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Book ; Online: A growth diagram for plasma-assisted molecular beam epitaxy of GaN nanocolumns on Si(111)

Fernández-Garrido, S. / Grandal, J. / Calleja, E. / Sánchez-García, M. A. / López-Romero, D.

2024

Abstract: The morphology of GaN samples grown by plasma-assisted molecular beam epitaxy on Si(111) was systematically studied as a function of impinging Ga/N flux ratio and growth temperature (750-850{\deg}C).Two different growth regimes were identified: compact ... ...

Abstract	The morphology of GaN samples grown by plasma-assisted molecular beam epitaxy on Si(111) was systematically studied as a function of impinging Ga/N flux ratio and growth temperature (750-850{\deg}C).Two different growth regimes were identified: compact and nanocolumnar. A growth diagram was established as a function of growth parameters, exhibiting the transition between growth regimes, and showing under which growth conditions GaN cannot be grown due to thermal decomposition and Ga desorption. Present results indicate that adatoms diffusion length and the actual Ga/N ratio on the growing surface are key factors to achieve nanocolumnar growth. Comment: This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in (citation of published article) and may be found at J. Appl. Phys. 106, 126102 (2009) and may be found at https://doi.org/10.1063/1.3267151
Keywords	Condensed Matter - Materials Science ; Physics - Applied Physics
Subject code	530
Publishing date	2024-01-29
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Structural and optical properties of self-assembled AlN nanowires grown on SiO2/Si substrates by molecular beam epitaxy

Gačević, Ž. / Grandal, J. / Guo, Q. / Kirste, R. / Varela, M. / Sitar, Z. / García, M. A. Sánchez

2024

Abstract: Self assembled AlN nanowires (NWs) are grown by plasma assisted molecular beam epitaxy (PAMBE) on SiO2 / Si (111) substrates. Using a combination of in-situ reflective high energy electron diffraction and ex situ X ray diffraction (XRD), we show that the ...

Abstract	Self assembled AlN nanowires (NWs) are grown by plasma assisted molecular beam epitaxy (PAMBE) on SiO2 / Si (111) substrates. Using a combination of in-situ reflective high energy electron diffraction and ex situ X ray diffraction (XRD), we show that the NWs grow nearly strain free, preferentially perpendicular to the amorphous SiO2 interlayer and without epitaxial relationship to Si(111) substrate, as expected. Scanning electron microscopy investigation reveals significant NWs coalescence, which results in their progressively increasing diameter and formation of columnar structures with non hexagonal cross section. Making use of scanning transmission electron microscopy (STEM), the NWs initial diameters are found in the 20 to 30 nm range. In addition, the formation of a thin (30 nm) polycrystalline AlN layer is observed on the substrate surface. Regarding the structural quality of the AlN NWs, STEM measurements reveal the formation of extended columnar regions, which grow with a virtually perfect metal-polarity wurtzite arrangement and with extended defects only sporadically observed. Combination of STEM and electron energy loss spectroscopy (EELS) reveals the formation of continuous aluminum oxide (1 to 2 nm) on the NW surface. Low temperature photoluminescence measurements reveal a single near band edge (NBE) emission peak, positioned at 6.03 eV (at 2 K), a value consistent with nearly zero NW strain evidenced by XRD and in agreement with the values obtained on AlN bulk layers synthesized by other growth techniques. The significant full width at half maximum of NBE emission, found at 20 meV (at 2 K), suggests that free and bound excitons are mixed together within this single emission band. Comment: 9 pages, 5 figures
Keywords	Condensed Matter - Materials Science ; Physics - Applied Physics
Subject code	530
Publishing date	2024-01-31
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Growth modes and coupled morphological-compositional modulations in GaP1-xNx layers grown on nominally (001)-oriented Si substrates

Saddik, K. Ben / Fernandez-Garrido, S. / Volkov, R. / Grandal, J. / Borgardt, N. / Garcia, B. J.

2023

Abstract: We investigated the chemical beam epitaxy of GaP1-xNx to correlate the growth parameters with their properties when they are grown on nominally (001)-oriented Si substrates, as desired for the lattice-matched integration of optoelectronic devices with ... ...

