Low Onset Voltage Research Articles

Low onset voltage of GaN on Si Schottky barrier diode using various recess depths

A low onset voltage AlGaN/GaN diode with a width of 14 mm is achieved. The recess depth of the AlGaN layer is responsible for the low onset voltage. In comparison with the conventional non-recessed diode, the onset voltage reduces by 45% along with a decrease of reverse leakage current by about one order of magnitude.

Negative differential resistance in graphene-nanoribbon–carbon-nanotube crossbars: a first-principles multiterminal quantum transport study

We simulate quantum transport between a graphene nanoribbon (GNR) and a single-walled carbon nanotube (CNT) where electrons traverse vacuum gap between them. The GNR covers CNT over a nanoscale region while their relative rotation is 90 degrees, thereby forming a four-terminal crossbar where the bias voltage is applied between CNT and GNR terminals. The CNT and GNR are chosen as either semiconducting (s) or metallic (m) based on whether their two-terminal conductance exhibits a gap as a function of the Fermi energy or not, respectively. We find nonlinear current-voltage (I-V) characteristics in all three investigated devices---mGNR-sCNT, sGNR-sCNT and mGNR-mCNT crossbars---which are asymmetric with respect to changing the bias voltage from positive to negative. Furthermore, the I-V characteristics of mGNR-sCNT crossbar exhibits negative differential resistance (NDR) with low onset voltage $V_\mathrm{NDR} \simeq 0.25$ V and peak-to-valley current ratio $\simeq 2.0$. The overlap region of the crossbars contains only $\simeq 460$ carbon and hydrogen atoms which paves the way for nanoelectronic devices ultrascaled well below the smallest horizontal length scale envisioned by the international technology roadmap for semiconductors. Our analysis is based on the nonequilibrium Green function formalism combined with density functional theory (NEGF-DFT), where we also provide an overview of recent extensions of NEGF-DFT framework (originally developed for two-terminal devices) to multiterminal devices.

Sulfur- and Nitrogen-Doped, Ferrocene-Derived Mesoporous Carbons with Efficient Electrochemical Reduction of Oxygen

Development of inexpensive and sustainable cathode catalysts that can efficiently catalyze the oxygen reduction reaction (ORR) is of significance in practical application of fuel cells. Herein we report the synthesis of sulfur and nitrogen dual-doped, ordered mesoporous carbon (SN-OMCs), which shows outstanding ORR electrocatalytic properties. The material was synthesized from a surface-templating process of ferrocene within the channel walls of SBA-15 mesoporous silica by carbonization, followed by in situ heteroatomic doping with sulfur- and nitrogen-containing vapors. After etching away the metal and silica template, the resulting material features distinctive bimodal mesoporous carbon frameworks with high nitrogen Brunauer-Emmett-Teller specific surface area (of up to ∼1100 m(2)/g) and uniform distribution of sulfur and nitrogen dopants. When employed as a noble-metal-free electrocatalyst for the ORR, such SN-OMC shows a remarkable electrocatalytic activity; improved durability and better resistance toward methanol crossover in oxygen reduction can be observed. More importantly, it performs a low onset voltage and an efficient nearly complete four-electron ORR process very similar to the observations in commercial 20 wt % Pt/C catalyst. In addition, we also found that the textural mesostructure of the catalyst has superseded the chemically bonded dopants to be the key factor in controlling the ORR performance.

High-performance 4H-SiC junction barrier Schottky diodes with double resistive termination extensions

4H-SiC junction barrier Schottky (JBS) diodes with a high-temperature annealed resistive termination extension (HARTE) are designed, fabricated and characterized in this work. The differential specific on-state resistance of the device is as low as 3.64 mΩ·cm2 with a total active area of 2.46 × 10−3 cm2. Ti is the Schottky contact metal with a Schottky barrier height of 1.08 V and a low onset voltage of 0.7 V. The ideality factor is calculated to be 1.06. Al implantation annealing is performed at 1250°C in Ar, while good reverse characteristics are achieved. The maximum breakdown voltage is 1000 V with a leakage current of 9 × 10−5 A on chip level. These experimental results show good consistence with the simulation results and demonstrate that high-performance 4H-SiC JBS diodes can be obtained based on the double HARTE structure.

Small onset voltages in negative corona discharges using the edges of gold and aluminum foils as nano-structured electrodes

Gold and aluminum foils with nano-structured edges were investigated as electrodes for corona discharges in nitrogen and ambient air. Low onset voltages were observed due to the field enhancement near the edges of the foil. The lowest onset voltage was determined to be about 1.2 kV in ambient air and about 1.1 kV in nitrogen for a 5 mm inter-electrode spacing. This is significantly smaller than the values reported in the literature for sharp tips with similar electrode spacing. The foil-based electrode tips are extremely simple to produce, making them candidates for low-cost, low power consumption and easily available corona-discharge technology.

