arXiv subjects

Agnieszka Gocalinska

Publications and source records attributed to Agnieszka Gocalinska.

11 recordsLinked to original sources

arXiv2025

Self-aligned pillar arrays embedding site-controlled single quantum dots for enhanced non-classical light emission

This work presents a foundational approach for fabricating arrays of self-aligned micro- and nanopillar structures incorporating individual site-controlled quantum dots (QDs) for enhanced light extraction. This method leverages the non-planar surface morphology of pyramidal QD samples to define dielectric masks self - aligned to the QD positions. The mask size, and consequently the lateral dimensions of the pillars, is precisely controlled through a chemical mechanical polishing step, obviating the need for any additional lithography step for creating the pillar. This fabrication technique offers several key advantages, including precise control over the pillar sites, and fully deterministic embedding of QD structures. The functionality of the structures was validated by integrating single In0.25Ga0.75As QDs - upon two-photon excitation of the biexciton state, the emission of single and polarization-entangled photon pairs was observed. Additionally, an extra fabrication step to deposit dome-like structures atop the pillars was demonstrated, effectively enhancing light extraction efficiency up to 12%.

physics.optics↗

arXiv2024

Evaluating the local bandgap across InxGa1-xAs multiple quantum wells in a metamorphic laser via low-loss EELS

Using high resolution scanning transmission electron microscopy and low-loss electron energy loss spectroscopy, we correlate the local bandgap (Eg), indium concentration, and strain distribution across multiple InxGa1-xAs quantum wells (QWs), on a GaAs substrate, within a metamorphic laser structure. Our findings reveal significant inhomogeneities, particularly near the interfaces, for both the indium and strain distribution, and subtle variations in the Eg across individual QWs. The interplay between strain, composition, and Eg was further explored by density functional theory simulations, indicating that variations in the Eg are predominantly influenced by the indium concentration, with strain playing a minor role. The observed local inhomogeneities suggest that differences between individual QWs may affect the collective emission and performance of the final device. This study highlights the importance of spatially resolved analysis in understanding and optimising the electronic and optical properties for designing of next-generation metamorphic lasers with multiple QWs as the active region.

cond-mat.mtrl-sci↗

arXiv2020

Micro-transfer printing high-efficiency GaAs photovoltaic cells onto silicon for wireless power applications

Here we report the development of high-efficiency microscale GaAs laser power converters, and their successful transfer printing onto silicon substrates, presenting a unique, high power, low-cost and integrated power supply solution for implantable electronics, autonomous systems and internet of things applications. We present 300 μm diameter single-junction GaAs laser power converters and successfully demonstrate the transfer printing of these devices to silicon using a PDMS stamp, achieving optical power conversion efficiencies of 48% and 49% under 35 and 71 W/cm2 808 nm laser illumination respectively. The transferred devices are coated with ITO to increase current spreading and are shown to be capable of handling very high short-circuit current densities up to 70 A/cm2 under 141 W/cm2 illumination intensity (~1400 Suns), while their open circuit voltage reaches 1235 mV, exceeding the values of pre-transfer devices indicating the presence of photon-recycling. These optical power sources could deliver Watts of power to sensors and systems in locations where wired power is not an option, while using a massively parallel, scalable, and low-cost fabrication method for the integration of dissimilar materials and devices.

physics.app-ph↗

arXiv2018

Vanishing biexciton binding energy from stacked, MOVPE grown, site-controlled pyramidal quantum dots for twin photon generation

We characterized stacked double-pyramidal quantum dots which showed biexciton binding energies close to zero by means of photoluminescence and cross-correlation measurements. It was possible to obtain a sequence of two photons with (nearly) the same energy from the biexciton-exciton-ground state cascade, as corroborated by a basic rate-equation model. This type of two-photon emission is both of relevance for fundamental quantum information theory studies as well as for more exotic applicative fields such as quantum biology.

cond-mat.mes-hall↗

arXiv2018

Three-dimensional Self-assembled Columnar Arrays of AlInP Quantum Wires for Polarized Micron-sized Amber Light Emitting Diodes

A three-dimensional ordered and self-organized semiconductor system emitting highly-polarized light in the yellow-orange visible range (580-650 nm) is presented, comprising self-assembled in-plane AlInP wires vertically stacked in regularly-spaced columns. More than 200 wires per column without detectable defect formation could be stacked. Theoretical simulations and temperature-dependent photoluminescence provided a benchmark to engineer multilayered structures showing internal quantum efficiency at room temperature larger than comparable quantum wells emitting at similar wavelengths. Finally, proof-of-concept light emitting diodes (LED) showed a high degree of light polarization and lower surface parasitic currents than comparable quantum well LEDs, providing an interesting perspective for high-efficiency polarized yellow-orange light emitting devices.

physics.app-ph↗

arXiv2016

Lithographyically defined, room temperature low threshold subwavelength red-emitting hybrid plasmonic lasers