Abstract	We investigated the chemical beam epitaxy of GaP1-xNx to correlate the growth parameters with their properties when they are grown on nominally (001)-oriented Si substrates, as desired for the lattice-matched integration of optoelectronic devices with the standard Si technology. The growth mode as well as the chemical, morphological and structural properties of samples prepared using different growth temperatures and N precursor fluxes were analyzed by RHEED, XRD, RBS, NRA, EDX spectroscopy, AFM and TEM. Our results show that, up to x = 0.04, it is possible to synthesize smooth and chemically homogeneous GaP1-xNx layers with a high-structural quality in a 2D fashion, namely, layer-by-layer. For a given N mole fraction, the layer-by-layer growth mode is favored by lowering the growth temperature while decreasing the N precursor flux. As the flux of the N precursor is increased at a given temperature to enhance N incorporation, the quality of the layers degrades upon exceeding a temperature-dependent threshold; above this threshold, the growing layer experiences a growth mode transition from 2D to 3D after reaching a critical thickness of a few nm. Following that transition, the morphology and the chemical composition become modulated along the [110] direction with a period of several tens of nm. The surface morphology is then characterized by the formation of {113}-faceted wires, while the N concentration is enhanced at the troughs formed in between adjacent (113) and (-1-13) facets. We conclude on the feasibility of fabricating homogeneous thick GaP1-xNx layers lattice matched to Si (x = 0.021) or even with N content up to x=0.04. The possibility of exceeding a N mole fraction of 0.04 without inducing coupled morphological-compositional modulations has also been demonstrated when the layer thickness is kept below the critical value for the 2D-3D growth mode transition.
Keywords	Condensed Matter - Materials Science
Subject code	530
Publishing date	2023-02-02
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Structural and optical properties of self-assembled AlN nanowires grown on SiO

Gačević, Ž / Grandal, J / Guo, Q / Kirste, R / Varela, M / Sitar, Z / Sánchez García, M A

Nanotechnology

2021 Volume 32, Issue 19, Page(s) 195601

Abstract: Self-assembled AlN nanowires (NWs) are grown by plasma-assisted molecular beam epitaxy (PAMBE) on ... ...

Abstract	Self-assembled AlN nanowires (NWs) are grown by plasma-assisted molecular beam epitaxy (PAMBE) on SiO
Language	English
Publishing date	2021-02-11
Publishing country	England
Document type	Journal Article
ZDB-ID	1362365-5
ISSN	1361-6528 ; 0957-4484
ISSN (online)	1361-6528
ISSN	0957-4484
DOI	10.1088/1361-6528/abe2c7
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Article: Roles of Low Temperature Sputtered Indium Tin Oxide for Solar Photovoltaic Technology.

Fernández, Susana / González, José Pablo / Grandal, Javier / Braña, Alejandro F / Gómez-Mancebo, María Belén / Gandía, José Javier

Materials (Basel, Switzerland)

2021 Volume 14, Issue 24

Abstract: Different functionalities of materials based on indium tin oxide and fabricated at soft conditions were investigated with the goal of being used in a next generation of solar photovoltaic devices. These thin films were fabricated in a commercial UNIVEX ... ...

Abstract	Different functionalities of materials based on indium tin oxide and fabricated at soft conditions were investigated with the goal of being used in a next generation of solar photovoltaic devices. These thin films were fabricated in a commercial UNIVEX 450B magnetron sputtering. The first studied functionality consisted of an effective n-type doped layer in an n-p heterojunction based on p-type crystalline silicon. At this point, the impact of the ITO film thickness (varied from 45 to 140 nm) and the substrate temperature (varied from room temperature to 250 °C) on the heterojunction parameters was evaluated separately. To avoid possible damages in the heterojunction interface, the applied ITO power was purposely set as low as 25 W; and to minimize the energy consumption, no heat treatment process was used. The second functionality consisted of indium-saving transparent conductive multicomponent materials for full spectrum applications. This was carried out by the doping of the ITO matrix with transition metals, as titanium and zinc. This action can reduce the production cost without sacrificing the optoelectronic film properties. The morphology, chemical, structural nature and optoelectronic properties were evaluated as function of the doping concentrations. The results revealed low manufactured and suitable films used successfully as conventional emitter, and near-infrared extended transparent conductive materials with superior performance that conventional ones, useful for full spectrum applications. Both can open interesting choices for cost-effective photovoltaic technologies.
Language	English
Publishing date	2021-12-15
Publishing country	Switzerland
Document type	Journal Article
ZDB-ID	2487261-1
ISSN	1996-1944
ISSN	1996-1944
DOI	10.3390/ma14247758
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Book ; Online: Effect of different buffer layers on the quality of InGaN layers grown on Si

Gómez, V. J. / Grandal, J. / Núñez-Cascajero, A. / Naranjo, F. B. / Varela, M. / Sánchez-García, M. A. / Calleja, E.

