arXiv subjects

Gilles Patriarche

Publications and source records attributed to Gilles Patriarche.

31 records · Page 2Linked to original sources

arXiv2020

Highly Ordered Boron Nitride/Epigraphene Epitaxial Films on Silicon Carbide by Lateral Epitaxial Deposition

Realizing high-performance nanoelectronics requires control of materials at the nanoscale. Methods to produce high quality epitaxial graphene (EG) nanostructures on silicon carbide are known. The next step is to grow Van der Waals semiconductors on top of EG nanostructures. Hexagonal boron nitride (h-BN) is a wide bandgap semiconductor with a honeycomb lattice structure that matches that of graphene, making it ideally suited for graphene-based nanoelectronics. Here, we describe the preparation and characterization of multilayer h-BN grown epitaxially on EG using a migration-enhanced metalorganic vapor phase epitaxy process. As a result of the lateral epitaxial deposition (LED) mechanism, the grown h-BN/EG heterostructures have highly ordered epitaxial interfaces, as desired in order to preserve the transport properties of pristine graphene. Atomic scale structural and energetic details of the observed row-by-row, growth mechanism of the 2D epitaxial h-BN film are analyzed through first-principles simulations, demonstrating one-dimensional nucleation-free-energy-barrierless growth. This industrially relevant LED process can be applied to a wide variety of van der Waals materials.

cond-mat.mtrl-sci↗

arXiv2020

Experimental quantification of atomically-resolved HAADF-STEMimages using EDX

Atomically-resolved mappings of the indium composition in InGaN/GaN multi-quantum wellstructures have been obtained by quantifying the contrast in HAADF-STEM. The quantificationprocedure presented here does not rely on computation-intensive simulations, but rather uses EDXmeasurements to calibrate the HAADF-STEM contrast. The histogram of indium compositionsobtained from the mapping provides unique insights into the growth of InGaN: the transitionfrom GaN to InGaN and vice versa occurs in discreet increments of composition; each incrementcorresponds to one monolayer of the interface, indicating that nucleation takes longer than thelateral growth of the step. Strain-state analysis is also performed by applying Peak-Pair Analysisto the positions of the atomic columns identified the quantification of the contrast. The strainmappings yield an estimate of the composition in good agreement with the one obtained fromquantified HAADF-STEM, albeit with a lower precision. Possible improvements to increase theprecision of the strain mappings are discussed, opening potential pathways for the quantification ofarbitrary quaternary alloys at atomic scales.

cond-mat.mtrl-sci↗

arXiv2019

InAs quantum dot in a needlelike tapered InP nanowire: a telecom band single photon source monolithically grown on silicon

Realizing single photon sources emitting in the telecom band on silicon substrates is essential to reach complementary-metal-oxide-semiconductor (CMOS) compatible devices that secure communications over long distances. In this work, we propose the monolithic growth of needlelike tapered InAs/InP quantum dot-nanowires (QD-NWs) on silicon substrates with a small taper angle and a nanowire diameter tailored to support a single mode waveguide. Such a NW geometry is obtained by a controlled balance over axial and radial growths during the gold-catalyzed growth of the NWs by molecular beam epitaxy. This allows us to investigate the impact of the taper angle on the emission properties of a single InAs/InP QD-NW. At room temperature, a Gaussian far-field emission profile in the telecom O-band with a 30° beam divergence angle is demonstrated from a single InAs QD embedded in a 2° tapered InP NW. Moreover, single photon emission is observed at cryogenic temperature for an off-resonant excitation and the best result, $g^2(0) = 0.05$, is obtained for a 7° tapered NW. This all-encompassing study paves the way for the monolithic growth on silicon of an efficient single photon source in the telecom band based on InAs/InP QD-NWs.

physics.app-ph↗

arXiv2019

Single-electron tunneling PbS/InP neuromorphic computing building blocks

We study single-electron tunneling (SET) characteristics in crystalline PbS/InP junctions, that exhibit single-electron Coulomb-blockade staircases along with memory and memory-fading behaviors. This gives rise to both short-term and long-term plasticities as well as a convenient non-linear response, making this structure attractive for neuromorphic computing applications. For further insights into this prospect, we predict typical behaviors relevant to the field, obtained by an extrapolation of experimental data in the SET framework. The estimated minimum energy required for a synaptic operation is in the order of 1 fJ, while the maximum frequency of operation can reach the MHz range.

