Junction investigation of graphene/silicon Schottky diodes

ABSTRACT: Here we present a facile technique for the large-scale production of few-layer graphene flakes. The as-sonicated, supernatant, and sediment of the graphene product were respectively sprayed onto different types of silicon wafers. It was found that all devices exhibited current rectification properties, and the supernatant graphene devices have the best performance. Schottky junctions formed between graphene flakes and silicon n-type substrates exhibit good photovoltaic conversion efficiency while graphene/p-Si devices have poor light harvesting capability.     

Leakage current analysis of diamond Schottky barrier diodes by defect imaging

The leakage current of pseudo-vertical-type diamond Schottky barrier diodes (SBDs) was analyzed using a defect visualization technique. Even under a low electrical field, 50% of the fabricated diamond SBDs exhibited a high leakage current that cannot be explained by any of the carrier transport mechanisms through the Schottky barrier. The SBDs with high leakage current were confirmed to contain a high density of dislocations that are revealed as deep etch pits by H₂/CO₂ plasma treatment. The maximum operation voltage of the SBDs is clearly dependent on the number of deep etch pits.     

Characterization of Schottky barrier diodes on a 0.5-inch single-crystalline CVD diamond wafer

In this study, Schottky barrier diodes were fabricated on a 0.5-inch single-crystalline diamond wafer, and the quality of the wafer as well as the performance of the devices were characterized. A rocking curve map indicated that the FWHM of the central 8 × 8-mm region was 10–50 arc sec, which is similar to that of high-quality HPHT single-crystalline diamond. The fabricated pVSBDs on the p^?/p⁺ stacked layer showed a high operation limit for the electrical field, with the mean value of this limit being higher than 2.5 MV/cm when the electrode was smaller than 300 µm. The performance of the devices seemed to be associated with the quality of the wafer. This indicates that the leakage current of a device is determined by the quality of the diamond wafer on which it is fabricated.     

Electrical characteristics of Al/polyindole Schottky barrier diodes. I. Temperature dependence

In this study, the forward and reverse bias current–voltage (I–V), capacitance–voltage (C–V), and conductance–voltage (G/ω–V) characteristics of Al/polyindole (Al/PIN) Schottky barrier diodes (SBDs) were studied over a wide temperature range of 140–400 K. Zero‐bias barrier height Φ_B0(I–V), ideality factor (n), ac electrical conductivity (σ_ac), and activation energy (E_a), determined by using thermionic emission (TE) theory, were shown fairly large temperature dispersion especially at lower temperatures due to surface states and series resistance of Al/PIN SBD. I–V characteristics of the Al/PIN SBDs showed an almost rectification behavior, but the reverse bias saturation current (I₀) and n were observed to be high. This high value of n has been attributed to the particular distribution of barrier heights due to barrier height inhomogeneities and interface states that present at the Al/PIN interface. The conductivity data obtained from G/ωV measurements over a wide temperature range were fitted to the Arrhenius and Mott equations and observed linear behaviors for σ_ac vs. 1/T and ln σ_ac vs. 1/T^1/4 graphs, respectively. The Mott parameters of T₀ and K₀ values were determined from the slope and intercept of the straight line as 3.8 × 10⁷ and 1.08 × 10⁷ Scm^?1K^1/2, respectively. Assuming a value of 6 × 10¹² s^?1 for ν₀, the decay length α^?1 and the density states at the Fermi energy level, N(E_F) are estimated to be 8.74 Å and 1.27 × 10²⁰ eV^?1cm^?3, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

High-current electron emission characteristics of cathodes based on diamond films

