With the advance in the plasmonics and metamaterials research field, it became more and more important to fabricate, thin and smooth Au metal films in a reliable way. Here, by thin films we mean that their average is height below 10 nm and their average roughness is below 5% of the total thickness. In this article, we investigated the use of amino-and mercapto-silanes to increase the adhesion of Au on Si wafers thus obtaining a smooth and thin layer. This method do not include the uses of other metals to improve the adhesion of gold, like Ti or Cr, since they would reduce the optical characteristics of the structure. Our results show that layers having 6 nm thickness and below 0.3 nm roughness can be reproducibly obtained using amino-silanes. Layers having a nominal thickness of 5 nm have a yield of 50% thus this thickness is the limit for the process that we investigated.
Quantum dots tuned to atomic resonances represent an emerging field of hybrid quantum systems where the advantages of quantum dots and natural atoms can be combined. Embedding quantum dots in nanowires boosts these systems with a set of powerful possibilities, such as precise positioning of the emitters, excellent photon extraction efficiency and direct electrical contacting of quantum dots. Notably, nanowire structures can be grown on silicon substrates, allowing for a straightforward integration with silicon-based photonic devices. In this work we show controlled growth of nanowire-quantumdot structures on silicon, frequency tuned to atomic transitions. We grow GaAs quantum dots in AlGaAs nanowires with a nearly pure crystal structure and excellent optical properties. We precisely control the dimensions of quantum dots and their position inside nanowires and demonstrate that the emission wavelength can be engineered over the range of at least 30 nm around 765 nm. By applying an external magnetic field, we are able to fine-tune the emission frequency of our nanowire quantum dots to the D 2 transition of 87 Rb. We use the Rb transitions to precisely measure the actual spectral line width of the photons emitted from a nanowire quantum dot to be 9.4 ± 0.7 μeV, under nonresonant excitation. Our work brings highly desirable functionalities to quantum technologies, enabling, for instance, a realization of a quantum network, based on an arbitrary number of nanowire single-photon sources, all operating at the same frequency of an atomic transition.
Semiconducting nanowires, unlike bulk, can be grown in both wurtzite and zincblende crystal phases. this unique feature allows for growth and investigation of technologically important and previously unexplored materials, such as wurtzite AlGaAs. Here we grow a series of wurtzite AlGaAs nanowires with Al content varying from 0.1 to 0.6, on silicon substrates and through a comparative structural and optical analysis we experimentally derive, for the first time, the formula for the bandgap of wurtzite AlGaAs. Moreover, bright emission and short lifetime of our nanowires suggest that wurtzite AlGaAs is a direct bandgap material.Polytypism 1 is an exceptional property of nanowires and a new degree of freedom which enables the engineering of the electronic structure without change of material. For example, today's atomically-precise control over the crystal-phase switching in nanowires 2,3 allows to grow strain-free polytypic formations along the growth axis 4,5 , even small enough to form quantum dots 6,7 . The wurtzite phase is not observable at ambient conditions in bulk of any A III B V materials except for nitrides, while it can be obtained in nanowires. For this property and its technological implications, a great deal of attention has been drawn, in recent years, to nanowires system from scientific community 8-10 . However, for designing of novel structures and devices, knowledge of bandgaps and band alignments of the different crystal phases of new materials is crucial.In particular, Al X Ga 1-X As nanowires provide a promising platform for fabrication of advanced devices. For example, adding the Al component to the widely studied GaAs 11,12 allows to tune the emission in a wide range of wavelengths while, AlGaAs, having higher energy than GaAs, allows the combination of these two materials to fabricate strain-free quantum devices 13 .However, the knowledge about wurtzite AlGaAs is limited in the literature [14][15][16][17] , and is mainly grown as a shell around wurtzite GaAs core 15,16 . Importantly, the bandgap of wurtzite AlGaAs was neither predicted theoretically nor measured experimentally.In this work, we grow wurtzite AlGaAs nanowires, in a wide range of Al content x, and we present a comparative optical and structural study, empirically revealing the trend for the bandgap of wurtzite Al X Ga 1-X As. We grow our samples by Au-catalyzed vapor-liquid-solid technique in a molecular beam epitaxy (MBE) reactor (see methods section for details) obtaining high crystalline quality structures with any chosen Al content.
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The data on growth peculiarities and physical properties of GaAs insertions embedded in AlGaAs nanowires grown on different (1 1 1) substrates by Au-assisted molecular beam epitaxy are presented. The influence of nanowires growth conditions on structural and optical properties is studied in detail. It is shown that by varying the growth parameters it is possible to form structures like quantum dots that emit in a wide wavelengths range. These quantum dots show sharp and intense emission lines when an optical signal is collected from a single nanowire. The technology proposed opens new possibilities for integration of direct-band A III B V materials on silicon platform.
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