Graphene as Transparent Electrode for Direct Observation of Hole Photoemission from Silicon to Oxide

The outstanding electrical and optical properties of graphene make it an excellent alternative as a transparent electrode. Here we demonstrate the application of graphene as collector material in internal photoemission (IPE) spectroscopy; enabling the direct observation of both electron and hole injections at a Si/Al2O3 interface and successfully overcoming the long-standing difficulty of detecting holes injected from a semiconductor emitter in IPE measurements. The observed electron and hole barrier heights are 3.5 eV and 4.1 eV, respectively. Thus the bandgap of Al2O3 can be further deduced to be 6.5 eV, in close agreement with the valued obtained by vacuum ultraviolet spectroscopic ellipsometry analysis. The detailed optical modeling of a graphene/Al2O3/Si stack reveals that by using graphene in IPE measurements the carrier injection from the emitter is significantly enhanced and the contribution of carrier injection from the collector electrode is minimal. The method can be readily extended to various IPE test structures for a complete band alignment analysis and interface characterization.Comment: 15 pages, 5 figure

High breakdown voltage AlGaN-GaNHEMTs achieved by multiple field plates

High-voltage Al0.22Ga0.78N-GaN high-electron mobility transistors have been fabricated using multiple field plates over dielectric passivation layers. The device breakdown voltage was found to increase with the addition of the field plates. with two field plates, the device showed, a breakdown voltage as high as 900 V. This technique is easy to apply, based on the standard planar transistor fabrication, and especially attractive for the power switching applications

Very high voltage operation (> 330 V) with high current gain of AlGaN/GaN HBTs

N-p-n Al0.05GaN/GaN heterojunction bipolar transistors with a common emitter operation voltage higher than 330 V have been demonstrated using selectively regrown emitters. Devices were grown by metalorganic chemical vapor deposition on sapphire substrates. The n-type emitter was grown selectively on a 100-nm-thick p-base with an 8 mum n-collector structure using a dielectric mask. The shallow etch down to the collector mitigates damages induced in the dry etch, resulting a low leakage and a high breakdown. The graded AlGaN emitter results in a common emitter current gain of similar to18 at an average collector current density of up to 1 kA/cm(2) at room temperature

Self-assembly and properties of domain walls in BiFeO3 layers grown via molecular-beam epitaxy

Bismuth ferrite layers, ∼200-nm-thick, are deposited on SrRuO 3 -coated DyScO 3 (110) o substrates in a step-flow growth regime via adsorption-controlled molecular-beam epitaxy. Structural characterization shows the films to be phase pure with substrate-limited mosaicity (0.012 ○x-ray diffraction ω-rocking curve widths). The film surfaces are atomically smooth (0.2 nm root-mean-square height fluctuations) and consistof 260-nm-wide [11̄1] o -oriented terraces and unit-cell-tall (0.4 nm) step edges. The combination of electrostatic and symmetry boundaryconditions promotes two monoclinically distorted BiFeO 3 ferroelectric variants, which self-assemble into a pattern with unprecedentedlycoherent periodicity, consisting of 145 ± 2-nm-wide stripe domains separated by [001] o -oriented 71 ○ domain walls. The walls exhibit electricalrectification and enhanced conductivity

Room temperature weak ferromagnetism in Sn1−xMnxSe2 2D films grown by molecular beam epitaxy

We discuss growth and magnetic properties of high-quality two dimensional (2D) Sn1−xMnxSe2 films. Thin films of this 2D ternary alloy with a wide range of Mn concentrations were successfully grown by molecular beam epitaxy. Mn concentrations up to x ≈ 0.60 were achieved without destroying the crystal structure of the parent SnSe2 2D system. Most important, the specimens show clear weak ferromagnetic behavior above room temperature, which should be of interest for 2D spintronic applications