2019

Abstract: This work studies the effect of four different types of buffer layers on the structural and optical properties of InGaN layers grown on Si(111) substrates and their correlation with electrical characteristics. The vertical electrical conduction of n- ... ...

Abstract	This work studies the effect of four different types of buffer layers on the structural and optical properties of InGaN layers grown on Si(111) substrates and their correlation with electrical characteristics. The vertical electrical conduction of n-InGaN/buffer-layer/p-Si heterostructures, with In composition near 46%, which theoretically produces an alignment of the bands, is analyzed. Droplet elimination by radical-beam irradiation was successfully applied to grow high quality InGaN films on Si substrates for the first time. Among several buffer choices, an AlN buffer layer with a thickness above 24 nm improves the structural and optical quality of the InGaN epilayer while keeping a top to bottom ohmic behavior. These results will allow fabricating double-junction InGaN/Si solar cells without the need of tunnel junctions between the two sub-cells, therefore simplifying the device design.
Keywords	Physics - Applied Physics ; Condensed Matter - Materials Science
Subject code	530 ; 620
Publishing date	2019-08-29
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Quasiparticle tunnel electroresistance in superconducting junctions.

Rouco, V / Hage, R El / Sander, A / Grandal, J / Seurre, K / Palermo, X / Briatico, J / Collin, S / Trastoy, J / Bouzehouane, K / Buzdin, A I / Singh, G / Bergeal, N / Feuillet-Palma, C / Lesueur, J / Leon, C / Varela, M / Santamaría, J / Villegas, Javier E

Nature communications

2020 Volume 11, Issue 1, Page(s) 658

Abstract: The term tunnel electroresistance (TER) denotes a fast, non-volatile, reversible resistance switching triggered by voltage pulses in ferroelectric tunnel junctions. It is explained by subtle mechanisms connected to the voltage-induced reversal of the ... ...

Abstract	The term tunnel electroresistance (TER) denotes a fast, non-volatile, reversible resistance switching triggered by voltage pulses in ferroelectric tunnel junctions. It is explained by subtle mechanisms connected to the voltage-induced reversal of the ferroelectric polarization. Here we demonstrate that effects functionally indistinguishable from the TER can be produced in a simpler junction scheme-a direct contact between a metal and an oxide-through a different mechanism: a reversible redox reaction that modifies the oxide's ground-state. This is shown in junctions based on a cuprate superconductor, whose ground-state is sensitive to the oxygen stoichiometry and can be tracked in operando via changes in the conductance spectra. Furthermore, we find that electrochemistry is the governing mechanism even if a ferroelectric is placed between the metal and the oxide. Finally, we extend the concept of electroresistance to the tunnelling of superconducting quasiparticles, for which the switching effects are much stronger than for normal electrons. Besides providing crucial understanding, our results provide a basis for non-volatile Josephson memory devices.
Language	English
Publishing date	2020-01-31
Publishing country	England
Document type	Journal Article
ZDB-ID	2553671-0
ISSN	2041-1723 ; 2041-1723
ISSN (online)	2041-1723
ISSN	2041-1723
DOI	10.1038/s41467-020-14379-w
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Article ; Online: Magnetization process of a ferromagnetic nanostrip under the influence of a surface acoustic wave.

Castilla, David / Yanes, Rocío / Sinusía, Miguel / Fuentes, Gonzalo / Grandal, Javier / Maicas, Marco / Álvarez-Arenas, Tomás E G / Muñoz, Manuel / Torres, Luis / López, Luis / Prieto, José L

Scientific reports

2020 Volume 10, Issue 1, Page(s) 9413

Abstract: Surface Acoustic Waves (SAW) are one of the possible solutions to target the challenges faced by modern spintronic devices. The stress carried by the SAW can decrease the current required to achieve magnetic switching or domain wall movement by spin ... ...

