The project WISEPHY will investigate physical-layer security schemes for wireless communications, a new emerging paradigm for secure communications that builds its theoretical foundations on information- theoretic principles. The general aim is to demonstrate through theoretical models, code design and proof-of- principle experiments that there is much to be gained by coding for security at the physical layer of wireless links. In fact, the security mechanisms of most wireless communications protocols are implemented in the upper layers of the communications architecture, assuming that the physical-layer has already been estab- lished. In contrast, several information-theoretic results suggest that the randomness inherently present in a wireless communication medium (fading, thermal noise, interference) can be harnessed to conceal infor- mation from potential eavesdroppers by coding at the physical-layer itself. This approach has been dubbed “physical-layer security” and has attracted considerable interest lately in the information theory community. Unfortunately, the promises of information theory have not yet translated into practical engineering solutions. Although the fundamental limits of secure communications over noisy channels are now better understood, few practical coding schemes exist that guarantee any level of physical-layer security. The project WISEPHY aims at bridging the gap between information theory and engineering solutions by addressing several relevant aspects of physical-layer security. The originality of the project stems from a comprehensive “bottom-up” approach, which explores information theoretic, coding theoretic, experimental and cryptographic facets of the problem. In particular, two key aspects of the project that break new ground are the design, analysis and implementation of practical coding schemes, as well as the cryptanalysis of these coding schemes in realistic settings.

While silicon-based solar cell technologies dominate the photovoltaic (PV) market today, their performance is limited. Indeed, the world record efficiency for Si-based PVs has been static at 25% for several years now. III-V multijunction PVs, on the other hand, have recently attained efficiencies > 40% and new record performances emerge regularly. Although tandem PV geometries have been developed combining crystalline and amorphous silicon, it has not been possible so far to form devices with efficiencies to rival III-V multijunctions. NOVAGAINS aims to benefit from combining the maturity of the Si technology with the potential efficiency gains associated with IIIV PV through the development of a novel tandem PV involving the integration of an InGaN based junction on a monocrystalline Si junction by means of a compliant ZnO interfacial template layer which doubles as a tunnel junction. Although the (In)GaN alloy has been used extensively in LEDs, its’ use in solar cell technology has drawn relatively little attention. Nevertheless, the InGaN materials system offers a huge potential to develop superior efficiency PV devices. The primary advantage of InGaN is the direct-band gap, which can be tuned to cover a range from 0.7 eV to 3.4 eV. As such, this is the only system which encompasses as much of the solar spectrum. Indeed, the fact that InGaN can provide such tunability of the bandgap means that PV conversion efficiencies greater than 50% can be anticipated. Unfortunately, it is very difficult to grow GaN based films of high materials quality directly on Si because they do not have a good crystallographic match. ZnO can be grown more readily on such substrates, however, because of its’ more compliant nature. Indeed, well-crystallized and highly-oriented ZnO can even be grown directly on the native amorphous SiO2 layer. Since ZnO shares the same wurtzite structure as GaN and there is less than 2% lattice mismatch it has been demonstrated that it is then possible to grow InGaN/GaN epitaxially on ZnO/Si using the specialized know-how offered by the consortium. Modeling indicates that when optimized, stacked InGaN and Si cells coupled by tunneling through a ZnO interlayer offer the perspective of tandem cells with overall solar conversion efficiencies in excess of 30%.

This proposal addresses the two major roadblocks in the development of graphene for high-performance nano-optoelectronics, namely how to efficiently and reliably integrate them in pristine conditions in electronic devices, and how harness the exceptional properties of graphene. Specifically, proof of principle of ultra-thin body tunnel field effect transistors (UB-TFET) are proposed consisting of two-dimensional (2D) all epitaxial graphene/boron nitride heterostructures with a viable large scale integration scheme. Tunnel transistors are an efficient alternative to standard field effect transistors designs that are inefficient for graphene because of the lack of a bandgap. Importantly UB-TFET should overcome the thermal limitation of thermioic sub-threshold swing in common transistors. The TFET will be based on epitaxial graphene on SiC (epigraphene, or EG)/BN structures; the most advanced implementation will utilize the recently discovered exceptional conductance properties of epigraphene nano-ribbons that are quantized single channel ballistic conductors at room temperature. But having excellent graphene is far from having a device and the active component has to be integrated. This project is based on the fundamental realization that only (hetero)-epitaxial growth can provide the required atomic control for reliable devices. Epitaxial growth insures clean interfaces and precise orientation of the stacked layers, avoiding trapped molecules and the randomness inherent to layer transfer. However, despite this absolute requirement, very little progress has been made up to now to grow large 2D dielectric on graphene; most dielectric deposition needs chemical modification of the graphene surface for adhesion, which invariably compromises the graphene electronic performance. Hexagonal boron nitride (h-BN) layers is considered the best substrate for graphene, but only micron size BN flakes are available, making the integration tedious, unreliable and impossible at large scale. In this proposal we will grow h-BN epitaxialy on epigraphene by metalorganic vapor phase epitaxy (MOVPE). As demonstrated in preliminary work by this three-team partnership, this technique provides exceptional unmatched graphene/h-BN epitaxial interfaces as required for high performance electronics, and immediate upscaling capabilities. The SiC/EG/h-BN heterostructure will give access to graphene properties in an exceptionally reproducible and clean environment, not otherwise available. Growth conditions will be investigated to produce ultra thin h-BN on epigraphene, which have not been achieved yet. This proposal will then follow two tracks to build UB-TFETs, demonstrating proof of principle of vertical and lateral BN/EG-based FETs. Our ultimate goal is to combine ballistic epigraphene nanoribbons in tunneling devices to enable a new generation of electronic devices. This is an extremely promising alternative to the standard FET paradigm that can enable ultra-high frequency operation as well as low power operation. This project is a tight well-focused partnership between three teams with a history of highly successful collaboration and perfect complementarity: CNRS-Institut Néel (Grenoble), CNRS/ONERA-Laboratoire d’Etude des Matériaux (Châtillon), and CNRS/Georgia Institute of Technology -UMI 2958 (Metz, in collaboration with GT Atlanta). We will build up on the important milestone of epitaxial h-BN growth on EG, towards critical development including ultra-thin BN and fabrication of tunnel transistors devices. IN will be in charge of providing epigraphene, will design and realized transistor devices and perform transport measurements; the UMI team will produce the BN epitaxial film and provide basic structural study for rapid optimization of the growth process; LEM will perform advanced structural and optical studies, in particular HR-TEM studies, critical to the layer characterization of ultra thin 2D films.