Using different gas source, four types of diamond thin films were prepared on silicon substrate by microwave plasma chemical vapor deposition (MPCVD) technology, and characterized in detail through scanning electron microscopy (SEM), Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. High-current pulsed emission characteristics, tested with a 2 MeV line-inducing injector, showed that all of CVD diamond films had high emission current density (> 70 A/cm²) and [100] textured B-doped microcrystalline diamond film possessed the largest emission current density of 115.1 A/cm². No obvious bright light and luminescent zones from side view CCD images indicated a possible pure field-emission mechanism of these diamond cathodes. Simultaneously, large decrease in the electron emission capability, above 15%, could be observed after several pulsed measurements, but this decrease could be completely recovered through the treatment of surface re-hydrogenation for emitted diamond cathodes, suggesting that emission performance of CVD diamond cathodes was closely relevant to hydrogen coverage ratio. The present data indicated that as-deposited CVD diamond films could be a potential candidate as cold cathode for the application in high-current electron emission field.     

Thermionic emission of amorphous diamond and field emission of carbon nanotubes

Thermal-field emission characteristics from nano-tips of amorphous diamond and carbon nanotubes at various temperatures are reported in this study. Amorphous diamond emitted more than 13 times more electrons at a temperature of 300 °C than at room temperature. In contrast, CNTs exhibited no increase of emitted current upon heating to 300 °C. The thermally agitated emission of amorphous diamond is attributed to the presence of defect bands. The formation of these defect bands raises the Fermi level into the upper part of the band gap, and thus reduces the energy barrier that the electrons must tunnel through. From defect bands within the band gap, the conduction band electrons were significantly increased due to electron tunnels from defect bands. The enhanced thermal-field emission originating from defect bands was observed in this study. This thermally agitated behavior of field emission for amorphous diamond was highly reproducible as observed in this research.     

Observation of electron field emission patterns from B-doped diamond films

To develop electron beam sources of carbon materials, field emission patterns were observed in three different setups. The first was a diode-type, in which a carbon specimen was facing to a positively biased fluorescence plate. The second was a triode-type, in which a positively biased grid was placed between them. In the third setup, a commercial electron gun was modified so that it could accommodate a carbon specimen and a grid. A fluorescence plate was placed in a vacuum chamber outside the gun. As the carbon specimen for electron emission source, B-doped diamond films, a single crystal diamond with a B-doped layer, an undoped diamond film and a glass-like carbon both with a fibrous structure at the surface, and a sponge carbon were used. It was found that electron emission from edges was dominant for 1×1 cm diamond films and carbon specimens in the diode-type setup. In the triode-type setup, the edges of the specimens were masked with a Kapton® tape. The electron emission occurred only from some spots on the specimen. In the electron gun setup, it was confirmed that an electron beam was generated, and a fairly uniform circle was seen on the fluorescence plate under defocused situation, while the circle became smaller by adjusting the current of the focusing lens. Although more uniform emission from the electron source materials seemed to be necessary for practical applications, it was demonstrated that an electron beam could be generated even in such a simple setup.     

Electrical and dielectric characteristics of Al/polyindole Schottky barrier diodes. II. Frequency dependence

The dielectric properties and ac electrical conductivity of Al/polyindole (Al/PIN) Schottky barrier diodes (SBDs) were investigated by using admittance spectroscopy (capacitance–voltage [C‐V] and conductance–voltage [G/ω‐V]) method. These C‐V and G/ω‐V characterizations were performed in the frequency range of 1 kHz to 10 MHz by applying a small ac signal of 40 mV amplitude from the external pulse generator, whereas the dc bias voltage was swept from (−10 V) to (+10 V) at room temperature. The values of dielectric constant (ε′), dielectric loss (ε″), dielectric loss tangent (tanδ), real and imaginary part of electrical modulus (M′ and M″), ac electrical conductivity (σ_ac), and series resistance (R_s) of the Al/PIN SBDs were found to be quite sensitive to frequency and applied bias voltage at relatively low frequencies. Although the values of the ε′, ε″, tanδ, and R_s of the device were observed to decrease with increasing frequencies, the electric modulus and σ_ac increased with increasing frequency for the high forward bias voltages. These results revealed that the interfacial polarization can more easily occur at low frequencies and that the majority of interface states (N_ss) between Al and PIN, consequently, contribute to deviation of dielectric properties of the Al/PIN SBDs. Furthermore, the voltage‐dependent profile of both R_s and N_ss were obtained from the C‐V and G/ω‐V characteristics of the Al/PIN SBDs at room temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