physics.app-ph↗

arXiv2016

Interplay between tightly focused excitation and ballistic propagation of polariton condensates in a ZnO microcavity

The formation and propagation of a polariton condensate under tightly focused excitation is investigated in a ZnO microcavity both experimentally and theoretically. 2D near-field and far-field images of the condensate are measured under quasi-continuous non-resonant excitation. The corresponding spatial profiles are compared to a model based on the Gross-Pitaevskii equation under cylindrical geometry. This work allows to connect the experiments performed with a small excitation laser spot and the previous kinetic models of condensation in a 2D infinite microcavity, and to determine the relevant parameters of both the interaction and the relaxation between the reservoir and the condensate. Two main parameters are identified: the exciton-photon detuning through the polariton effective mass and the temperature, which determines the efficiency of the relaxation from the reservoir to the condensate.

cond-mat.mes-hall↗

arXiv2015

Nano selective area growth of GaN by MOVPE on 4H-SiC using epitaxial graphene as a mask: towards integrated III-nitride / graphene / SiC electronics and optoelectronics

We report the growth of high-quality triangular GaN nanomesas, 30-nm thick, on the C-face of 4H-SiC using nano selective area growth (NSAG) with patterned epitaxial graphene grown on SiC as an embedded mask. NSAG alleviates the problems of defective crystals in the heteroepitaxial growth of nitrides, and the high mobility graphene film can readily provide the back low-dissipative electrode in GaN-based optoelectronic devices. The process consists in first growing a 5-8 graphene layers film on the C-face of 4H- SiC by confinement-controlled sublimation of silicon carbide. The graphene film is then patterned and arrays of 75-nanometer-wide openings are etched in graphene revealing the SiC substrate. 30-nanometer-thick GaN is subsequently grown by metal organic vapor phase epitaxy. GaN nanomesas grow epitaxially with perfect selectivity on SiC, in openings patterned through graphene, with no nucleation on graphene. The up-or-down orientation of the mesas on SiC, their triangular faceting, and cross-sectional scanning transmission electron microscopy show that they are biphasic. The core is a zinc blende monocrystal surrounded with single-crystal hexagonal wurtzite. The GaN crystalline nanomesas have no threading dislocations, and do not show any V-pit. This NSAG process potentially leads to integration of high-quality III-nitrides on the wafer scalable epitaxial graphene / silicon carbide platform.

cond-mat.mtrl-sci↗

arXiv2012

Conductance statistics from a large array of sub-10 nm molecular junctions

Devices made of few molecules constitute the miniaturization limit that both inorganic and organic-based electronics aspire to reach. However, integration of millions of molecular junctions with less than 100 molecules each has been a long technological challenge requiring well controlled nanometric electrodes. Here we report molecular junctions fabricated on a large array of sub-10 nm single crystal Au nanodots electrodes, a new approach that allows us to measure the conductance of up to a million of junctions in a single conducting Atomic Force Microscope (C-AFM) image. We observe two peaks of conductance for alkylthiol molecules. Tunneling decay constant (beta) for alkanethiols, is in the same range as previous studies. Energy position of molecular orbitals, obtained by transient voltage spectroscopy, varies from peak to peak, in correlation with conductance values.

cond-mat.mes-hall↗

arXiv2011

Quasi one-dimensional transport in single GaAs/AlGaAs core-shell nanowires

We present an original approach to fabricate single GaAs/AlGaAs core-shell nanowire with robust and reproducible transport properties. The core-shell structure is buried in an insulating GaAs overlayer and connected as grown in a two probe set-up using the highly doped growth substrate and a top diffused contact. The measured conductance shows a non-ohmic behavior with temperature and voltage-bias dependences following power laws, as expected for a quasi-1D system.

cond-mat.mtrl-sci↗

arXiv2010

Quantum well infrared photodetectors hardiness to the non ideality of the energy band profile

We report results on the effect of a non-sharp and disordered potential in Quantum Well Infrared Photodetectors (QWIP). Scanning electronic transmission microscopy is used to measure the alloy profile of the structure which is shown to present a gradient of composition along the growth axis. Those measurements are used as inputs to quantify the effect on the detector performance (peak wavelength, spectral broadening and dark current). The influence of the random positioning of the doping is also studied. Finally we demonstrate that QWIP properties are quite robust with regard to the non ideality of the energy band profile.

