arXiv subjects

E. Pelucchi

Publications and source records attributed to E. Pelucchi.

At least 19 recordsLinked to original sources

arXiv2025

Trion quantum coherence in site-controlled pyramidal InGaAs quantum dots

Deterministically positioned pyramidal InGaAs quantum dots (QDs) exhibit exceptional quantum properties, making them highly promising candidates for scalable on-chip quantum information processing. In this work, we investigate the coherent dynamics of positively charged excitons under the influence of strong magnetic fields in the Faraday configuration. Pyramidal quantum dots exhibit a fourfold splitting of the charged excitons even in the Faraday configuration, giving rise to an optically addressable double-Lambda{\Lambda} system akin to self-assembled quantum dots in oblique magnetic fields. Here, we investigate ultrafast complete coherent control of the trion to ground state transition utilizing advanced optical resonant excitation techniques and we observe quantum coherence over timescales that are similar to other prominent quantum dot platforms. These results pave the way towards establishing site-controlled pyramidal InGaAs QDs as scalable platforms for quantum information processing, expanding the reach of coherent control to new quantum systems.

quant-ph↗

arXiv2025

Optical pumping and initialization of a hole spin in site-controlled InGaAs pyramidal quantum dots

We investigate site-controlled In$_{0.25}$Ga$_{0.75}$As quantum dots in (111)B GaAs pyramidal recesses as spin qubits. Combining scanning confocal cryomicroscopy, magneto-photoluminescence studies and resonant excitation, we identify and isolate a positively charged exciton with a hole-spin in its ground state. Application of a strong 5 T magnetic field parallel to the growth axis, induces a fourfold splitting of the energy levels of the positively charged exciton creating an optically addressable double-lambda system. We combine weak above-band and resonant excitation to demonstrate spin pumping and high-fidelity spin initialization through all four optical transitions and study the system behavior as a function of the resonant driving strength showing the existence of a robust spin that can be optically pumped and initialized. These results demonstrate the potential of these quantum dots for precise spin manipulation and their relevance for future quantum hardware.

cond-mat.mes-hall↗

arXiv2017

Statistical study of stacked/coupled site-controlled pyramidal quantum dots and their excitonic properties

We report on stacked multiple quantum dots (QDs) formed inside inverted pyramidal recesses, which allow for the precise positioning of the QDs themselves. Specifically we fabricated double QDs with varying inter-dot distance and ensembles with more than two nominally highly symmetric QDs. For each, the effect of the interaction between QDs is studied by characterizing a large number of QDs through photoluminescence spectroscopy. A clear red-shift of the emission energy is observed together with a change in the orientation of its polarization, suggesting an increasing interaction between the QDs. Finally we show how stacked QDs can help influencing the charging of the excitonic complexes.

cond-mat.mes-hall↗

arXiv2017

Engineering of selective carrier injection in patterned arrays of single-quantum-dot entangled photon light-emitting diodes

Scalability and foundry compatibility (as for example in conventional silicon based integrated computer processors) in developing quantum technologies are exceptional challenges facing current research. Here we introduce a quantum photonic technology potentially enabling large scale fabrication of semiconductor-based, site-controlled, scalable arrays of electrically driven sources of polarization-entangled photons, with the potential to encode quantum information. The design of the sources is based on quantum dots grown in micron-sized pyramidal recesses along the crystallographic direction (111)B theoretically ensuring high symmetry of the quantum dots - the condition for actual bright entangled photon emission. A selective electric injection scheme in these non-planar structures allows obtaining a high density of light-emitting diodes, with some producing entangled photon pairs also violating Bell's inequality. Compatibility with semiconductor fabrication technology, good reproducibility and control of the position make these devices attractive candidates for integrated photonic circuits for quantum information processing.

