Crecimiento por epitaxia de haces moleculares de puntos cuánticos de InAs sobre GaAs(001) con control en su lugar de formación para su integración en microcavidades ópticas

Quantum dots (QDs) are structures that show quantum confinement in all three directions of space. In particular semiconductor QDs are nanometric structures and they have great potential in the development of optoelectronic devices [1]. In particular, the optoelectronic devices that exploit the quantum properties of a single nanostructure [2] are of great interest in the field of cryptography and quantum information technologies [3] for their capability to generate non classical light states, such as single photon emission and entangled photon pair generation [4,5] and in the fundamental studies of cavity quantum electrodynamics (cQED) in solid state [6]. The development of this kind of devices exploits in many cases the light-matter coupling that takes place when an emitter is located in a high quality factor optical cavity. For the development of single photon sources, an increment of the emission rate is obtained due to Purcell effect [7]. Nevertheless, the fabrication of single QD-photonic mode coupled systems is nowadays a technological challenge; it is necessary to simultaneously achieve the spectral and spatial matching of the emission of the nanostructure and the photonic mode: the nanostructure emission wavelength should match the spectral position of the fundamental mode of the optical cavity and the nanostructure should be located at the highest electric field intensity of the photonic mode. Among other semiconductor systems, InAs/GaAs has been widely studied because of the high quality InAs quantum dots obtained by epitaxial Stranski-Krastanov selfassembly in GaAs(001) surface [8]. These self-assembled quantum dots (SAQDs) show high structural and optical quality s but they present an important practical drawback as it is not possible to know their nucleation site a priori. Due to the strict requirements for the fabrication of single nanostructure based devices, the development of fabrication processes to obtain site-controlled quantum dot (SCQDs) is mandatory. Establishing scalable fabrication processes of this kind of devices require to a priori define the spatial location of the active nanostructures. 224 Epitaxial growth on nanohole-patterned substrates has been established as the main technological approach to fabricate SCQDs [9,10]. Nanoholes patterned in the substrate surface can act as preferential nucleation sites for QD formation due to the surface chemical potential minima located at the bottom of these nanoholes, which in addition to the incorporation kinetics determines the SCQDs formation. Nevertheless, growth on patterned substrates imposes important limitations compared to the growth of QDs by means of self assembly processes. First, high resolution lithographic techniques are used for the fabrication of the patterned substrates and defects or contamination could be introduced in the substrate surface. Second, standard procedures in epitaxial growth, such as surface oxide thermal desorption and the growth of thick buffer layers, are not suitable for patterned substrates due to the need to preserve the patterned motifs. These limitations result in that the nanostructures are grown in proximity to the regrowth interface, which may degrade the optical properties of the obtained nanostructures [11]. Therefore, it is crucial to study and optimize all processes involved in the fabrication of SCQDs to obtain nanostructures with suitable properties for its practical application in devices. In addition, as many applications require the formation of a single QD at given positions in a reproducible process, it is mandatory to optimize the occupation statistics (number of QDs obtained per pattern motif) in the patterned motif

Low temperature oxide desorption in GaAs (111)A substrates

The aim of this work is to study oxide removal processes on GaAs (111) A substrates previous to epitaxial growth. We have studied conventional thermal desorption and processes based on the reduction of surface oxides by deposition of gallium, indium and exposure to atomic hydrogen. We have determined substrate temperatures (Ts) for optimum oxide removal in epi-ready substrates by the different studied processes: Ts = 540 °C for thermal desorption, Ts = 505 °C for indium deposition and Ts = 400 °C for oxide desorption by exposure to atomic hydrogen. All these processes allow for a subsequent good quality epitaxial growth. These results cannot be directly extended to oxide removal in grown samples that have been exposed to air outside the growth chamber. In this case, we have found that only indium deposition and exposure to atomic hydrogen are compatible with regrowth processes.We acknowledge financial support from Spanish MINECO (Grant TEC2011-29120-C05-04), and CAM (Grant S2009ESP-1503). Jesús Herranz acknowledges the JAE program for the funds.Peer Reviewe

Role of re-growth interface preparation process for spectral line-width reduction of single InAs site-controlled quantum dots

We present growth and optical characterization measurements of single InAs site-controlled quantum dots (SCQDs) grown by molecular beam epitaxy on GaAs (001) patterned substrates by atomic force microscopy oxidation lithography. InAs SCQDs directly grown on the patterned surface were used as a seed layer and strain template for the nucleation of optically active single InAs SCQDs. The preservation of the initial geometry of the engraved pattern motifs after the re-growth interface preparation process, the lack of buffer layer growth prior to InAs seed layer deposition and the development of suitable growth conditions provide us an improvement of the SCQDs' active layer optical properties while retaining a high ratio of single occupation (89%). In this work a fivefold reduction of the average optical line-width from 870 μeV to 156 μeV for InAs SCQDs located 15 nm from the re-growth interface is obtained by increasing the temperature of the initial thermal treatment step of the re-growth interface from 490 °C to 530 °C.The authors thank financial support by Spanish MINECO through grants ENE2012-37804-C02-02 and TEC2011-29120-C05-04. Jesús Herranz acknowledges the JAE program for the funds.Peer reviewe