cond-mat.mes-hall↗

arXiv2009

Interface roughness transport in THz quantum cascade detectors

Infrared Detectors based on a Quantum Cascade have been proposed to suppress the dark current which is identified as a limiting factor in Quantum Well Infrared Photodetectors. Those detectors have been mostly designed for the 3-5um and 8-12um range of wavelength. For detector operating in the THz range a complete change of regime of transport is expected since the photon energy is lower than the Longitudinal Optical (LO) phonon energy. Using a two dimensional code of transport we have identified Interface Roughness (IR) as the key interaction in such a structure. We have used scanning transmission electron microscopy (STEM) to evaluate the IR parameters (magnitude of the roughness and mean distance between defects) instead of the classical mobility measurements. Finally, we used these parameters to study their influence on the resistance of the device.

cond-mat.mes-hall↗

arXiv2006

Magnetic properties and domain structure of (Ga,Mn)As films with perpendicular anisotropy

The ferromagnetism of a thin GaMnAs layer with a perpendicular easy anisotropy axis is investigated by means of several techniques, that yield a consistent set of data on the magnetic properties and the domain structure of this diluted ferromagnetic semiconductor. The magnetic layer was grown under tensile strain on a relaxed GaInAs buffer layer using a procedure that limits the density of threading dislocations. Magnetometry, magneto-transport and polar magneto-optical Kerr effect (PMOKE) measurements reveal the high quality of this layer, in particular through its high Curie temperature (130 K) and well-defined magnetic anisotropy. We show that magnetization reversal is initiated from a limited number of nucleation centers and develops by easy domain wall propagation. Furthermore, MOKE microscopy allowed us to characterize in detail the magnetic domain structure. In particular we show that domain shape and wall motion are very sensitive to some defects, which prevents a periodic arrangement of the domains. We ascribed these defects to threading dislocations emerging in the magnetic layer, inherent to the growth mode on a relaxed buffer.

cond-mat.mtrl-sci↗

arXiv2004

Long-range ordering of III-V semiconductor nanostructures by shallowly buried dislocation networks

We account for lateral orderings of III-V nanostructures resulting from a GaAs/InAs/InGaAs/GaAs sequence grown on GaAs by metallorganic vapour phase epitaxy at two different temperatures. For both samples, the ordering is induced by the stress field of a periodic dislocation network (DN) shallowly buried and parallel to the surface. This DN is a grain boundary (GB) that forms, between a thinGaAs layer (onwhich growthwas performed) and aGaAs substrate joined together by wafer bonding, in order to accommodate a tilt and a twist between these two crystals; both these misorientations are imposed in a controlled manner. This GB is composed of a one-dimensional network of mixed dislocations and of a one-dimensional network of screwdislocations. For both samples, the nanostructures observed by transmission electronmicroscopy (TEM) and atomic forcemicroscopy are ordered by the underlyingDNobserved byTEMsince they have same dimensions andorientations as the cells of the DN.

cond-mat.mtrl-sci↗

arXiv2004

Buried dislocation networks designed to organize the growth of III-V semiconductor nanostructures

We first report a detailed transmission electron microscopy study of dislocation networks (DNs) formed at shallowly buried interfaces obtained by bonding two GaAs crystals between which we establish in a controlled manner a twist and a tilt around a k110l direction. For large enough twists, the DN consists of a twodimensional network of screw dislocations accommodating mainly the twist and of a one-dimensional network of mixed dislocations accommodating mainly the tilt. We show that in addition the mixed dislocations accommodate part of the twist and we observe and explain slight unexpected disorientations of the screw dislocations with respect to the k110l directions. By performing a quantitative analysis of the whole DN, we propose a coherent interpretation of these observations which also provides data inaccessible by direct experiments. When the twist is small enough, one screw subnetwork vanishes. The surface strain field induced by such DNs has been used to pilot the lateral ordering of GaAs and InGaAs nanostructures during metal-organic vapor phase epitaxy. We prove that the dimensions and orientations of the nanostructures are correlated with those of the cells of the underlying DN and explain how the interface dislocation structure governs the formation of the nanostructures.

cond-mat.mtrl-sci↗