Publications by Ivan Prieto
The early growth stage of GaAs by metal organic vapor phase epitaxy on a novel kind of Si substra... more The early growth stage of GaAs by metal organic vapor phase epitaxy on a novel kind of Si substrate is investigated. The substrate consists of nanotips (NTs) fabricated on a Si(001) wafer by means of lithography and reactive ion etching. 3D GaAs nanocrystals are found to nucleate with a probability of 90% on the (n0m), (–n0m), (0nm), and (0–nm) facets (n, m integers) of these NTs. Additionally, in terms of nucleation yield, an average of 2 GaAs nanocrystals in each of those facets is observed. By contrast, facets of type {±nnm} remain virtually free of any 3D nuclei. A simple model based on the kinetics of the growth is used to explain the facet selective 3D nucleation. The model is consistent with a similar selectivity observed on micrometer-sized substrate features.
Nano-heteroepitaxial growth of GaAs on Si(001) by metal organic vapor phase epitaxy was investiga... more Nano-heteroepitaxial growth of GaAs on Si(001) by metal organic vapor phase epitaxy was investigated to study emerging materials phenomena on the nano-scale of III–V/Si interaction. Arrays of Si nano-tips (NTs) embedded in a SiO 2 matrix were used as substrates. The NTs had top Si openings of 50–90 nm serving as seeds for the selective growth of GaAs nano-crystals (NCs). The structural and morphological properties were investigated by high resolution scanning electron microscopy, atomic force microscopy, electron backscatter diffraction, x-ray diffraction, and high resolution scanning transmission electron microscopy. The GaAs growth led to epitaxial NCs featuring a bi-modal distribution of size and morphology. NCs of small size exhibited high structural quality and well-defined {111}–{100} faceting. Larger clusters had less regular shapes and contained twins. The present work shows that the growth of high quality GaAs NCs on Si NTs is feasible and can provide an alternate way to the integration of compound semiconductors with Si micro-and opto-electronics technology.
We present the nanoheteroepitaxial growth of gallium arsenide (GaAs) on nano-patterned silicon (S... more We present the nanoheteroepitaxial growth of gallium arsenide (GaAs) on nano-patterned silicon (Si) (001) substrates fabricated using a CMOS technology compatible process. The selective growth of GaAs nano-crystals (NCs) was achieved at 570 °C by MOVPE. A detailed structure and defect characterization study of the grown nano-heterostructures was performed using scanning transmission electron microscopy, x-ray diffraction, micro-Raman, and micro-photoluminescence (μ-PL) spectroscopy. The results show single-crystalline, nearly relaxed GaAs NCs on top of slightly, by the SiO 2-mask compressively strained Si nano-tips (NTs). Given the limited contact area, GaAs/Si nanostructures benefit from limited intermixing in contrast to planar GaAs films on Si. Even though a few growth defects (e.g. stacking faults, micro/nano-twins, etc) especially located at the GaAs/Si interface region were detected, the nanoheterostructures show intensive light emission, as investigated by μ-PL spectroscopy. Achieving well-ordered high quality GaAs NCs on Si NTs may provide opportunities for superior electronic, photonic, or photovoltaic device performances integrated on the silicon technology platform.
Electrical contacts on the top surface of solar cells and light emitting diodes cause shadow loss... more Electrical contacts on the top surface of solar cells and light emitting diodes cause shadow losses. The phenomenon of extraordinary optical transmission through arrays of subwavelength holes suggests the possibility of engineering such contacts to reduce the shadow using plasmonics, but resonance effects occur only at specific wavelengths. Here we describe instead a broadband effect of enhanced light transmission through arrays of subwavelength metallic wires, due to the fact that, in the absence of resonances, metal wires asymptotically tend to invisibility in the small size limit regardless of the fraction of the device area taken up by the contacts. The effect occurs for wires more than an order of magnitude thicker than the transparency limit for metal thin films. Finite difference in time domain calculations predict that it is possible to have high cloaking efficiencies in a broadband wavelength range, and we experimentally demonstrate contact shadow losses less than half of the geometric shadow. The contacts in optoelectronic devices have two competing requirements: low electrical resistivity, and high light transmittance. To date, this trade-off has limited the performance of optoelectronic devices such as solar cells and light emitting diodes (LEDs). The first proposals to direct light away from the top contacts appeared not long after the birth of photovoltaics, but these schemes based on ray tracing optics (such as microlenses) suffer from added complexity, and fail to work when there are features not much larger than the light wavelength 1,2. Recent advances in nanowire technology have improved the contact characteristics of low power density devices 3,4 , but still result in shadow losses that are unacceptable for concentrator solar cells and other high power density devices such as LEDs. For devices operating at specific wavelengths (which is not the case for solar cells), this difficulty can perhaps be overcome by engineering plasmonic resonant effects 5,6. Transparent conductive oxides such as indium tin oxide (ITO) offer sufficient performance (90% transmission with an 11 Ω/sq sheet resistance) for devices operating at low current densities, such as flat panel displays and organic