Controlled generation of a pn-junction in a waveguide integrated graphene photodetector

With its electrically tunable light absorption and ultrafast photoresponse, graphene is a promising candidate for high-speed chip-integrated photonics. The generation mechanisms of photosignals in graphene photodetectors have been studied extensively in the past years. However, the knowledge about efficient light conversion at graphene pn-junctions has not yet been translated into high-performance devices. Here, we present a graphene photodetector integrated on a silicon slot-waveguide, acting as a dual-gate to create a pn-junction in the optical absorption region of the device. While at zero bias the photo-thermoelectric effect is the dominant conversion process, an additional photoconductive contribution is identified in a biased configuration. Extrinsic responsivities of 35 mA/W, or 3.5 V/W, at zero bias and 76 mA/W at 300 mV bias voltage are achieved. The device exhibits a 3 dB-bandwidth of 65 GHz, which is the highest value reported for a graphene-based photodetector.Comment: 19 pages, 16 figure

Large-signal model of the Metal-Insulator-Graphene diode targeting RF applications

We present a circuit-design compatible large-signal compact model of metal-insulator-graphene (MIG) diodes for describing its dynamic response for the first time. The model essentially consists of a voltage-dependent diode intrinsic capacitance coupled with a static voltage-dependent current source, the latter accounts for the vertical electron transport from/towards graphene, which has been modeled by means of the Dirac-thermionic electron transport theory through the insulator barrier. Importantly, the image force effect has been found to play a key role in determining the barrier height, so it has been incorporated into the model accordingly. The resulting model has been implemented in Verilog A to be used in existing circuit simulators and benchmarked against an experimental 6-nm TiO2 barrier MIG diode working as a power detector.Comment: 4 pages, 5 figures, 1 tabl

Towards a Critical Open-Source Software Database

Open-source software (OSS) plays a vital role in the modern software ecosystem. However, the maintenance and sustainability of OSS projects can be challenging. In this paper, we present the CrOSSD project, which aims to build a database of OSS projects and measure their current project "health" status. In the project, we will use both quantitative and qualitative metrics to evaluate the health of OSS projects. The quantitative metrics will be gathered through automated crawling of meta information such as the number of contributors, commits and lines of code. Qualitative metrics will be gathered for selected "critical" projects through manual analysis and automated tools, including aspects such as sustainability, funding, community engagement and adherence to security policies. The results of the analysis will be presented on a user-friendly web platform, which will allow users to view the health of individual OSS projects as well as the overall health of the OSS ecosystem. With this approach, the CrOSSD project provides a comprehensive and up-to-date view of the health of OSS projects, making it easier for developers, maintainers and other stakeholders to understand the health of OSS projects and make informed decisions about their use and maintenance.Comment: 4 pages, 1 figur

Nanosecond spin lifetimes in bottom-up fabricated bilayer graphene spin-valves with atomic layer deposited Al2_2O3_3 spin injection and detection barriers

We present spin transport studies on bi- and trilayer graphene non-local spin-valves which have been fabricated by a bottom-up fabrication method. By this technique, spin injection electrodes are first deposited onto Si$^{++}$/SiO$_2$ substrates with subsequent mechanical transfer of a graphene/hBN heterostructure. We showed previously that this technique allows for nanosecond spin lifetimes at room temperature combined with carrier mobilities which exceed 20,000 cm$^2$/(Vs). Despite strongly enhanced spin and charge transport properties, the MgO injection barriers in these devices exhibit conducting pinholes which still limit the measured spin lifetimes. We demonstrate that these pinholes can be partially diminished by an oxygen treatment of a trilayer graphene device which is seen by a strong increase of the contact resistance area products of the Co/MgO electrodes. At the same time, the spin lifetime increases from 1 ns to 2 ns. We believe that the pinholes partially result from the directional growth in molecular beam epitaxy. For a second set of devices, we therefore used atomic layer deposition of Al$_2$O$_3$ which offers the possibility to isotropically deposit more homogeneous barriers. While the contacts of the as-fabricated bilayer graphene devices are non-conductive, we can partially break the oxide barriers by voltage pulses. Thereafter, the devices also exhibit nanosecond spin lifetimes.Comment: 6 pages, 4 figure

Identifying suitable substrates for high-quality graphene-based heterostructures

We report on a scanning confocal Raman spectroscopy study investigating the strain-uniformity and the overall strain and doping of high-quality chemical vapour deposited (CVD) graphene-based heterostuctures on a large number of different substrate materials, including hexagonal boron nitride (hBN), transition metal dichalcogenides, silicon, different oxides and nitrides, as well as polymers. By applying a hBN-assisted, contamination free, dry transfer process for CVD graphene, high-quality heterostructures with low doping densities and low strain variations are assembled. The Raman spectra of these pristine heterostructures are sensitive to substrate-induced doping and strain variations and are thus used to probe the suitability of the substrate material for potential high-quality graphene devices. We find that the flatness of the substrate material is a key figure for gaining, or preserving high-quality graphene.Comment: 6 pages, 5 figure

A Survey of Dataspace Connector Implementations

The concept of dataspaces aims to facilitate secure and sovereign data exchange among multiple stakeholders. Technical implementations known as "connectors" support the definition of usage control policies and the verifiable enforcement of such policies. This paper provides an overview of existing literature and reviews current open-source dataspace connector implementations that are compliant with the International Data Spaces (IDS) standard. To assess maturity and readiness, we review four implementations with regard to their architecture, underlying data model and usage control language.Comment: 12 pages, 5 figure