Study of Growth Parameters for Single InAs QD Formation on GaAs(001) Patterned Substrates by Local Oxidation Lithography

This work studies the selective nucleation of InAs within nanoholes on GaAs(001) substrates patterned by atomic force microscopy local oxidation. The effects of substrate temperature and As4 overpressure during InAs deposition directly on the patterned substrate (without a GaAs buffer layer) are considered. It is found that when InAs is deposited at substrate temperature of 510 °C under low As4 overpressure, a single InAs quantum dot per nanohole is obtained for a broad range of sizes of pattern motifs. The use of these InAs quantum dots as seed nuclei for vertical stacking of optically active single InAs site-controlled quantum dots is investigated.The authors acknowledge financial support by Spanish MINECO through Grants ENE2012-37804-C02-02 and TEC2011-29120-C05-04. Jesús Herranz acknowledges the JAE program for funds.Peer reviewe

Low temperature oxide desorption in GaAs (111)A substrates

Trabajo presentado al 17th european Molecular Beam Epitaxy Workshop celebrado en Levi (Finlandia) del 10 al 13 de Marzo de 2013.Peer Reviewe

Contaminación lumínica en España 2010

A partir de imágenes nocturnas entre 1992 y 2007 de los satélites DMPS se ha obtenido una evolución por provincia del aumento de la emisión al luz espacio causante de la contaminación lumínica en España. El crecimiento medio nacional es del 54% en el periodo de estudio. Con los datos de INE y MITyC estimamos que el consumo nacional en alumbrado público es de 5.4 ±0.1 Twh/año a fecha de 2007. El objetivo nacional de consumo en alumbrado público anual es de 75 kwh por habitante. Sin embargo a partir de los datos oficiales calculamos que la media nacional está en 118 kwh por habitante en el año 2007 y crece

III-V semiconductor quantum dots for efficient quantum light sources

Comunicación presentada en el 3rd international Workshop Engineering of quantum emitter properties, celebrado en Linz (Austria) el 17 y 18 de diciembre de 2015.Photonic crystal microcavities (PCMs) with embedded quantum dots (QDs) have been shown as excellent test bed systems for experiments in the field of cavity quantum electrodynamics (c-QED) that may open doors to efficient quantum photonic devices for the generation of single-photons, entangled photon pairs and ultra-low threshold lasing. Based on fundamental excitonic emission and on biexciton-exciton recombination cascade, a single QD embedded in a PCM become efficient emitters of single photons or entangled photon pairs provided that both spectral and spatial matching of the optical cavity mode and the optical emission of the single nanostructure occur. Within this approach, we have explored several systems and growth methods with the aim of fabricating QD which fulfil the requirements for an efficient coupling between a single QD and a PCM. We have fabricated QD by molecular beam epitaxy (MBE) using a) droplet epitaxy and b) selective nucleation at nano-holes fabricated by atomic force microscopy local oxidation (AFMLO) lithography. Results will be presented of QD in GaAs/AlGaAs(111)A, InAs/GaAs(001) and InAs/InP (001). With the aim of obtaining coupled QD-PCM, we have followed two procedures: one is based on the fabrication of a PCM around a buried QD whose position and wavelength emission are previously determined; the other approach consists of locating a single QD by using AFMLO, at the maximum of the electric field of a prefabricated PCM. A MBE re-growth procedure has been developed for completing the PCM membrane thickness.Peer Reviewe

High quality factor GaAs-based photonic crystal microcavities by epitaxial re-growth

We investigate L7 photonic crystal microcavities (PCMs) fabricated by epitaxial re-growth of GaAs pre-patterned substrates, containing InAs quantum dots. The resulting PCMs show hexagonal shaped nano-holes due to the development of preferential crystallographic facets during the re-growth step. Through a careful control of the fabrication processes, we demonstrate that the photonic modes are preserved throughout the process. The quality factor (Q) of the photonic modes in the re-grown PCMs strongly depends on the relative orientation between photonic lattice and crystallographic directions. The optical modes of the re-grown PCMs preserve the linear polarization and, for the most favorable orientation, a 36% of the Q measured in PCMs fabricated by the conventional procedure is observed, exhibiting values up to ∼6000. The results aim to the future integration of site-controlled QDs with high-Q PCMs for quantum photonics and quantum integrated circuits. © 2013 Optical Society of America.The authors thank financial support by Spanish MINECO through grants ENE2012-37804-C02-02 and TEC2011-29120-C05-04, and by CAM through grants S2009/ESP-1503. IP, LW and JH acknowledge the FPI and JAE program for the funds.Peer Reviewe

Site control of InAs quantum dots on GaAs(001) substrates patterned by local oxidation Atomic Force Microscopy nanolithography

2 páginas, 3 figuras.-- Comunicación oral presentada al VI Congreso Español de Fuerzas y Túnel celebrado en Segovia (España) del 22 al 25 de Septiembre del 2008.This work was financed by Spanish MEC (TEC2005-05781-C03-01, NAN2004-09109-C04-01, Consolider-Ingenio 2010 CSD2006-00019), CAM (S 0505ESP 0200) and by the SANDIE Network of excellence (Contract nº NMP4-CT-2004-500101 group TEP-0120). JMS and PAG thanks to the I3P program.Peer reviewe