Venus long-life surface package (VL2SP)

Measurements in the atmosphere and at the surface of Venus are required to understand fundamental processes of how terrestrial planets evolve and how they work today. While the European Venus community is unified in its support of the EnVision orbiter proposal as the next step in European Venus exploration, many scientific questions also require in situ Venus exploration. We suggest a long-duration lander at Venus, which would be capable of undertaking a seismometry mission, operating in the 460°C surface conditions of Venus. Radar maps have shown Venus to be covered with volcanic and tectonic features, and mounting evidence, including observations from Venus Express, suggests that some of these volcanoes are active today. Assessing Venus' current seismicity, and measuring its interior structure, is essential if we are to establish the geological history of our twin planet, for example to establish whether it ever had a habitable phase with liquid water oceans. Although some constraints on seismic activity can be obtained from orbit, using radar or ionospheric observation, the most productive way to study planetary interiors is through seismometry. Seismometry requires a mission duration of months or (preferably) years. Previous landers have used passive cooling, relying on thermal insulation and the lander's thermal inertia to provide a brief window of time in which to conduct science operations - but this allows mission durations of hours, not months. Proposals relying on silicon electronics require an electronics enclosure cooled to < 200 °C; the insulation, cooling and power system requirements escalate rapidly to require a > 1 ton, > €1bn class mission, such as those studied in the context of NASA flagship missions. However, there are alternatives to silicon electronics: in particular, there have been promising advances in silicon carbide (SiC) electronics capable of operating at temperatures of 500°C. Within the coming decade it will be possible to assemble at least simple circuits using SiC components, sufficient to run a seismometry lander. We are proposing a Venus Long-Lived Surface Package (VL2SP) consisting of power source (RTG), science payload (seismometer and meteorology sensors), and ambient temperature electronics including a telecommunications system weighing < 100 kg. We do not specify how this VL2SP gets to the surface of Venus, but we estimate that an orbiter providing data relay would be essential. This presentation is based on a response sumitted to ESA's Call for New Scientific Ideas in September 2016

Reduction of the Schottky barrier height on silicon carbide using Au nano-particles

By the incorporation of size-selected Au nano-particles in Ti Schottky contacts on silicon carbide, we could observe considerably lower the barrier height of the contacts. This result could be obtained for both n- and p-type Schottky contacts using current-voltage and capacitance voltage measurements. For n-type Schottky contacts, we observed reductions of 0.19-0.25 eV on 4H-SiC and 0.15-0.17 eV on 6H-SiC as compared with particle-free Ti Schottky contacts. For p-type SiC, the reduction was a little lower with 0.02-0.05 eV on 4H- and 0.10-0.13 eV on 6H-SiC. The reduction of the Schottky barrier height is explained using a model with enhanced electric field at the interface due to the small size of the circular patch and the large difference of the barrier height between Ti and Au

Reduction of the barrier height and enhancement of tunneling current of titanium contacts using embedded Au nano-particles on 4H and 6H silicon carbide

We have investigated the electrical characteristics of Ti Schottky contacts with embedded Au nano-particles on various types of epilayers of SiC (4H- and 6H-SiC). From our current-voltage (I-V) and capacitance-voltage (C-V) measurements, we observed that Ti Schottky contacts with embedded Au nano-particles had 0.19 eV (n-4H-SiC) and 0.15 eV (n-6H-SiC) lower barrier height than those of particle free Ti Schottky contacts. In order to understand this reduction of the Schottky barrier height (SBH) for Ti Schottky contacts with embedded Au nano-particles, it has been proposed that SBH lowering is caused by an enhanced electric field due to the small size of the Au nano-particles and the large SBH difference. We have also tested these contacts on highly doped nand p-type SiC material to study ohmic contacts using linear TLM measurements

High-Temperature Electronic Materials: Silicon Carbide and Diamond

The physical and chemical properties of wide-band-gap semiconductors make these materials an ideal wide bandgapsemiconductor choice for device fabrication for applications in many different areas, e.g. light emitters, high-temperature and high-power electronics, high-power microwave devices, micro-electromechanical system (MEM) technology, and substrates for semiconductor preparation. These semiconductors have micro-electromechanical system (MEMS) been recognized for several decades as being suitable for these applications, but until recently the low material quality has not allowed the fabrication of high-quality devices. In this material quality chapter, we review the wide-band-gap semiconductors, silicon carbide and diamond. Silicon carbide electronics is advancing from the research stage to commercial production. The commercial availability of single-crystal SiC substrates during the early 1990s gave rise to intense activity in the development of silicon carbide devices. The commercialization started with the release of blue light-emitting diode (LED). The recent release of high-power Schottky diodes was a further demonstration of the progress made towards defect-free SiC substrates. Diamond has superior physical and chemical properties. Silicon-carbide- and diamond-based diamondsilicon carbide (SiC) electronics are at different stages of development. The preparation of high-quality single-crystal substrates of wafer size has allowed recent significant progress in the fabrication of several types of devices, and the development has reached many important milestones. However, high-temperature studies are still scarce, and diamond-based electronics is still in its infancy