Multi-technique characterisation of MOVPE-grown GaAs on Si

The heterogeneous integration of III-V materials on a Si CMOS platform offers tremendous prospects for future high speed and low power logic applications. That said this integration generates immense scientific and technological challenges. In this work multi-technique characterisation is used to investigate properties of GaAs layers grown by Metal-Organic Vapour Phase Epitaxy (MOVPE) on Si substrates - (100) with 4⁰ offset towards - under various growth conditions. This being a crucial first step towards the production of III-V template layers with a relatively lower density of defects for selective epitaxial overgrowth of device quality material. The optical and structural properties of heteroepitaxial GaAs are first investigated by micro-Raman spectroscopy and photoluminescence and reflectance measurements. High-resolution X-ray diffraction (HR-XRD) is used to investigate structural properties. Advanced XRD techniques, including double-axis diffraction and X-ray crystallographic mapping are used to evaluate degrees of relaxation and distribution of the grain orientations in the epilayers, respectively. Results obtained from the different methodologies are compared in an attempt to understand growth kinetics of the materials system. The GaAs overlayer grown with annealing at 735⁰C following As predeposition at 500⁰C shows the best crystallinity. Close inspection confirms the growth of epitaxial GaAs preferentially oriented along (100) embedded in a highly-textured polycrystalline structure

Reflectance anisotropy spectroscopy assessment of the MOVPE nucleation of GaInP on Germanium (100)

This work summarizes the observations made on the variation and time evolution of the reflectanceanisotropy signal during the MOVPE growth of GaInPnucleation layers on Germanium substrates. This in situ monitoring tool is used to assess the impact of different nucleation routines and reactor conditions on the quality of the layers grown. This comparison is carried out by establishing a correlation between reflectanceanisotropy signature at 2.1 eV and the morphology of the epilayers evaluated by atomic force microscopy (AFM). This paper outlines the potential of reflectanceanisotropy to predict, explore, and therefore optimize, the best growth conditions that lead to a high quality III–V epilayer on a Ge substrat

Structural investigation of MOVPE-Grown GaAs on Ge by X-ray techniques

The selection of appropriate characterisation methodologies is vital for analysing and comprehending the sources of defects and their influence on the properties of heteroepitaxially grown III-V layers. In this work we investigate the structural properties of GaAs layers grown by Metal-Organic Vapour Phase Epitaxy (MOVPE) on Ge substrates – (100) with 6⁰ offset towards – under various growth conditions. Synchrotron X-ray topography (SXRT) is employed to investigate the nature of extended linear defects formed in GaAs epilayers. Other X-ray techniques, such as reciprocal space mapping (RSM) and triple axis ω-scans of (00l)-reflections (l = 2, 4, 6) are used to quantify the degree of relaxation and presence of antiphase domains (APDs) in the GaAs crystals. The surface roughness is found to be closely related to the size of APDs formed at the GaAs/Ge heterointerface, as confirmed by X-ray diffraction (XRD), as well as atomic force microscopy (AFM), and transmission electron microscopy (TEM)

Structural investigation of MOVPE-Grown GaAs on Ge by X-ray techniques

The selection of appropriate characterisation methodologies is vital for analysing and comprehending the sources of defects and their influence on the properties of heteroepitaxially grown III-V layers. In this work we investigate the structural properties of GaAs layers grown by Metal-Organic Vapour Phase Epitaxy (MOVPE) on Ge substrates – (100) with 6⁰ offset towards – under various growth conditions. Synchrotron X-ray topography (SXRT) is employed to investigate the nature of extended linear defects formed in GaAs epilayers. Other X-ray techniques, such as reciprocal space mapping (RSM) and triple axis ω-scans of (00l)-reflections (l = 2, 4, 6) are used to quantify the degree of relaxation and presence of antiphase domains (APDs) in the GaAs crystals. The surface roughness is found to be closely related to the size of APDs formed at the GaAs/Ge heterointerface, as confirmed by X-ray diffraction (XRD), as well as atomic force microscopy (AFM), and transmission electron microscopy (TEM)

High quality optically active and integrable EuOOH films prepared by pulsed laser deposition

Rare-earth (RE)-Oxygen-Hydrogen compounds are versatile materials whose composition and properties can be significantly varied by changing the relative O and H contents. Among them hydrides and oxyhydrides have been thoroughly investigated due to its photochromic properties. Instead, research of RE-hydroxides and oxyhydroxides (RE-OH and RE-OOH) is scarce although they show promising properties as light emitters. However, their use and integration in solid state devices have been hindered so far because their usual chemical synthesis routes yield materials in bulk or powder configurations. In this work we demonstrate a physical deposition route based on pulsed laser deposition that results in the unprecedented preparation of high-quality Eu oxyhydroxide (EuOOH) thin films. The synthetized EuOOH films show a well-defined monoclinic structure, are optically active and show a robust red emission related to the intra-f transitions of the Eu3+ ions. The excellent quality of these crystalline films has allowed us to obtain relevant properties of the monoclinic EuOOH phase not previously reported such as its refractive index and its Raman spectrum, including the identification of the characteristic phonon modes. These novel EuOOH films have been prepared both on Si and fused silica substrates, and thus are ready for potential integration in solid state optoelectronic components and devicesThis work was funded by the Spanish Research Agency (AEI, Ministry of Research and Innovation) and the European Regional Development Fund (ERDF) under grants RTI2018-096498-B-I00, RTI2018-101020-B-I00, RTI2018-096918-B-C41 and PID2021-123190OB-I00; by the CSIC (PIE-202050E195 and project 2021AEP128IO); by the Regional Government of Madrid through TECHNOFUSION(III)CM ´ (S2018/EMT-4437); and by Comunidad de Madrid (Spain) multiannual agreement with UC3M, “Excelencia para el Profesorado Universitario” (EPUC3M14) - Fifth regional research plan 2016-2020. The work of A. Cano was partially supported by the Autonomous Community of Madrid and the European Social Fund (PEJD-2019-PRE/TIC-16082

