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In this Letter, low-temperature (400 °C) chemical vapor deposition-grown boron nitride (BN) was investigated as the gate dielectric for AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MISHEMTs) on a Si substrate. Comprehensive characterizations using x-ray photoelectron spectroscopy, reflection electron energy loss spectroscopy, atomic force microscope, high-resolution transmission electron microscopy, and time-of-flight secondary ion mass spectrometry were conducted to analyze the deposited BN dielectric. Compared with conventional Schottky-gate HEMTs, the MISHEMTs exhibited significantly enhanced performance with 3 orders of magnitude lower reverse gate leakage current, a lower off-state current of 1 × 10−7 mA/mm, a higher on/off current ratio of 108, and lower on-resistance of 5.40 Ω mm. The frequency-dependent conductance measurement was performed to analyze the BN/HEMT interface, unveiling a low interface trap state density (Dit) on the order of 5 × 1011–6 × 1011 cm−2 eV−1. This work shows the effectiveness of low-temperature BN dielectrics and their potential for advancing GaN MISHEMTs toward high-performance power and RF electronics applications. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate the high performance of β-Ga2O3 metal–insulator–semiconductor (MIS) diodes. An ultrathin boron nitride (BN) interlayer is directly grown on the Ga2O3 substrate by pulsed laser deposition. X-ray photoelectron spectroscopy, Raman spectroscopy, and high-resolution transmission electron microscopy confirm the existence of a 2.8 nm BN interlayer. Remarkably, with the insertion of the ultrathin BN layer, the breakdown voltage is improved from 732 V for Ga2O3 Schottky barrier diodes to 1035 V for Ga2O3 MIS diodes owing to the passivated surface-related defects and reduced reverse leakage currents. Our approach shows a promising way to improve the breakdown performance of Ga2O3-based devices for next-generation high-power electronics. [ABSTRACT FROM AUTHOR]

van der Waals solids have been recognized as highly photosensitive materials that compete conventional Si and compound semiconductor based devices. While 2-dimensional nanosheets of single and multiple layers and 1-dimensional nanowires of molybdenum and tungsten chalcogenides have been studied, their nanostructured derivatives with complex morphologies are not explored yet. Here, we report on the electrical and photosensitive properties of WS2 nanowire-nanoflake hybrid materials we developed lately. We probe individual hybrid nanostructured particles along the structure using focused ion beam deposited Pt contacts. Further, we use conductive atomic force microscopy to analyze electrical behavior across the nanostructure in the transverse direction. The electrical measurements are complemented by in situ laser beam illumination to explore the photoresponse of the nanohybrids in the visible optical spectrum. Photodetectors with responsivity up to ∼0.4 AW−1 are demonstrated outperforming graphene as well as most of the other transition metal dichalcogenide based devices. [ABSTRACT FROM AUTHOR]

We have developed a continuously tunable, broadband terahertz attenuator with a transmission tuning range greater than 10³. Attenuation tuning is achieved electrically, by simply changing the DC voltage applied to a heating wire attached to a bulk silicon wafer, which controls its temperature between room temperature and ~550 K, with the corresponding free-carrier density adjusted between ~1011 cm-3 and ~ 1017cm-3 . This "hot-silicon"-based terahertz attenuator works most effectively at 450-550 K (corresponding to a DC voltage variation of only ~7 V) and completely shields terahertz radiation above 550 K in a frequency range of 0.1-2.5 THz. Both intrinsic and doped silicon wafers were tested and demonstrated to work well as a continuously tunable attenuator. All behaviors can be understood quantitatively via the free-carrier Drude model taking into account thermally activated intrinsic carriers. [ABSTRACT FROM AUTHOR]

We report on the electronic transport properties of single-layer thick chemical vapor deposition (CVD) grown molybdenum disulfide (MoS2) field-effect transistors (FETs) on Si/SiO2 substrates. MoS2 has been extensively investigated for the past two years as a potential semiconductor analogue to graphene. To date, MoS2 samples prepared via mechanical exfoliation have demonstrated field-effect mobility values which are significantly higher than that of CVD-grown MoS2. In this study, we will show that the intrinsic electronic performance of CVD-grown MoS2 is equal or superior to that of exfoliated material and has been possibly masked by a combination of interfacial contamination on the growth substrate and residual tensile strain resulting from the high-temperature growth process. We are able to quantify this strain in the as-grown material using pre- and post-transfer metrology and microscopy of the same crystals. Moreover, temperature-dependent electrical measurements made on as-grown and transferred MoS2 devices following an identical fabrication process demonstrate the improvement in field-effect mobility. [ABSTRACT FROM AUTHOR]

Optical absorption of thin-film single-walled carbon nanotubes was investigated. The excitation energies were tailored by controlling the film thickness and the average nanotube diameter. The lowest absorption band (S1, peaked at ∼0.68 eV) moves toward higher energy with increasing nanotube film thickness linearly at 5.5 meV/μm, due to the band-gap increase of stretched nanotubes stacked in the film. A subsequent heating of nanotube films at 400°C in air could further shift the S1 band upward for over 35 meV. We created a tandem structure by combining multiple nanotube layers with different diameter distributions in order to define a particular excitation energy. Our nanotube thin films are macrodevices with tunable optical properties in optoelectronic and photonic applications. [ABSTRACT FROM AUTHOR]

Y-branched Bi nanowires (NWs) embedded in anodic aluminum oxide templates were synthesized by electrochemical deposition. Transmission electron microscope observations revealed that the “stem” and the “branches” of the Y-branched Bi NWs are about 80 and 50 nm in diameter, respectively. Selected area electron diffraction studies showed that both the stem and the branches are single crystalline. Current–voltage measurement revealed that the parallel Y-branched Bi NWs have characteristics of conventional metal–semiconductor junctions. Our approach to produce one-dimensional metal–semiconductor junctions using Y-branched NWs consisting of only one kind of semimetal and without any external doping can be exploited to create metal–semiconductor junctions of other semimetals, which may find various applications in nanodevices. [ABSTRACT FROM AUTHOR]

We have studied the adsorption of H[sub 2]O molecules on a single-wall carbon nanotube (NT) using first-principles gradient-corrected density-functional theory. Subsequently, Green's function-based Landauer-Büttiker multichannel formalism within a tight-binding model is used to calculate the electron transport, and our results suggest that H[sub 2]O molecules adsorbed on the NT surface reduce the electronic conduction in the tube in agreement with recent experimental measurements. The decrease of conductance with water adsorption is explained on the basis of charge transfer between the adsorbate and the NT. [ABSTRACT FROM AUTHOR]