Effect of TiO2 supporting layer on Fe2O3 photoanode for efficient water splitting

For an electrochemical water splitting system, titanate nanotubular particles with a thickness of ∼700nm produced by a hydrothermal process were repetitively coated on fluorine-doped tin oxide (FTO) glass via layer-by-layer self-assembly method. The obtained titanate/FTO films were dipped in aqueous Fe solution, followed by heat treatment for crystallization at 500°C for 10min in air. The UV–vis absorbance of the Fe-oxide/titanate/FTO film showed a red-shifted spectrum compared with the TiO2/FTO coated film; this red shift was achieved by the formation of thin hematite-Fe2O3 and anatase-TiO2 phases verified using X-ray diffraction and Raman results. The cyclic voltammetry results of the Fe2O3/TiO2/FTO films showed distinct reversible cycle characteristics with large oxidation–reduction peaks with low onset voltage of I–V characteristics under UV–vis light illumination. The prepared Fe2O3/TiO2/FTO film showed much higher photocurrent densities for more efficient water splitting under UV–vis light illumination than did the Fe2O3/FTO film. Its maximum photocurrent was almost 3.5 times higher than that obtained with Fe2O3/FTO film because of the easy electron collection in the current collector. The large current collection was due to the existence of a TiO2 base layer beneath the Fe2O3 layer.

Tungsten Oxide Buffer Layers Fabricated in an Inert Sol‐Gel Process at Room‐Temperature for Blue Organic Light‐Emitting Diodes

WO3 deposition from tungsten ethoxide precursor solutions at room temperature is demonstrated. The W(OEt)6 precursor can be converted under inert conditions and hence avoids sample contamination with oxygen, opening a pathway to more stable devices. The stoichiometry of all WO3 layers and the optoelectronic performance of the respective SMOLEDs well match thermally evaporated WO3 and its corresponding SMOLEDs. The solution processed WO3 hole injection layers enable the fabrication of blue phosphorescent OLEDs with low onset voltage and current efficiencies of up to 14 cd A(-1) .

Alternating pyrene–fluorene linear copolymers: Influence of non-conjugated and conjugated pyrene on thermal and optoelectronic properties

In order to explore the influence of non-conjugated and conjugated pyrene on the properties of polymers, four alternating pyrene–fluorene linear copolymers, PDOF-PPF, PDAOPF-PPF, PDOF-P and PDAOPF-P (Scheme 1), were designed, synthesized and characterized. They show greatly higher thermal stability than their oligomers due to curving of polymer chain. They also show high Tg due to high internal rotation barrier originated from large pyrene group. For non-conjugated pyrene substituted PDOF-PPF and PDAOPF-PPF, absorption spectra show sharp peak at about 354nm, which should be attributed to intramolecular interaction of pyrene and main conjugation. And in contrast, conjugated pyrene substituted PDOF-P and PDAOPF-P show structureless spectra. They also show stable spectra even annealed due to the high internal rotation barrier originated from pyrene. The spectra data are consistent with electrochemical and calculated data. It proves that conjugated pyrene plays much less contribution to frontier orbitals than non-conjugated pyrene. At last, the polymers were used as emitter to fabricated PLEDs, and the devices showed low onset voltage of about 4V, with maximum brightness of 1050 and 1520cd/m2 for PDOF-PPF and PDAOPF-PPF as emitters.

Fast GaN based Schottky diodes on Si(111) substrate with low onset voltage and strong reverse blocking

AbstractGaN‐based heterostructure lateral Schottky barrier diodes (SBD) grown on Si(111) substrate are presented in this work. These SBDs own very low onset‐voltage, VF = 0.50 V, high reverse blocking VBR > 600 V for LAC > 8 µm, very low capacitive charge of 0.415 nC/A and a very fast recovery time of 6 ps extracted under large signal operation conditions. These unique qualities are achieved by combining lateral topology, AlGaN back‐barrier epitaxial structure, fully recessed Schottky anode (ϕB = 0.62 eV) and anode field plate extension (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Low Driving Voltage and High Efficiency Blue Phosphorescent OLEDs with Mixed Host System

We report both low driving voltage and high efficiency characteristics in blue phosphorescent organic light-emitting diodes with a simple device structure. A mixed host system consisting of narrow band-gap host material of 4,4’,4’’-tris(N-carbazolyl)triphenylamine (TCTA) and bipolar carrier transporting material of 2,6-bis(3-(carbazol-9-yl)phenyl)pyridine (26DCzPPy) shows low driving voltage performances with high luminance stability. A very low onset voltage of 3.0 V and a driving voltage of 3.8 V to obtain a brightness of 1000 cd/m2are achieved with a current efficiency of 44.2 cd/A.

