled photon source 4. Along the last decade, single SAQDs have been used to develop single 5 and entangled photon emitting diodes as sources of high fidelity Bell states 6. Single charge states have been controlled in order to manipulate hole spins with very large decoherence times 7 , which is a desirable property in the development of future quantum computing devices. High values of photon indistinguishability have also been obtained in two photon
We model the time-resolved and time-integrated photoluminescence of a single InAs/GaAs quantum do... more We model the time-resolved and time-integrated photoluminescence of a single InAs/GaAs quantum dot (QD) using a random population description. We reproduce the joint power dependence of the single QD exciton complexes (neutral exciton, neutral biexciton and charged trions). We use the model to investigate the selective optical pumping phenomenon, a predominance of the negative trion observed when the optical excitation is resonant to a non-intentional impurity level. Our experiments and simulations determine that the negative charge confined in the QD after exciting resonance to the impurity level escapes in 10 ns.
This chapter reviews approaches used to design and prepare structures for both the 1.3–1.6 μm spe... more This chapter reviews approaches used to design and prepare structures for both the 1.3–1.6 μm spectral window of low hydroxyl content optical fibres, and the 0.98–1.04 μm one for telecom and medical applications. In order to take full advantage of the peculiar optical properties of quantum dot (QD) nanostructures, their band structure must be engineered to optimize a few relevant parameters. Self-assembled semiconductor QDs have unique properties that make them extremely interesting for photonic devices with improved performances such as QD lasers. Such properties are intrinsic and are related to the zero-dimensional confinement of carriers in the structures. The chapter also demonstrates that how by a careful design of structures grown under well-defined conditions it is possible to cover the 0.98–1.04 μm and 1.3–1.6 μm windows with QD nanostructures based on GaAs substrates, a result that could open the path to the realization of QD photonic and optoelectronic devices for a wide range of applications.
Molecular beam epitaxy (MBE) is an epitaxial technology suited for the preparation of advanced st... more Molecular beam epitaxy (MBE) is an epitaxial technology suited for the preparation of advanced structures with composition and doping profiles controlled on a nanometer scale. The MBE growth mechanisms of both lowly (<2–3%) and highly lattice-mismatched structures allow the preparation of (1) two-dimensional structures with atomically smooth interfaces and (2) three-dimensional nanoislands that completely confine carriers, respectively. In this chapter, the main features of the MBE are reviewed and it is shown how the knowledge of kinetic growth mechanisms gives a great confidence in the design and preparation of structures with innovative engineered properties. Taking advantage of this feature, MBE has been used to demonstrate most of the novel semiconductor structures and devices of interest for photonics and electronics on the nanoscale.
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Papers by Luca Seravalli