Hybrid plasmonic lasers provide deep subwavelength optical confinement, strongly enhanced light-matter interaction and together with nanoscale footprint promise new applications in optical communication, bio-sensing and photolithography. The subwavelength hybrid plasmonic lasers reported so far often use bottom up grown nanowires, nanorods and nanosquares, making it difficult to integrate these devices into industry-relevant high density plasmonic circuits. Here, we report the first experimental demonstration of AlGaInP based, red-emitting hybrid plasmonic lasers at room temperature using lithography based fabrication processes. Resonant cavities with deep subwavelength 2D and 3D mode confinement of lambda square/56 and lambda cube/199, respectively are demonstrated. A range of cavity geometries (waveguides, rings, squares and disks) show very low lasing thresholds of 0.6-1.8 mJ/cm square with wide gain bandwidth (610 nm-685 nm), which are attributed to the heterogeneous geometry of the gain material, the optimized etching technique, and the strong overlap of the gain material with the plasmonic modes. Most importantly, we establish the connection between mode confinements and enhanced absorption and stimulated emission, which play a critical role in maintaining low lasing thresholds at extremely small hybrid plasmonic cavities. Our results pave the way for the further integration of dense arrays of hybrid plasmonic lasers with optical and electronic technology platforms.

cond-mat.mes-hall↗

arXiv2016

Issues related to the usage of nitrogen as carrier gas for the MOVPE growth of GaSb/InAs heterostructures on InAs pseudosubstrates

GaSb/InAs/GaSb layer stacks have been grown on InAs metamorphic substrates (pseudosubstrates) by MOVPE, using nitrogen as major carrier gas. We demonstrate that GaSb growth by nitrogen MOVPE on InAs metamorphic substrates (and on InAs wafers) is possible in a very narrow range of growth parameters. As demonstrators, GaSb/InAs/GaSb structures were grown for electron mobility tests, obtaining (unintentional) 2D electron gas densities in the order of 9/5x10e12 cm(e-2) and mobilities up to 1.2/1.8x10e4 cm(e2)/Vs at room and liquid nitrogen temperature respectively. We show that it is beneficial to have some hydrogen in the carrier gas mixture for GaSb growth to achieve good crystal quality, morphology and electrical properties. Furthermore, an unexpected and previously unreported decomposition process of GaSb is observed at relatively low growth temperatures under the supply of the precursors for InAs epitaxial overgrowth. This nevertheless gets suppressed at even lower growth temperatures.

cond-mat.mtrl-sci↗

arXiv2016

Indium segregation during III-V quantum wire and quantum dot formation on patterned substrates

We report a model for metalorganic vapor-phase epitaxy on non-planar substrates, specifically V-grooves and pyramidal recesses, which we apply to the growth of InGaAs nanostructures. This model, based on a set of coupled reaction-diffusion equations, one for each facet in the system, accounts for the facet-dependence of all kinetic processes (e.g., precursor decomposition, adatom diffusion, and adatom lifetimes) and has been previously applied to account for the temperature, concentration, and temporal-dependence of AlGaAs nanostructures on GaAs (111)B surfaces with V-grooves and pyramidal recesses. In the present study, the growth of In$_{0.12}$Ga$_{0.88}$As quantum wires at the bottom of V-grooves is used to determine a set of optimized kinetic parameters. Based on these parameters, we have modeled the growth of In$_{0.25}$Ga$_{0.75}$As nanostructures formed in pyramidal site-controlled quantum-dot systems, successfully producing a qualitative explanation for the temperature-dependence of their optical properties, which have been reported in previous studies. Finally, we present scanning electron and cross-sectional atomic force microscopy images which show previously unreported facetting at the bottom of the pyramidal recesses that allow quantum dot formation.

cond-mat.mtrl-sci↗

arXiv2015

Single pairs of time-bin entangled photons

Time-bin entangled photons are ideal for long-distance quantum communication via optical fibers. Here we present a source where, even at high creation rates, each excitation pulse generates at most one time-bin entangled pair. This is important for the accuracy and security of quantum communication. Our site-controlled quantum dot generates single polarization-entangled photon pairs, which are then converted, without loss of entanglement strength, into single time-bin entangled photon pairs.

quant-ph↗

arXiv2015

Evaluation of defect density by top-view large scale AFM on metamorphic structures grown by MOVPE

We demonstrate an atomic force microscopy based method for estimation of defect density by identification of threading dislocations on a non-flat surface resulting from metamorphic growth. The discussed technique can be applied as an everyday evaluation tool for the quality of epitaxial structures and allow for cost reduction, as it lessens the amount of the transmission electron microscopy analysis required at the early stages of projects. Metamorphic structures with low surface defectivities (below 106) were developed successfully with the application of the technique, proving its usefulness in process optimisation.

cond-mat.mtrl-sci↗

arXiv2014

Towards quantum dot arrays of entangled photon emitters

We show that with a new family of pyramidal site-controlled InGaAsN quantum dots it is possible to obtain areas containing as much as 15% of polarization-entangled photon emitters - a major improvement if compared to the small fraction achievable by other quantum dot systems. Entanglement is attested by a two-photon polarization state density matrix and the parameters obtained from it. Emitters showing fidelities up to 0.721+-0.043 were found.

cond-mat.mes-hall↗