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Quaternary alloys enable the independent optimization of different semiconductor properties, such as the separate tuning of the band gap and the lattice constant. Nanowire core-shell structures should allow a larger range of compositional tuning as strain can be accommodated in a more effective manner than in thin films. Still, the faceted structure of the nanowire may lead to local segregation effects. Here, we explore the incorporation of indium in AlGaAs shells up to 25%. In particular, we show the effect of In incorporation on the energy shift of the AlGaInAs single-photon emitters present in the shell. We observe a redshift up to 300 meV as a function of the group-III site fraction of In. We correlate the shift with segregation at the nanoscale. We find evidence of the segregation of the group-III elements at different positions in the nanowire, not observed before. We propose a model that takes into account the strain distribution in the nanowire shell and the adatom diffusion on the nanowire facets to explain the observations. This work provides novel insights on the segregation phenomena necessary to engineer the composition of multidinary alloys. ; JSR thanks the European H2020 for funding through grant LIMQUET. EDR and LR thank Labex EMC3 AQURATE (French ANR). SMS acknowledges funding from "Programa Internacional de Becas 'la Caixa'-Severo Ochoa." JA and SMS acknowledge funding from Generalitat de Catalunya 2017 SGR 327 and the Spanish MINECO project ENE2017-85087-C3. ICN2 acknowledges support from the Severo Ochoa Programme (MINECO, Grant No. SEV-2013-0295) and is funded by the CERCA Programme / Generalitat de Catalunya. Part of the present work has been performed in the framework of Universitat Autònoma de Barcelona Materials Science PhD program. This work has received funding from the European Union's Horizon 2020 Research and Innovation Programme under grant agreement No. 654360 NFFA-Europe. ; Peer reviewed

IMN acknowledge funding from the European Union FEDER, FSE. EURAMET EMPIR 17FUN06 SIQUST. SMS acknowledges funding from "Programa Internacional de Becas 'la Caixa'-Severo Ochoa". ICN2 is funded by the CERCA Programme/Generalitat de Catalunya. Part of the present work has been performed in the framework of Universitat Autònoma de Barcelona Materials Science PhD program. Part of the HAADF-STEM microscopy was conducted in the Laboratorio de Microscopias Avanzadas at Instituto de Nanociencia de Aragon-Universidad de Zaragoza. We acknowledge support from CSIC Research Platform on Quantum Technologies PTI-001. ; The growth of compound semiconductors on silicon has been widely sought after for decades, but reliable methods for defect-free combination of these materials have remained elusive. Recently, interconnected GaAs nanoscale membranes have been used as templates for the scalable integration of nanowire networks on III-V substrates. Here, we demonstrate how GaAs nanoscale membranes can be seamlessly integrated on silicon by controlling the density of nuclei in the initial stages of growth. We also correlate the absence or presence of defects with the existence of a single or multiple nucleation regime for the single membranes. Certain defects exhibit well-differentiated spectroscopic features that we identify with cathodoluminescence and micro-photoluminescence techniques. Overall, this work presents a new approach for the seamless integration of compound semiconductors on silicon.