A new hematite photoanode doping strategy for solar water splitting: oxygen vacancy generation

The enhancement of the electrical conductivity by doping is important in hematite (α-Fe(2)O(3)) photoanodes for efficient solar water oxidation. However, in spite of many successful demonstrations using extrinsic dopants, such as Sn, Ti, and Si, the achieved photocurrent is still lower than the practical requirement. There is still lack of our understanding of how intrinsic oxygen defects can change the photocurrent and interact with the extrinsic dopants. In this study, we systematically investigate the interplay of oxygen vacancies and extrinsic Sn dopants in the context of photoanodic properties. As a result, we demonstrate that the controlled generation of oxygen vacancies can activate the photoactivity of pure hematite remarkably and further enhance the Sn doping effects synergistically. Furthermore, the correlated behavior of oxygen vacancies and Sn dopants is closely linked to the variation of electrical conductance and results in the optimum concentration region to show the high photocurrent and low onset voltage.

Extremely low driving voltage electrophosphorescent green organic light-emitting diodes based on a host material with small singlet–triplet exchange energy without p- or n-doping layer

In order to achieve low driving voltage, electrophosphorescent green organic light-emitting diodes (OLEDs) based on a host material with small energy gap between the lowest excited singlet state and the lowest excited triplet state (ΔEST) have been fabricated. 2-biphenyl-4,6-bis(12-phenylindolo[2,3-a] carbazole-11-yl)- 1,3,5-triazine (PIC–TRZ) with ΔEST of only 0.11eV has been found to be bipolar and used as the host for green OLEDs based on tris(2-phenylpyridinato) iridium(III) (Ir(ppy)3). A very low onset voltage of 2.19V is achieved in devices without p- or n-doping. Maximum current and power efficiencies are 68cd/A and 60lm/W, respectively, and no significant roll-off of current efficiency (58cd/A at 1000cd/m2 and 62cd/A at 10,000cd/m2) have been observed. The small roll-off is due to the improved charge balance and the wide charge recombination zone in the emissive layer.

Fast-Switching GaN-Based Lateral Power Schottky Barrier Diodes With Low Onset Voltage and Strong Reverse Blocking

GaN-based heterostructure lateral Schottky barrier diodes (SBDs) grown on n-SiC substrate are investigated in this letter. These SBDs own very low onset voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> = 0.43 V, high reverse blocking V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BR</sub> >; 1000 V, very low capacitive charge of 0.213 nC/A, and a very fast recovery time of 10 ps. These unique qualities are achieved by combining lateral topology, GaN:C back-barrier epitaxial structure, fully recessed Schottky anode (φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> = 0.43 eV), and slanted anode field plate in a robust and innovative process. Diode operation at elevated temperature up to 200 °C was also characterized.

Simple Structure and High Efficiency Phosphorescent OLEDs Using Narrow Band-gap Bipolar Host Material

ABSTRACTWe report high-efficiency phosphorescent blue OLEDs with an organic three stacked structure. Using a high-triplet-energy-hole transporting material of TAPC and a high-triplet-energy-electron transporting material of TmPyPB, the organic three stacked structure has been realized with three new narrow band-gap blue host materials. These host materials have bipolar characteristics and high triplet energy of &gt;2.8 eV. Very low onset voltages of 2.8~3.0 V and driving voltages of 4.2~4.6 V to obtain a brightness of 1000 cd/m2 are achieved in this three stacked device configuration. Maximum external quantum efficiency above 20% is reported.

Helium corona-assisted air discharge

Operation of atmospheric discharge of electronegative gases including air at low voltages yet without consuming any inert gas will enormously promote the application of non-thermal plasmas. By taking advantage of the low onset voltage for helium corona, air discharge was successfully launched at much reduced voltages with a needle-plate system partly contained in a helium-filled glass bulb—for a needle-plate distance of 12 mm, 1.0 kV suffices. Ultraviolet emission from helium corona facilitates the discharging of air, and the discharge current manifests distinct features such as relatively broad Trichel pulses in both half periods. This design allows safe and economic implementation of atmospheric discharge of electronegative gases, which will find a broad palette of applications in surface modification, plasma medicine and gas treatment, etc.