physics.app-ph↗

arXiv2017

Excitonic lasing of strain-free InP(As) quantum dots in AlInAs microdisk

Formation, emission and lasing properties of strain-free InP(As)/AlInAs quantum dots (QDs) embedded in AlInAs microdisk (MD) cavity were investigated using transmission electron microscopy and photoluminescence (PL) techniques. In MD structures, the QDs having nano-pan-cake shape have height of ~2 nm, lateral size of 20-50 nm and density of ~5x109 cm-2. Their emission observed at ~940 nm revealed strong temperature quenching, which points to exciton decomposition. It also showed unexpected type-I character indicating In-As intermixing, as confirmed by band structure calculations. We observed lasing of InP(As) QD excitons into whispering gallery modes in MD having dimeter ~3.2 mkm and providing free spectral range of ~27 nm and quality factors up to Q~13000. Threshold of ~50 W/cm2 and spontaneous emission coupling coefficient of ~0.2 were measured for this MD-QD system.

physics.optics↗

arXiv2017

Tuning InP self-assembled quantum structures to telecom wavelength: a versatile original InP(As) nanostructure "workshop"

The influence of hydride exposure on previously unreported self-assembled InP(As) nanostructures is investigated, showing an unexpected morphological variability with growth parameters, and producing a large family of InP(As) nanostructures by metalorganic vapour phase epitaxy, from dome and ring-like structures to double dot in a ring ensembles. Moreover, preliminary microphotoluminescence data are indicating the capped rings system as an interesting candidate for single quantum emitters at telecom wavelengths, potentially becoming a possible alternative to InAs QDs for quantum technology and telecom applications.

cond-mat.mes-hall↗

arXiv2016

Unexpected aspects of strain relaxation and compensation in InGaAs metamorphic structures grown by MOVPE

We present a selection of stack designs for MOVPE grown InxGa1-xAs metamorphic buffer layers following various convex-down compositional continuous gradients of the In content, showing that defect generation and strain can be managed in a variety of ways, some rather unexpected (and unreported). Indeed, we observe that it is possible to grow surprisingly thick tensile strained layers on metamorphic substrates, without significant relaxation and defect generation. We believe our findings give significant insights to the investigation of strain, relaxation and defect distribution in metamorphic buffer design, so to obtain properly engineered/tailored structures (the most successful ones already finding applications in device growth).

cond-mat.mtrl-sci↗

arXiv2015

Conditions for entangled photon emission from (111)B site-controlled Pyramidal quantum dots

A study of highly symmetric site-controlled Pyramidal In0.25Ga0.75As quantum dots (QDs) is presented. It is discussed that polarization-entangled photons can be also obtained from Pyramidal QDs of different designs from the one already reported in Juska et al. (Nat. Phot. 7, 527, 2013). Moreover, some of the limitations for a higher density of entangled photon emitters are addressed. Among these issues are (1) a remaining small fine-structure splitting and (2) an effective QD charging under non-resonant excitation conditions, which strongly reduce the number of useful biexciton-exciton recombination events. A possible solution of the charging problem is investigated exploiting a dual-wavelength excitation technique, which allows a gradual QD charge tuning from strongly negative to positive and, eventually, efficient detection of entangled photons from QDs, which would be otherwise ineffective under a single-wavelength (non-resonant) excitation.

quant-ph↗

arXiv2014

Complex optical signatures from quantum dot nanostructures and behavior in inverted pyramidal recesses

A study of previously overlooked structural and optical properties of InGaAs heterostructures grown on (111)B oriented GaAs substrates patterned with inverted 7.5 um pitch pyramidal recesses is presented. First, the composition of the confinement barrier material (GaAs in this work) and its growth temperature are shown as some of the key parameters that determine the main quantum dot properties, including nontrivial emission energy dependence, excitonic pattern and unusual photoluminescence energetic ordering of the InGaAs ensemble nanostructures. Secondly, the formation of a formerly unidentified type of InGaAs nanostructures - three corner quantum dots - is demonstrated in our structures next to the well-known ones (a quantum dot and three lateral quantum wires and quantum wells). The findings show the complexity of the pyramidal quantum dot system which strongly depends on the sample design and which should be considered when selecting highly symmetric (central) quantum dots in newly designed experimental projects.