LEDs 7. The scarcity of Indium has motivated research into alternatives such as the organic polymer PEDOT:PSS, with 91% transmission and 226 Ω/sq sheet resistance 8. Van de Groep et al. have demonstrated silver nanowire network arrays on glass with 89% transmission and 20 Ω/sq sheet resistance 9 , and the group of Prof. Cui has perfected metal nanowire fabrication from electrospun fibres, reaching 90% transmittance and 2 Ω/sq sheet resistance 4. State of the art multi-junction solar cells require noble metal top contact grids with > 95% transmittance and < 10 Ω/sq sheet resistance to operate at high sunlight concentrations (> 500 suns) 10,11. Here we demonstrate nanowire arrays with a sheet resistance of 2.5 Ω/sq at 96.4% transmission (with a long period array), and 0.31 Ω/sq at 91% transmission (with a short period array). We show that optimized metal nanowires cast an effective shadow much smaller than the geometric shadow, and consequently, optoelectronic devices can be designed in a way that significantly reduces the losses due to the top contact, overcoming the previously mentioned trade-off. The effect is applicable to a wide range of technical problems, such as contacts in solar cells, light emitting diodes (LEDs) and flat panel displays, but here we focus our attention on concentrator photovoltaics (CPV), perhaps the most demanding of these due to the need to minimize losses across a broadband wavelength range. Recent interest in plasmonic solar cells has primarily been focused on increasing the optical path length or near field intensity in optically thin solar cells by adding components such as nanoparticles or diffraction gratings 12–14. Instead, we focus on nanostructuring an already existing and necessary component, the front contact , to reduce shadow losses 12. The questions addressed in this work are best understood on the basis of the analytical solution for the interaction of the electromagnetic field with a freestanding metal cylinder 15,16. In the small size limit (when the ratio of
The authors demonstrate high aspect ratio and large area metallic nanogrids as transparent electr... more The authors demonstrate high aspect ratio and large area metallic nanogrids as transparent electrodes with reduced series resistance on GaAs based optoelectronic devices. The fabrication process uses ultraviolet photolithography techniques, pulsed reactive ion etching, and two metallization steps: a vapor deposited contact seed layer and a thickening step by electrodeposition. As a result, a threefold reduction in resistive power losses is achieved with a contact grid transmission comparable to state-of-the-art devices.
This document provides supplementary information to "Near thresholdless laser operation at room t... more This document provides supplementary information to "Near thresholdless laser operation at room temperature," http://dx.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures
The authors demonstrate high quality factor GaAs-based L9 photonic crystal microcavities (PCMs) w... more The authors demonstrate high quality factor GaAs-based L9 photonic crystal microcavities (PCMs) with embedded InAsSb quantum dots with emission in 1.3 lm at room temperature. The fabrication process uses reactive ion beam etching with a CHF 3 /N 2 gas mixture and reactive ion etching with a BCl 3 /N 2 gas mixture to form PCMs on air-suspended slabs. An optimum N 2 partial flux content of 0.65 and a successful removal of deposits formed during the membrane release by a fast wet etching in HF provide optical quality factors (Q-factors) as high as $30 000.
Optics Express, Dec 13, 2013
We investigate L7 photonic crystal microcavities (PCMs) fabricated by epitaxial re-growth of GaAs... more 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.
We demonstrate an information transfer mechanism between two dissimilar remote InAs/GaAs quantum ... more We demonstrate an information transfer mechanism between two dissimilar remote InAs/GaAs quantum dots weakly coupled to a common photonic crystal microcavity. Bichromatic excitation in the s state of one of the dots leads to the formation of dressed states due to the coherent coupling to the laser field, in resonance with the quantum dot. Information on the resulting dressed structure is read out through the photoluminescence spectrum of the other quantum dot, as well as the cavity mode. The effect is also observed upon exchange of the excitation and detection quantum dots. This quantum dot intertalk is interpreted in terms of a cavity-mediated coupling involving acoustic phonons. A master equation for a three-level system coherently pumped by the two lasers quantitatively describes the behavior of our system. Our result presents an important step towards scalable solid-state quantum networking based on coupled multi-quantum-dot-cavity systems, without the need to use identical quantum emitters.
Applied Physics Letters, May 21, 2013
The Purcell effect dependence on the excitation power is studied in photonic crystal microcavity ... more The Purcell effect dependence on the excitation power is studied in photonic crystal microcavity lasers embedding InAs/InP quantum wires. In the case of non-lasing modes, the Purcell effect has low dependence on the optical pumping, attributable to an exciton dynamics combining free and localized excitons. In the case of lasing modes, the influence of the stimulated emission makes ambiguous the determination of the Purcell factor. We have found that this ambiguity can be avoided by measuring the dependence of the decay time on the excitation power. These results provide insights in the determination of the Purcell factor in microcavity lasers. V C 2013 AIP Publishing LLC.
