Absorption features of the zero frequency mode in an ultra-thin slab

© 2014 AIP Publishing LLC. The optical absorption in a homogeneous and non-dispersive slab is governed by the well-known Fabry-Perot resonances. We have found that below the lowest order Fabry-Perot resonance, there is another absorption maximum due to the zero frequency mode whose peak frequency is given not by the real part of the complex resonance frequency, as it is the case for all other resonances, but by the imaginary part. This result is of interest, among other applications, for ultra thin solar cells, as tuning the zero frequency mode peak with the maximum of solar irradiance results in an increased efficiency.This work has been supported by Spanish MINECO (Grant Nos. ENE2012-37804-C02-02 and TEC2011-29120-C05-04).Peer Reviewe

Photonics Crystals on high efficiency III-V Solar Cells

Póster presentado en la 28th European PV Solar Energy Conference and Exhibition (EU PVSEC 2013), celebrada en París del 30 de septiembre al 4 de octubre de 2013.We have explored the following photon management options for increasing the efficiency of concentrator solar cells: increasing the voltage by recycling the luminescence, increasing the current reducing reflection and increasing the optical path. We find that a 1m m thick GaAs solar cell with optimized nanostructured front and back surfaces has significantly higher efficiency than a similar cell with a perfect back side mirror and a state of the art bilayer antireflective coating. We have also designed a multilayer coating with high reflectivity at angles away from the surface normal that results in luminescence trapping, and thus increases the open circuit voltage and the cell efficiency.Peer Reviewe

Photon management with nanostructures on concentrator solar cells

Optimizing the feature sizes of dielectric nanostructures on the top (ZnS) and bottom (SiO2) surfaces of a 1 μm thick GaAs solar cell, we obtain a higher efficiency (34.4%) than a similar cell with a state of the art bilayer antireflection coating and a planar mirror (33.2%). The back side nanostructure increases the photocurrent due to enhanced optical path length inside the semiconductor, while the nanostructure on the front side increases the photocurrent due to lower reflectance losses. © 2013 AIP Publishing LLC.We acknowledge the SGAI-CSIC for the allocation of computational resource and the financial support by MINECO (ENE2012-37804-C02-02, FPI grant) and CAM (S2009/ENE-1477).Peer Reviewe

Post-growth rapid thermal annealing of InAs quantum dots grown on GaAs nanoholes formed by droplet epitaxy

Trabajo presentado al 16th European Molecular Beam Epitaxy Workshop celebrado en Alpe d'Huez (Francia) del 20 al 23 de Marzo de 2011.The deposition of InAs on GaAs nanoholes formed by droplet epitaxy can be used to tailor the shape and size of InAs QDs while preserving the low areal density (~2x108 cm-2) imposed by the nanohole pattern. Our previous micro photoluminescence (μPL) study of individual InAs QDs grown by this method revealed that the single QD emission was largely affected by the charged environment surrounding the nanostructure. This charged environment, attributed to the presence of As vacancies, leads to multicharged exciton emission and spectral diffusion effects which might limit the suitability of these QDs in quantum light emitting applications. An intense single peaked emission with radiation limited linewidth and null fine structure splitting (FSS) would be desirable to fully exploit the size and shape control capabilities of droplet epitaxy based methods. The aim of the present study is to reduce the presence of the As vacancies near the QDs by applying a post-growth rapid thermal annealing (RTA) to the sample. Besides, the small FSS (~41 μeV) [1] found typically in theseQDs might be reduced further by the RTA processes. Figure 1 shows the ensemble PL of our sample before and after the RTA process at 775º C during 5 minutes. The optimization of the growth procedure explained in [1] gives rise to a narrow emission band centered at 1.296 eV with FWHM=14.6 meV. A blue shift of the PL band and a reduction of the decay time are clearly observed after the RTA without noticeable change of the FWHMT. o study the same single QDs before and after the RTA process we have defined arrays of 2-μm-wide mesa structures on the sample surface (inset Fig. 2). Before the RTA, the s-shell emission is dominated by multicharged exciton complexes and shows narrow emission linewidths (<100 μeV) limited by our spectrometer resolution (Fig. 2). Results after RTA process will be shown.Peer Reviewe