Abstract	Surface Acoustic Waves (SAW) are one of the possible solutions to target the challenges faced by modern spintronic devices. The stress carried by the SAW can decrease the current required to achieve magnetic switching or domain wall movement by spin transfer torque. Although the last decade has produced very relevant results in this field, it is still important to study the effects of a SAW on the basic unit of many spintronic devices, a ferromagnetic nanostrip. In this work, we perform a complete set of measurements and simulations to characterize the magnetization process of a Ni nanostrip under the influence of a SAW. We find that the SAW increases the mobility and the depinning ability of the magnetic domain walls and consequently, promotes a sharper approach to saturation and substantially decreases coercivity. We have also found other two interesting effects. When the SAW has sufficient energy, is able to trigger irreversible transitions even before switching the direction of the external magnetic field. Additionally, we have found that the magnetization process depends on the direction of the travelling SAW.
Language	English
Publishing date	2020-06-10
Publishing country	England
Document type	Journal Article
ZDB-ID	2615211-3
ISSN	2045-2322 ; 2045-2322
ISSN (online)	2045-2322
ISSN	2045-2322
DOI	10.1038/s41598-020-66144-0
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Article ; Online: Coaxial multishell (In,Ga)As/GaAs nanowires for near-infrared emission on Si substrates.

Dimakis, Emmanouil / Jahn, Uwe / Ramsteiner, Manfred / Tahraoui, Abbes / Grandal, Javier / Kong, Xiang / Marquardt, Oliver / Trampert, Achim / Riechert, Henning / Geelhaar, Lutz

Nano letters

2014 Volume 14, Issue 5, Page(s) 2604–2609

Abstract: Efficient infrared light emitters integrated on the mature Si technology platform could lead to on-chip optical interconnects as deemed necessary for future generations of ultrafast processors as well as to nanoanalytical functionality. Toward this goal, ...

Abstract	Efficient infrared light emitters integrated on the mature Si technology platform could lead to on-chip optical interconnects as deemed necessary for future generations of ultrafast processors as well as to nanoanalytical functionality. Toward this goal, we demonstrate the use of GaAs-based nanowires as building blocks for the emission of light with micrometer wavelength that are monolithically integrated on Si substrates. Free-standing (In,Ga)As/GaAs coaxial multishell nanowires were grown catalyst-free on Si(111) by molecular beam epitaxy. The emission properties of single radial quantum wells were studied by cathodoluminescence spectroscopy and correlated with the growth kinetics. Controlling the surface diffusivity of In adatoms along the NW side-walls, we improved the spatial homogeneity of the chemical composition along the nanowire axis and thus obtained a narrow emission spectrum. Finally, we fabricated a light-emitting diode consisting of approximately 10(5) nanowires contacted in parallel through the Si substrate. Room-temperature electroluminescence at 985 nm was demonstrated, proving the great potential of this technology.
Language	English
Publishing date	2014-04-01
Publishing country	United States
Document type	Journal Article
ISSN	1530-6992
ISSN (online)	1530-6992
DOI	10.1021/nl500428v
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Article ; Online: Investigation of III-V nanowires by plan-view transmission electron microscopy: InN case study.

Luna, Esperanza / Grandal, Javier / Gallardo, Eva / Calleja, José M / Sánchez-García, Miguel Á / Calleja, Enrique / Trampert, Achim

Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada

2014 Volume 20, Issue 5, Page(s) 1471–1478

Abstract: We discuss observations of InN nanowires (NWs) by plan-view high-resolution transmission electron microscopy (TEM). The main difficulties arise from suitable methods available for plan-view specimen preparation. We explore different approaches and find ... ...

Abstract	We discuss observations of InN nanowires (NWs) by plan-view high-resolution transmission electron microscopy (TEM). The main difficulties arise from suitable methods available for plan-view specimen preparation. We explore different approaches and find that the best results are obtained using a refined preparation method based on the conventional procedure for plan-view TEM of thin films, specifically modified for the NW morphology. The fundamental aspects of such a preparation are the initial mechanical stabilization of the NWs and the minimization of the ion-milling process after dimpling the samples until perforation. The combined analysis by plan-view and cross-sectional TEM of the NWs allows determination of the degree of strain relaxation and reveals the formation of an unintentional shell layer (2-3-nm thick) around the InN NWs. The shell layer is composed of bcc In2O3 nanocrystals with a preferred orientation with respect to the wurtzite InN: In2O3 [111] \|\| InN [0001] and In2O3<110>\|\|InN<1120>.
MeSH term(s)	Indium ; Microscopy, Electron, Transmission ; Nanowires/chemistry ; Nanowires/ultrastructure
Chemical Substances	Indium (045A6V3VFX) ; indium nitride (D66UAC005A)
Language	English
Publishing date	2014-10
Publishing country	United States
Document type	Journal Article
ZDB-ID	1385710-1
ISSN	1435-8115 ; 1431-9276
ISSN (online)	1435-8115
ISSN	1431-9276
DOI	10.1017/S1431927614013038
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