Efficient Metal-Free Oxygen Reduction in Alkaline Medium on High-Surface-Area Mesoporous Nitrogen-Doped Carbons Made from Ionic Liquids and Nucleobases

Mesoporous nitrogen-doped carbon materials with high surface areas up to 1500 m(2) g(-1) were conveniently made by the carbonization of nucleobases dissolved in an all-organic ionic liquid (1-ethyl-3-methylimidazolium dicyanamide). Using hard templating with silica nanoparticles, this process yields high-surface-area nitrogen-doped carbon materials with nitrogen contents as high as 12 wt %, narrow mesopore size distribution of ca. 12 nm diameter, and local graphitic carbon structure. It is demonstrated that the resulting nitrogen-doped carbons show very high catalytic activity, even in the metal-free case in the oxygen reduction reaction (ORR) for fuel cells. Specifically, the as-prepared materials exhibit a low onset voltage for ORR in alkaline medium and a high methanol tolerance, compared with those of commercial 20 wt % Pt/C catalyst. We regard this as a first step toward an all-sustainable fuel cell, avoiding noble metals.

Electroluminescent block copolymers containing oxadiazole and thiophene via ATRP

Block copolymers containing thiophene units in one block and oxadiazole (OXD) units in the other were prepared. Atom transfer radical polymerization method was used to obtain the thiophene-containing mesogen-jacketed polymers, and the kinetic study indicated that the polymerization was controllable and the polymers could be used to initiate the polymerization of the OXD-containing monomers. Photoluminescent spectra indicated that the fluorescence quantum yields of the polymers increased with increasing content of OXD. And, more OXD domains, that is, more interfaces between the hole-transport parts and electron-transport parts, resulting in the higher probability of exciplex formation. The electroluminescent devices containing the block copolymer with 64 mol % OXD as the emissive layer had a maximum brightness of 127 cd/m2 and an extremely low onset voltage of 7.7 V, which indicated that the injection and transport of charge carriers were facilitated and the number of charge carriers was sufficiently high in early time after the voltage was turned on. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Low-Voltage, Simple-Structure, High-Efficiency p–i–n-Type Electrophosphorescent Blue Organic Light-Emitting Diodes

We present simple p–i–n structures with single-emitting and mixed emitting layers for highly efficient phosphorescent blue organic devices. Using a high-triplet-energy-hole-transporting material of 1,1-bis(4-methylphenyl)-aminophenyl-cyclohexane (TAPC) and a high-triplet-energy-electron-transporting material of 1,3,5-tris(m-pyrid-3-ylphenyl)benzene (Tm3PyPB), the p–i–n structure has been realized by doping with MoO3 as a p-dopant and Cs2CO3 as an n-dopant. A very low onset voltage of 3.0 V and a driving voltage of 4.0 V to obtain a brightness of 1000 cd/m2 are achieved in this p–i–n device configuration. A maximum external quantum efficiency of 23.9% and a power efficiency of 36.7 lm/W are reported.

Red electrophosphorescent platinum(II) quinolinolate complexes

Luminescent organoplatinum complexes featuring 8-quinolinolates as chelating ligands have been synthesized and characterized. Substitution of the quinolinolate ligand has been achieved in the 5 position, where benzoyl substituents were introduced by reacting 8-hydroxyquinoline and the corresponding benzoyl chloride in a Friedel–Crafts acylation. The resulting complexes, κ2(N,C2)-(2-(4-tert-butylphenyl)pyridine)-κ2(N,O)-(5-(4-tert-butylphenyl)(8-quinolinolato-5-yl)methanone)platinum(II) and κ2(N,C2)-(3-hexyloxy-2-phenylpyridine)-κ2(N,O)-((8-quinolinolato-5-yl)phenylmethanone)platinum(II), have been investigated by nuclear magnetic resonance and infrared spectroscopy, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, X-ray analysis, thermal analysis, cyclic voltammetry, UV–vis absorption spectroscopy, and luminescence measurements in solution and in the solid state. The solid-state structures of the complexes were found to be dominated by π–π intermolecular interactions. Organic light-emitting devices based on the complexes and a matching host material gave red to near-infrared electroluminescence with low-onset voltages (4–5 V) and continuous wave luminance intensities exceeding 500 cd/m2.

High power efficiency in Si-nc/SiO2 multilayer light emitting devices by bipolar direct tunneling

We demonstrate experimentally bipolar (electrons and holes) current injection into silicon nanocrystals in thin nanocrystalline-Si/SiO2 multilayers. These light emitting devices have power efficiency of 0.17% and turn-on voltage of 1.7 V. The high electroluminescence efficiency and low onset voltages are attributed to the radiative recombination of excitons formed by both electron and hole injection into silicon nanocrystals via the direct tunneling mechanism. To confirm the bipolar character, different devices were grown, with and without a thick silicon oxide barrier at the multilayer contact electrodes. A transition from bipolar tunneling to unipolar Fowler–Nordheim tunneling is thus observed.