Silicon nanowires: where mechanics and optics meet at the nanoscale

Mechanical transducers based on nanowires promise revolutionary advances in biological sensing and force microscopy/spectroscopy. A crucial step is the development of simple and non-invasive techniques able to detect displacements with subpicometer sensitivity per unit bandwidth. Here, we design suspended tapered silicon nanowires supporting a range of optical resonances that confine and efficiently scatter light in the visible range. Then, we develop an optical method for efficiently coupling the evanescent field to the regular interference pattern generated by an incoming laser beam and the reflected beam from the substrate underneath the nanowire. This optomechanical coupling is here applied to measure the displacement of 50 nm wide nanowires with sensitivity on the verge of 1 fm/Hz1/2 at room temperature with a simple laser interferometry set-up. This method opens the door to the measurement of the Brownian motion of ultrashort nanowires for the detection of single biomolecular recognition events in liquids, and single molecule spectroscopy in vacuum.We acknowledge financial support from the Spanish Science Ministry (MINECO) through projects TEC2011-29120-C05-04; and from European Research Council through Starting Grant NANOFORCELLS (ERC-StG-2011-278860).Peer reviewe

Strain driven migration of In during the growth of InAs/GaAs quantum posts

Using the mechano-optical stress sensor technique, we observe a counter-intuitive reduction of the compressive stress when InAs is deposited on GaAs (001) during the growth of quantum posts. Through modelling of the strain fields, we find that such anomalous behaviour can be related to the strain-driven detachment of In atoms from the crystal and their surface diffusion towards the self-assembled nanostructures.We acknowledge the financial support by Spanish MINECO through Grant Nos. ENE2012-37804-C02-02 and TEC2011-29120-C05-04, and by Spanish CAM through Grant Nos. S2009/ESP-1503 and S2009/ENE-1477.Peer Reviewe

Theoretical modelling of quaternary GaInAsSb/GaAs self-assembled quantum dots

Trabajo presentado al "Quantum Dot", celebrado en Nottingham (UK) del 26 al 30 de Abril de 2010.InAs/GaAs quantum dots exposed to Sb after growth exhibit spectral changes. We study in the present paper an idealized nanostructure consisting of a homogeneous distribution of the quaternary GaInAsSb surrounded by a barrier of GaAs. We nd that the valence band o set is a critical parameter in modelling its electronic structure. Depending on this value, we predict a transition from type-I to type-II band alignment at a di erent Sb concentration. The addition of Sb to reduce the transition energy while keeping a type-I alignment is only of bene t at low Sb concentrationThis work was supported by the Spanish MICINN (projects TEC2008-06756-C03-01/02/TEC, CONSOLIDER INGENIO 2010 CSD2006-0019 and CSD2009-00013), the Junta de Andalucía (PAI research groups TEP-120 and TIC-145; project P08-TEP-03516) and Comunidad Autónoma de Madrid S2009ESP-1503.Peer reviewe

Voltage tuning of exciton topology and g-factor in type-II InAs/GaAsSb quantum dots

Trabajo presentado en la DPG Conference - Geometry and Topology Controlled Nanoarchitectures, celebrada en Berlín (alemania), del 11 al 16 de marzo de 2018Peer reviewe

Type-II Quantum Dots with Topology Driven g-factor tunability

Trabajo presentado en el ICSNN2018: 20th International Conference on Superlattices Nanostructures and Nanodevices, celebrado en Madrid del 23 al 27 de julio de 2018Peer reviewe

Inverse Design of a Hybrid Mie-Tamm Photonic Structure as a Highly Directional Gigahertz Single-Photon Source

We present a photonic structure in which Mie, Tamm, and surface-plasmon optical modes can be tailored to enhance the brightness of an embedded single-photon emitter. Contrary to most proposals, the structure is designed for excitation and collection through the substrate side. The front surface can be used instead to arrange metal contacts which serve the purpose of both electrical gates and optical mirrors. The design is particularized for InGaAs quantum dots on GaAs, resulting in an out-coupled single-photon rate exceeding 3 GHz in a cone of narrow numerical aperture (NA=0.17). The fabrication tolerances are also discussed.This work is supported by the European Union Horizon 2020 research and innovation program under Marie Skłodowska-Curie Grant Agreement No. 956548, project Quantimony. This project (20FUN05 SEQUME) has received funding from the EMPIR program, cofinanced by the Participating States, and from the European Union Horizon 2020 research and innovation program, the Agencia Estatal de Investigación (AEI) through Grant No. PID2019-106088RB-C31, and the CSIC Interdisciplinary Thematic Platform (PTI+) on Quantum Technologies (PTI-QTEP+)