cond-mat.mtrl-sci↗

arXiv2014

Unusual nanostructures of "lattice matched" InP on AlInAs

We show that the morphology of the initial monolayers of InP on Al0.48In0.52As grown by metalorganic vapor-phase epitaxy does not follow the expected layer-by-layer growth mode of lattice-matched systems, but instead develops a number of low-dimensional structures, e.g., quantum dots and wires. We discuss how the macroscopically strain-free heteroepitaxy might be strongly affected by local phase separation/alloying-induced strain and that the preferred aggregation of adatom species on the substrate surface and reduced wettability of InP on AlInAs surfaces might be the cause of the unusual (step) organization and morphology

cond-mat.mtrl-sci↗

arXiv2013

Transient and self-limited nanostructures on patterned surfaces

Site-controlled quantum dots formed during the deposition of (Al)GaAs layers by metalorganic vapor-phase epitaxy on GaAs(111)B substrates patterned with inverted pyramids result in geometric and compositional self-ordering along the vertical axis of the template. We describe a theoretical scheme that reproduces the experimentally-observed time-dependent behavior of this process, including the evolution of the recess and the increase of Ga incorporation along the base of the template to stationary values determined by alloy composition and other growth parameters. Our work clarifies the interplay between kinetics and geometry for the development of self-ordered nanostructures on patterned surfaces, which is essential for the reliable on-demand design of confined systems for applications to quantum optics.

cond-mat.mtrl-sci↗

arXiv2012

Surface organization of homoepitaxial InP films grown by metalorganic vapor-phase epitaxy

We present a systematic study of the morphology of homoepitaxial InP films grown by metalorganic vapor-phase epitaxy which are imaged with ex situ atomic force microscopy. These films show a dramatic range of different surface morphologies as a function of the growth conditions and substrate (growth temperature, V/III ratio, and miscut angle < 0.6deg and orientation toward A or B sites), ranging from stable step flow to previously unreported strong step bunching, over 10 nm in height. These observations suggest a window of growth parameters for optimal quality epitaxial layers. We also present a theoretical model for these growth modes that takes account of deposition, diffusion, and dissociation of molecular precursors, and the diffusion and step incorporation of atoms released by the precursors. The experimental conditions for step flow and step bunching are reproduced by this model, with the step bunching instability caused by the difference in molecular dissociation from above and below step edges, as was discussed previously for GaAs (001).

cond-mat.mtrl-sci↗

arXiv2012

Semiconductor nanostructures engineering: Pyramidal quantum dots

Pyramidal quantum dots (QDs) grown in inverted recesses have demonstrated over the years an extraordinary uniformity, high spectral purity and strong design versatility. We discuss recent results, also in view of the Stranski-Krastanow competition and give evidence for strong perspectives in quantum information applications for this system. We examine the possibility of generating entangled and indistinguishable photons, together with the need for the implementation of a, regrettably still missing, strategy for electrical control.

cond-mat.mes-hall↗

arXiv2012

Suppression of threading defects formation during Sb-assisted metamorphic buffer growth in InAs/InGaAs/InP structure

A virtual substrate for high quality InAs epitaxial layer has been attained via metalorganic vapor-phase epitaxy growth of Sb-assisted InxGa1-xAs metamorphic buffers, following a convex compositional continuous gradient of the In content from x = 53 % to 100 %. The use of trimethylantimony (or its decomposition products) as a surfactant has been found to crucially enable the control over the defect formation during the relaxation process. Moreover, an investigation of the wafer offcut-dependence of the defect formation and surface morphology has enabled the achievement of a reliably uniform growth on crystals with offcut towards the [111]B direction.