The growth of compound semiconductors on silicon has been widely sought after for decades, but reliable methods for defect-free combination of these materials have remained elusive. Recently, interconnected GaAs nanoscale membranes have been used as templates for the scalable integration of nanowire networks on III-V substrates. Here, we demonstrate how GaAs nanoscale membranes can be seamlessly integrated on silicon by controlling the density of nuclei in the initial stages of growth. We also correlate the absence or presence of defects with the existence of a single or multiple nucleation regime for the single membranes. Certain defects exhibit well-differentiated spectroscopic features that we identify with cathodoluminescence and micro-photoluminescence techniques. Overall, this work presents a new approach for the seamless integration of compound semiconductors on silicon. ; LMSC acknowledges funding from Swiss National Science Foundation through the NCCR QSIT and project nr IZLRZ2_163861. H2020 program through project Indeed. VGD acknowledges Russian Science Foundation for financial support under grant 19-72-30004. IMN acknowledge funding from the Spanish MINECO (TEC2015-64189-C3-2-R, EUIN2017- 88844, RYC-2017-21995, BES-2013-065340), the Community of Madrid (P2018/EMT-4308), and the European Union FEDER, FSE. EURAMET EMPIR 17FUN06 SIQUST. AMR acknowledges the service from the X-SEM Laboratory at IMN, and funding from MINECO under project CSIC13-4E-1794 with support from EU (FEDER, FSE). SMS acknowledges funding from "Programa Internacional de Becas 'la Caixa'-Severo Ochoa". ICN2 acknowledge funding from Generalitat de Catalunya 2017 SGR 327. ICN2 is supported by the Severo Ochoa program from Spanish MINECO (grant no. SEV-2017-0706) and is funded by the CERCA Programme/Generalitat de Catalunya. Part of the present work has been performed in the framework of Universitat Autònoma de Barcelona Materials Science PhD program. Part of the HAADF-STEM microscopy was conducted in the Laboratorio de Microscopias Avanzadas at Instituto de Nanociencia de Aragon-Universidad de Zaragoza. This work has received funding from the European Union's Horizon 2020 Research and Innovation Programme under grant agreement no. 654360 NFFA-Europe. We acknowledge support from CSIC Research Platform on Quantum Technologies PTI-001. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no 823717 – ESTEEM3.

Topological qubits based on Majorana Fermions have the potential to revolutionize the emerging field of quantum computing by making information processing significantly more robust to decoherence. Nanowires are a promising medium for hosting these kinds of qubits, though branched nanowires are needed to perform qubit manipulations. Here we report a gold-free templated growth of III–V nanowires by molecular beam epitaxy using an approach that enables patternable and highly regular branched nanowire arrays on a far greater scale than what has been reported thus far. Our approach relies on the lattice-mismatched growth of InAs on top of defect-free GaAs nanomembranes yielding laterally oriented, low-defect InAs and InGaAs nanowires whose shapes are determined by surface and strain energy minimization. By controlling nanomembrane width and growth time, we demonstrate the formation of compositionally graded nanowires with cross-sections less than 50 nm. Scaling the nanowires below 20 nm leads to the formation of homogeneous InGaAs nanowires, which exhibit phase-coherent, quasi-1D quantum transport as shown by magnetoconductance measurements. These results are an important advance toward scalable topological quantum computing. ; Authors from EPFL and U. Basel acknowledge funding through the NCCR QSIT. Authors from EPFL further thank funding from SNF (project no. IZLRZ2-163861) and H2020 via the ITN project INDEED. Work at U. Basel was partially supported by the Swiss NSF, and the Swiss Nanoscience Institute SNI. S.M.S. acknowledges funding from "Programa Internacional de Becas "la Caixa″-Severo Ochoa". J.A. and S.M.S. acknowledge funding from Generalitat de Catalunya 2017 SGR 327 and the Spanish MINECO coordinated project ValPEC (ENE2017-85087-C3). ICN2 acknowledges support from the Severo Ochoa Programme (MINECO, grant no. SEV2013-0295) and is funded by the CERCA Programme/Generalitat de Catalunya. This work has received funding from the European Union's Horizon 2020 Research and Innovation Programme under grant agreement no. 654360 NFFA-Europe. V.G.D. thanks the Ministry of Education and Science of the Russian Federation for financial support under grant no. 14-613-21-0055 (project ID RFMEFI61316 × 0055). L.J.L. acknowledges support of NSF DMR-1611341. M.O.H. acknowledges support of the NSF GRFP. NUCAPT received support from the MRSEC program (NSF DMR-1720139) at the Materials Research Center, the SHyNE Resource (NSF ECCS-1542205), and the Initiative for Sustainability and Energy (ISEN) at Northwestern University. ; Peer reviewed