Journal of the Optical Society of America B, Apr 18, 2013
We provide a methodology for the study of a photonic crystal microcavity and a quantum well (QW) ... more We provide a methodology for the study of a photonic crystal microcavity and a quantum well (QW) in the strong coupling regime by finite difference in the time domain. Numerical results for an InP L7 photonic crystal microcavity coupled to an ideal QW are provided. A comparison of the time analysis processed by the discrete Fourier transform, the Padé approximant, and harmonic inversion is presented to optimize the computation time. We present a method to solve the uncertainty of the frequency spectrum depending on the starting time used in the spectral analysis. The influence of polarization anisotropy on strong coupling is studied. The Rabi splitting is exactly zero only when the induced polarization in the QW is aligned with a field component incompatible with the symmetry of the mode.
Physical Review B, Aug 20, 2012
Single photon emission by an InAs/GaAs quantum dot weakly coupled to a photonic crystal microcavi... more Single photon emission by an InAs/GaAs quantum dot weakly coupled to a photonic crystal microcavity has been studied as a function of energy detuning. Precise and continuous control of the photon statistics as well as of the linear polarization emission angle is achieved simply by changing the energy detuning between the exciton and the cavity mode. A continuous decrease of the antibunching time, the bunching amplitude and the g 2 (0) value is observed as the detuning is decreased at constant excitation rate, due to the detuning-dependent Purcell effect.
Optics Express, Mar 21, 2012
The spontaneous emission rate and Purcell factor of selfassembled quantum wires embedded in photo... more The spontaneous emission rate and Purcell factor of selfassembled quantum wires embedded in photonic crystal micro-cavities are measured at 80 K by using micro-photoluminescence, under transient and steady state excitation conditions. The Purcell factors fall in the range 1.1 -2 despite the theoretical prediction of ≈15.5 for the figure of merit. We explain this difference by introducing a polarization dependence on the cavity orientation, parallel or perpendicular with respect to the wire axis, plus spectral and spatial detuning factors for the emitters and the cavity modes, taking in account the finite size of the quantum wires.
13th International Conference on Transparent Optical Networks (ICTON), 2011, Jun 2011
In this work we show two different procedures of fabrication aiming towards the systematic positi... more In this work we show two different procedures of fabrication aiming towards the systematic positioning of single InAs quantum dots (QDs) coupled to a GaAs photonic crystal (PC) microcavity. The two approaches are based on the molecular beam epitaxial (MBE) growth of site-controlled QDs (SCQDs) on pre-patterned structures. The PC microcavity (PCM) is introduced previous or after the growth, on each case. We demonstrate the InAs SCQD nucleation on pre-patterned PCMs and a method to perform the QD nucleation respect to an etched ruler that is used to position the PC structure after growth. For both types of structures, we have carried out microphotoluminescence (µPL) spectroscopy experiments at 80 K and 4 K.
Optics Express, Jun 7, 2010
We study the optical emission of single semiconductor quantum dots weakly coupled to a photonic-c... more We study the optical emission of single semiconductor quantum dots weakly coupled to a photonic-crystal micro-cavity. The linearly polarized emission of a selected quantum dot changes continuously its polarization angle, from nearly perpendicular to the cavity mode polarization at large detuning, to parallel at zero detuning, and reversing sign for negative detuning. The linear polarization rotation is qualitatively interpreted in terms of the detuning dependent mixing of the quantum dot and cavity states. The present result is relevant to achieve continuous control of the linear polarization in single photon emitters.
Journal of the Optical Society of America B, 2010
Photon correlation measurements on single InAs/ GaAs quantum rings embedded in a photonic crystal... more Photon correlation measurements on single InAs/ GaAs quantum rings embedded in a photonic crystal lattice demonstrate single-photon emission with g ͑2͒ ͑0͒ values of 0.4 and photon antibunching between the exciton and biexciton emissions. The measured photon antibunching times of the excitons are longer than that of the biexcitons, resulting in the time asymmetry of the exciton-biexciton photon cross-correlation. Phonon sidebands due to the piezoelectric coupling of excitons to acoustic phonons broaden the emission lines and shift them to lower energies at low excitation intensity.
Physical Review B, May 11, 2010
Long distance ͑1.4 m͒ interaction of two different InAs/GaAs quantum dots in a photonic crystal m... more Long distance ͑1.4 m͒ interaction of two different InAs/GaAs quantum dots in a photonic crystal microcavity is observed. Simultaneous coupling of both quantum dots to the cavity is demonstrated by Purcell effect measurements. Resonant optical excitation in the p state of any of the quantum dots, results in an increase in the s-state emission of the other one. The cavity-mediated coupling can be controlled by varying the excitation intensity. These results represent an experimental step toward the realization of quantum logic operations using distant solid-state qubits.
Raith Application Note, 2009
Optics Express, Aug 10, 2009
We present continuous wave laser emission in a photonic crystal microcavity operating at 1.5 μm a... more We present continuous wave laser emission in a photonic crystal microcavity operating at 1.5 μm at room temperature. The structures have been fabricated in an InP slab including a single layer of self-assembled InAs/InP quantum wires (QWrs) as active material. Laser emission in air suspended membranes with thresholds of effective optical pump power of 22 μW and quality factors up to 55000 have been measured.
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Publications by Ivan Prieto