cond-mat.mtrl-sci↗

arXiv2011

Wettability and "petal effect" of GaAs native oxides

We discuss unreported transitions of oxidized GaAs surfaces between (super)hydrophilic and hydrophobic states when stored in ambient conditions. Contact angles higher than 90deg and high adhesive force were observed for several air-aged epitaxial samples grown under different conditions as well as on epi-ready wafers. Regardless of the morphologies of the surface, superhydrophilicity of oxygen-plasma treated samples was observed, an effect disappearing with storage time. Reproducible hydrophobicity was likewise observed, as expected, after standard HCl surface etching. The relation between surface oxides and hydrophobic/hydrophilic behavior is discussed.

cond-mat.mtrl-sci↗

arXiv2011

Impact of Nitrogen incorporation on pseudomorphic site-controlled quantum dots grown by Metalorganic Vapour Phase Epitaxy

We report on some surprising optical properties of diluted nitride InGaAs_(1-y)N_y /GaAs (y<<1) pyramidal site-controlled quantum dots, grown by metalorganic vapor phase epitaxy on patterned GaAs (111)B substrates. Microphotoluminescence characterizations showed antibinding exciton/ biexciton behavior, a spread of exciton lifetimes in an otherwise very uniform sample, with unexpected long neutral exciton lifetimes (up to 7 ns) and a nearly zero fine structure splitting on a majority of dots.

cond-mat.mtrl-sci↗

arXiv2011

AlGaAs/GaAs/AlGaAs quantum wells as a sensitive tool for the MOVPE reactor environment

We present in this work a simple Quantum Well (QW) structure consisting of GaAs wells with AlGaAs barriers as a probe for measuring the performance of arsine purifiers within a MetalOrganic Vapour Phase Epitaxy system. Comparisons between two different commercially available purifiers are based on the analysis of low temperature photoluminescence emission spectra from thick QWs, grown on GaAs substrates misoriented slightly from (100). Neutral excitons emitted from these structures show extremely narrow linewidths, comparable to those which can be obtained by Molecular Beam Epitaxy in an ultra-high vacuum environment, suggesting that purifications well below the 1ppb level are needed to achieve high quality quantum well growth.

cond-mat.mtrl-sci↗

arXiv2011

Decomposition, diffusion, and growth rate anisotropies in self-limited profiles during metalorganic vapor-phase epitaxy of seeded nanostructures

We present a model for the interplay between the fundamental phenomena responsible for the formation of nanostructures by metalorganic vapour phase epitaxy on patterned (001)/(111)B GaAs substrates. Experiments have demonstrated that V-groove quantum wires and pyramidal quantum dots form as a consequence of a self-limiting profile that develops, respectively, at the bottom of V-grooves and inverted pyramids. Our model is based on a system of reaction-diffusion equations, one for each crystallographic facet that defines the pattern, and include the group III precursors, their decomposition and diffusion kinetics (for which we discuss the experimental evidence), and the subsequent diffusion and incorporation kinetics of the group-III atoms released by the precursors. This approach can be applied to any facet configuration, including pyramidal quantum dots, but we focus on the particular case of V-groove templates and offer an explanation for the self-limited profile and the Ga segregation observed in the V-groove. The explicit inclusion of the precursor decomposition kinetics and the diffusion of the atomic species revises and generalizes the earlier work of Basiol et al. [Phys. Rev. Lett. 81, 2962 (1998); Phys. Rev. B 65, 205306 (2002)] and is shown to be essential for obtaining a complete description of self-limiting growth. The solution of the system of equations yields spatially resolved adatom concentrations, from which average facet growth rates are calculated. This provides the basis for determining the conditions that yield selflimiting growth. The foregoing scenario, previously used to account for the growth modes of vicinal GaAs(001) during MOVPE and the step-edge profiles on the ridges of vicinal surfaces patterned with V-grooves, can be used to describe the morphological evolution of any template composed of distinct facets.

cond-mat.mtrl-sci↗