Scandium nitride (ScN) is an emerging rock salt III-nitride semiconductor and has attracted significant interest in recent years for its potential thermoelectric applications as a substrate for high-quality epitaxial GaN growth and as a semiconducting component for epitaxial singlecrystalline metal/semiconductor superlattices for thermionic energy conversion. Solid-solution alloys of ScN with traditional III-nitrides such as Al x Sc 1Àx N have demonstrated piezoelectric and ferroelectric properties and are actively researched for device applications. While most of these exciting developments in ScN research have employed films deposited using low-vacuum methods such as magnetron sputtering and physical and chemical vapor depositions for thermoelectric applications and Schottky barrier-based thermionic energy conversion, it is necessary and important to avoid impurities, tune the carrier concentrations, and achieve high-mobility in epitaxial films. Here, we report the high-mobility and high-thermoelectric power factor in epitaxial ScN thin films deposited on MgO substrates by plasma-assisted molecular beam epitaxy. Microstructural characterization shows epitaxial 002 oriented ScN film growth on MgO (001) substrates. Electrical measurements demonstrated a high room-temperature mobility of 127 cm 2 /V s and temperature-dependent mobility in the temperature range of 50-400 K that is dominated by dislocation and grain boundary scattering. High mobility in ScN films leads to large Seebeck coefficients (À175 lV/K at 950 K) and, along with a moderately high electrical conductivity, a large thermoelectric power factor (2.3 Â 10 À3 W/m-K 2 at 500 K) was achieved, which makes ScN a promising candidate for thermoelectric applications. The thermal conductivity of the films, however, was found to be a bit large, which resulted in a maximum figure-of-merit of 0.17 at 500 K.

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Coherent transmission of Cooper pairs through a non-superconducting medium is a key challenge for hybrid electronics with superconductors, normal metals and semiconductors. While superconductor-normal metal-superconductor (SNS) junctions have been known for quite sometime, including a low carrier density region or a two-dimensional electron gas (2DEG) in the path of superconducting electrons is relatively less explored. Indeed, this is due to the limited choice of materials that would make ohmic contacts to such systems, while simultaneously supporting a superconducting phase. In this paper we show a coherent transmission of supercurrent through a degenerate semiconductor over a length ≈2μm with a critical magnetic field B c ≈8T at 1.6K and T c ≈5K at zero magnetic field. This length scale is much larger than the typical thickness of a Josephson junction. Our system is a fragment of a GaN nanowall network that has been shown to support a high mobility 2DEG (μ n >10 4 cm 2 V −1 s −1 ). The current and voltage probes were superconducting tungsten-gallium composite electrodes and the measurements could be done in four-probe geometry. We demonstrate ballistic type carrier transport with a near ideal transparency of 1 and a critical current (I c ) large enough such that the Josephson coupling parameter . Some features in magneto-transport data suggest that there is possibly a small magnetic moment forming in the semiconductor fragment. In addition the combination of a T c typical of elemental metallic superconductors, but a critical field that appears to be higher than the Clogston-Chandrasekhar limit, may be indicative of the emergence of a triplet pairing mechanism in these structures.

Integrating silicon and III-nitride technologies for high-speed and large bandwidth communication demands optically interconnected active components that detect, process, and emit photons and electrons. It is imperative that multifunctional materials can enhance the performance and simplify fabrication of such devices. Spontaneously grown GaN in the nanowall network (NwN) architecture simultaneously displays unprecedented optical and electrical properties. A two-order increase in band-edge emission makes it suitable for high-brightness light-emitting diodes and laser applications. Decorating this NwN with silver nanoparticles further enhances emission through plasmonic interactions and renders it an excellent surface-enhanced Raman spectroscopy substrate for biomolecular detection. The observation of very high electron mobility (approximately 104 cm2/Vs) and large phase-coherence length (60 μm) is a consequence of two-dimensional (2D) electron gas formation applicable for high electron mobility transistors. Detecting ballistic transport in the nanowalls confirms proximity-induced superconductivity (<5 K and 8 T). Charge separation properties render it a device material for UV photodetectors, photoanodes for water splitting, and thermionic field emitters.

Due to ultrabright and stable blue light emission, GaN has emerged as one of the most famous semiconductors of the modern era, useful for light-emitting diodes, power electronics, and optoelectronic applications. Extending GaN’s optical resonance from visible to mid- and-far-infrared spectral ranges will enable novel applications in many emerging technologies. Here we show hexagonal honeycomb-shaped GaN nanowall networks and vertically standing nanorods exhibiting morphology-dependent Reststrahlen band and plasmon polaritons that could be harnessed for infrared nanophotonics. Surface-induced dipoles at the edges and asperities in molecular beam epitaxy-deposited nanostructures lead to phonon absorption inside the Reststrahlen band, altering its shape from rectangular to right-trapezoidal. Excitation of such surface polariton modes provides a novel pathway to achieve far-infrared optical resonance in GaN. Additionally, surface defects in nanostructures lead to high carrier concentrations, resulting in tunable mid-infrared plasmon polaritons with high-quality factors. Demonstration of morphology-controlled Reststrahlen band and plasmon polaritons make GaN nanostructures attractive for infrared nanophotonics.