Transparent conductive Ga-doped ZnO (ZnO:Ga) was fabricated to serve as p-contacts of InGaN-based light-emitting diodes (LEDs) using molecular-beam epitaxy. As-grown ZnO:Ga films typically have resistivities of ¼ 2 À 4 Â 10 À4 Ácm, and over 80% transparency in the near UV and visible wavelength ranges. The current-voltage characteristics between as-grown ZnO:Ga contacts and p-GaN layers were ohmic. The brightness of LEDs fabricated with ZnO:Ga p-contacts was nearly double compared to LEDs with conventional Ni/Au p-contacts. We obtained the external efficiency as high as 20.8% in the case of the near UV LED. The forward voltage at 20 mA was found not to increase even after the lamp LED with ZnO:Ga were kept for 80 h in high humidity and high temperature environments.

We have studied the circular photogalvanic effect (CPGE) in Cu/Bi bilayers. When a circularly polarized light in the visible range is irradiated to the bilayer from an oblique incidence, we find a photocurrent that depends on the helicity of light. Such photocurrent appears in a direction perpendicular to the light plane of incidence but is absent in the parallel configuration. The helicity dependent photocurrent is significantly reduced for a Bi single layer film and the effect is nearly absent for a Cu single layer film. Conventional interpretation of the CPGE suggests the existence of spin-momentum locked band(s) of a Rashba type in the Cu/Bi bilayer. In contrast to previous reports on the CPGE studied in other systems, however, the light energy used here to excite the carriers is much larger than the band gap of Bi. Moreover, the CPGE of the Cu/Bi bilayer is larger when the energy of the light is larger: the helicity dependent photocurrent excited with a blue light is nearly two times larger than that of a red light. We therefore consider the CPGE of the Cu/Bi bilayer may have a different origin compared to conventional systems.Spin-momentum locked bands are one of the key signatures of the emergence of topologically protected states in topological insulators and Weyl semimetals [1]. Such bands also appear in heterostructures with broken structure inversion symmetry and/or large spin orbit coupling (SOC) [2][3][4]. The spin texture of the spin-momentum locked bands in the reciprocal space depends on the symmetry of the system. For example, the electron's spin and momentum directions are orthogonal to each other for systems that can be described by a Rashba Hamiltonian [5,6].The presence of spin-momentum locked bands within the bulk or at surfaces/interfaces allows generation of non-equilibrium spin accumulation when current is passed to the system [7,8]. Significant effort has been placed to generate spin accumulation in semiconductor heterostructures [9,10]. Recent studies have extended such effort into metallic heterostructures [2,6,11,12], where the SOC can be larger than that of typical semiconductor heterostructure constituents. Current-induced spin accumulation at interfaces has been reported in metallic heterostructures which manifests itself in magnetization switching and domain wall motion [13,14]. It is thus of high importance to identify the presence of spinmomentum locked bands in thin film heterostructures.Angle resolved photoemission spectroscopy (ARPES) is a powerful tool to study band structures and has been used to reveal the surface electronic states of, for example, topological insulators and Weyl semimetals[1]. However, its use is typically limited to clean surfaces and involves difficulty in studying interface states of films which are not particularly clean (e.g. films deposited by sputtering). To study spin-momentum locking of such interface states, it has been shown recently that combination of spin pumping and the inverse Rashba-Edelstein effect (IREE) allows its direct probing [2][3]...

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Recessed-gate GaN metal-oxide-semiconductor field-effect transistors with a double-insulator gate configuration demonstrate 10-MHz switching operation of which delay time is < 35 ns. The recess structure is fabricated by etching the Al 0.19 Ga 0.81 N layers to expose their underlying AlN layers. The devices include a thermally oxidized AlN layer onto which an Al 2 O 3 film is formed by atomic layer deposition, which works as a gate insulator. This structure performs enhancement-mode operation with a typical threshold voltage of 1.4 V. A maximum drain current of 158.3 mA/mm is achieved at 6 V gate bias and maximum transconductance is 52.1 mS/mm at 10 V drain bias. Index Terms-10-MHz switching operation, Al 2 O 3 , atomic layer deposition (ALD), double-insulator gate, enhancementmode (E-mode).

Biodiesel fuels (BDF) have many problems in the cold due to their crystallization properties. In particular, precipitation of large crystals of high-melting fractions in BDF at low temperatures remarkably changes cold flow property of BDF and, thereby, it increases the values of cold filter plugging point. In this study, we evaluated polyglycerol esters of fatty acids (PGE) and ethylene-vinyl acetate co-polymer (EVA) as chemical additives to improve the cold flow property of palm oil-based FAME (PFME). The results of solid fat content measurement indicate that the simultaneous addition of PGE and EVA showed synergistic effects on suppression of crystallization of PFME, however such effect was not observed when EVA was used alone. DSC thermograms indicated that the PGE additives not only decreased the crystallization temperature but also kinetically suppressed the crystal growth. Polarized light microscopy showed that the simultaneous addition of PGE and EVA led to the formation of considerably small and fine-dispersed crystals of PFME. These results indicate that combined effects of PGE and EVA caused the formation of finedispersed PFME crystals, which could improve the viscous properties of palm oil-based BDF at relatively cold temperatures.