Tuning the size, composition and structure of Au and Co50Au50 Nanoparticles by High-Power Impulse Magnetron Sputtering in gas-phase Synthesis

Gas-phase synthesis of nanoparticles with different structural and chemical distribution is reported using a circular magnetron sputtering in an ion cluster source by applying high-power impulses. The influence of the pulse characteristics on the final deposit was evaluated on Au nanoparticles. The results have been compared with the more common direct current approach. In addition, it is shown for the first time that high-power impulses in magnetron based gas aggregation sources allows the growth of binary nanoparticles, CoAu in this case, with a variety of crystalline and chemical arrangements which are analyzed at the atomic level

Cathodoluminescence Characterization of Dilute Nitride GaNSbAs Alloys

The effects of ex situ annealing in N ambient and in situ annealing in As ambient on GaNSbAs/GaAs structures grown by molecular beam epitaxy were investigated by low temperature cross-sectional cathodoluminescence (CL). The amount and distribution of Sb was measured by energy dispersive spectroscopy (EDS). The cross-sectional CL analysis of all samples reveals a shift of the near band edge (NBE) emission along the growth axis, presumably associated with a non-uniform incorporation of Sb during the growth process, in agreement with the Sb distribution measured by EDS in the as-grown sample. The NBE emission in the annealed samples presents a redshift with respect to the as-grown sample. This effect might be explained by a redistribution/activation of N in the GaNSbAs lattice since the Sb distribution measured by EDS does not reveal significant changes, within the error margin, with respect to the as-grown sample. The in situ annealed in the As overpressure sample shows the best properties for solar cells applications, i.e., a NBE peak position close to 1.0 eV and the lowest full width at half maximum of this emission.Spanish Government (MINECO Project ENE2014- 56069-C4-4-R) and Junta de Castilla y Leo´n (VA293U13 and VA081U16 Projects). The Ministry of Economy and Competitiveness MINECO supports this work through Projects TEC2014-54260- C3-1-P, TEC2014-54260-C3-2-P, TEC2014-54260- C3-3-P, PCIN-2015-181-C02-01 and PCIN-2015- 181-C02-02

The marine fish food web is globally connected

The productivity of marine ecosystems and the services they provide to humans are largely dependent on complex interactions between prey and predators. These are embedded in a diverse network of trophic interactions, resulting in a cascade of events following perturbations such as species extinction. The sheer scale of oceans, however, precludes the characterization of marine feeding networks through de novo sampling. This effort ought instead to rely on a combination of extensive data and inference. Here we investigate how the distribution of trophic interactions at the global scale shapes the marine fish food web structure. We hypothesize that the heterogeneous distribution of species ranges in biogeographic regions should concentrate interactions in the warmest areas and within species groups. We find that the inferred global metaweb of marine fish—that is, all possible potential feeding links between co-occurring species—is highly connected geographically with a low degree of spatial modularity. Metrics of network structure correlate with sea surface temperature and tend to peak towards the tropics. In contrast to open-water communities, coastal food webs have greater interaction redundancy, which may confer robustness to species extinction. Our results suggest that marine ecosystems are connected yet display some resistance to perturbations because of high robustness at most locations.Using a global interaction dataset, the authors quantify the distribution of trophic interactions among marine fish, finding a high degree of geographic connectivity but low spatial modularity.C.A. was supported by a MELS-FQRNT Postdoctoral Fellowship and a Ressources Aquatique Québec (RAQ) fellowship during the conception and writing of this manuscript. T.P., D.G. and D.B.S. acknowledge financial support by the CIEE through their working group programme. M.B.A. is funded through FCT project No. PTDC/AAG-MAA/3764/2014. A.R.C. is funded by a Natural Sciences and Engineering Research Council of Canada (NSERC) PGS-D scholarship. D.G., T.P., M.-J.F., P.A. and S.J.L. are supported by NSERC Discovery Grants. T.P. also acknowledges a FRQNT New Investigator award and a Université de Montréal starting grant. D.B.S. acknowledges support from the Royal Society of New Zealand (via Marsden Fast-Start No. UOC-1101 and a Rutherford Discovery Fellowship)

Advanced transmission electron microscopy investigation of defect formation in movpe-growth of gap on silicon using arsenic initial coverage

Integration of GaP layers on silicon substrates using AsH3 pre-exposure followed by a PH3-based GaP epitaxial growth allows the development of very promising processes for the photovoltaic industry, although many of the growth routines using this approach suffer from reproducibility issues when transferred to a new epitaxial system, leading to poor quality layers. This fact reveals a lack of knowledge on the mechanisms behind the formation of the most common planar defects (stacking faults and microtwins) and their dynamics for GaP/Si Metal Organic Vapor Phase Epitaxy using AsH3 and PH3. Therefore, in this work, a set of GaP/Si samples with a similarly high defect density grown between 700 °C and 725 °C, are analyzed by means of high-resolution scanning transmission electron microscopy and electron energy loss spectroscopy. The results presented show contaminant-free Si surfaces for temperatures above 725 °C, ruling out the hypothesis of contaminant as the origin of these planar defects. Regarding the interface Si/GaP, the GaP growth starts, in all the samples, with Ga Si bonds. Additionally, no traces of As are found, which reinforces the hypothesis of an effectively displacement of As on Si surface by Ga atoms at high temperature. Finally, it is observed complex chemical structures in the origin of the microtwins and the cause of the origin of these defects seems to be a localized gallium depletion at the GaP/Si interface