The van der Waals heterostructures of two-dimensional (2D) atomic crystals constitute a new paradigm in nanoscience. Hybrid devices of graphene with insulating 2D hexagonal boron nitride (h-BN) have emerged as promising nanoelectronic architectures through demonstrations of ultrahigh electron mobilities and charge-based tunnel transistors. Here, we expand the functional horizon of such 2D materials demonstrating the quantum tunneling of spin polarized electrons through atomic planes of CVD grown h-BN. We report excellent tunneling behavior of h-BN layers together with tunnel spin injection and transport in graphene using ferromagnet/h-BN contacts. Employing h-BN tunnel contacts, we observe enhancements in both spin signal amplitude and lifetime by an order of magnitude. We demonstrate spin transport and precession over micrometer-scale distances with spin lifetime up to 0.46 nanosecond. Our results and complementary magnetoresistance calculations illustrate that CVD h-BN tunnel barrier provides a reliable, reproducible and alternative approach to address the conductivity mismatch problem for spin injection into graphene.

We demonstrate that 3.5% in-plane lattice mismatch between GaN (0001) epitaxial layers and SiC (0001) substrates can be accommodated without triggering extended defects over large areas using a grain-boundary-free AlN nucleation layer (NL). Defect formation in the initial epitaxial growth phase is thus significantly alleviated, confirmed by various characterization techniques. As a result, a high-quality 0.2-lm thin GaN layer can be grown on the AlN NL and directly serve as a channel layer in power devices, like high electron mobility transistors (HEMTs). The channel electrons exhibit a state-of-the-art mobility of >2000 cm 2 /V-s, in the AlGaN/GaN heterostructures without a conventional thick C-or Fe-doped buffer layer. The highly scaled transistor processed on the heterostructure with a nearly perfect GaN-SiC interface shows excellent DC and microwave performances. A peak RF power density of 5.8 W/mm was obtained at V DSQ ¼ 40 V and a fundamental frequency of 30 GHz. Moreover, an unpassivated 0.2-lm GaN/AlN/SiC stack shows lateral and vertical breakdowns at 1.5 kV. Perfecting the GaN-SiC interface enables a GaN-SiC hybrid material that combines the high-electron-velocity thin GaN with the high-breakdown bulk SiC, which promises further advances in a wide spectrum of high-frequency and power electronics. Published by AIP Publishing.

We investigate the spin transport and precession in graphene by using the Hanle effect in nonlocal and threeterminal measurement geometries. Identical spin lifetimes, spin diffusion lengths and spin polarizations are observed in graphene devices for both techniques over a wide range of temperatures. The magnitude of the spin signals is well explained by spin transport models. These observations rules out any signal enhancements or additional scattering mechanisms at the interfaces for both geometries. This validates the applicability of both the measurement methods for graphene based spintronics devices and their reliable extractions of spin parameters.Keywords: Graphene, Hanle, Nonlocal, Three-Terminal, Spintronics, Spin transportThe spin degree of freedom of electrons is considered as an alternative state variable for processing information beyond the charge based CMOS technology. Its potential lies in the possibilities for a new generation of computers that can be non-volatile, faster, smaller, and capable of simultaneous data storage and processing with a reduced energy consumption 1. The strong interest in graphene and silicon based spintronic devices stems from their potentially long spin coherence lengths due to the absence of hyperfine interactions and a weak spin-orbit coupling. Such materials could be employed in the recently proposed concept of all spin logic using spins in ferromagnets to store information and communicate between them using a spin current 2 . All spin logic is particularly powerful since it combines various spin related phenomena such as spin injection, transport and detection with magnetization dynamics.In order to achieve these goals various methods for electrical spin injection and detection in metals 3, semiconductors [4][5][6] and graphene 7 have been investigated. Primarily nonlocal (NL) and three-terminal (3T) methods are used for an electrical detection of the spin polarization [6][7][8][9] . The non-local geometry separates the current and voltage path to provide information about pure spin transport parameters. However, nanofabrication by electron beam lithography is necessary in order to achieve submicrometer structures and channel lengths 7 . Although the NL method has been widely used for spin transport measurements in more conducting metals