La3+、Cu2+、Fe3+/TiO2对金属-半导体表面肖特基势垒的影响

分析了金属-半导体表面的接触机理及肖特基势垒的形成，探讨了离子掺杂行为对势垒的影响机理，研究了光生载流子的迁移对TiO2半导体复合材料光催化活性的影响。结果表明,不同金属基体材料对表面势垒高度的影响程度不同，同掺杂离子的表面态对金属-半导体接触的影响也有差别,离子可以改变半导体功函数, La³⁺、Cu²⁺和Fe³⁺在同一浓度掺杂，对半导体的功函数影响不同，使载体和离子对电子和空穴捕获能力有所差异。     

电解槽系统泄漏电流的测算

运用电路分析原理，对电解槽的泄漏电流提出了测算方法以确定故障点。     

Field emission of polycrystalline diamond films grown by microwave-plasma chemical vapor deposition. I. Effects of surface morphology of diamond

The effects of surface morphology on the field emission of non-doped polycrystalline diamond films with thicknesses ranging from 5 to 55 μm were studied. Diamond films grown by a microwave-plasma chemical vapor deposition technique had both the diamond and non-diamond components with pyramidal and angular crystalline structures. Although the average crystallite size increased with increasing the film thickness (d), the volume fraction of the non-diamond components in the films was insensitive to the film thickness. However, the turn-on electric field, F_T, (defined as the low-end electric field to emit electrons) showed a U-shape dependence on the film thickness. This U-shape dependence was explained by a model in which the emission current was controlled by Fowler–Norheim tunneling of electrons at surface of the pyramids when d was thinner than 20 μm and by carrier transport in the polycrystalline diamond film when d was thicker than 20 μm. The lowest field of 4 V/μm was obtained in the film with 20 μm thick.     

Highly sensitive hydrogen sensor based on graphite-InP or graphite-GaN Schottky barrier with electrophoretically deposited Pd nanoparticles

Depositions on surfaces of semiconductor wafers of InP and GaN were performed from isooctane colloid solutions of palladium (Pd) nanoparticles (NPs) in AOT reverse micelles. Pd NPs in evaporated colloid and in layers deposited electrophoretically were monitored by SEM. Diodes were prepared by making Schottky contacts with colloidal graphite on semiconductor surfaces previously deposited with Pd NPs and ohmic contacts on blank surfaces. Forward and reverse current-voltage characteristics of the diodes showed high rectification ratio and high Schottky barrier heights, giving evidence of very small Fermi level pinning. A large increase of current was observed after exposing diodes to flow of gas blend hydrogen in nitrogen. Current change ratio about 700,000 with 0.1% hydrogen blend was achieved, which is more than two orders-of-magnitude improvement over the best result reported previously. Hydrogen detection limit of the diodes was estimated at 1 ppm H₂/N₂. The diodes, besides this extremely high sensitivity, have been temporally stable and of inexpensive production. Relatively more expensive GaN diodes have potential for functionality at high temperatures.     

Schottky diode architectures on p-type diamond for fast switching, high forward current density and high breakdown field rectifiers

The electrical properties of Schottky contacts on the (100) surface of Boron doped diamond films epitaxially grown on Ib substrates are investigated in this work. The role of Boron doping concentration and extended defects detected by cathodoluminescence is correlated to current voltage characteristics, rectifying efficiency and high voltage performance of the diodes up to 1 kV and more. The influence of surface treatment prior to metal deposition is highlighted and the choice of metal for the Schottky contact is discussed. The paramount importance of using an oxidised diamond surface at the Schottky contacts and outside is demonstrated. Decreasing the series resistance of diodes is obtained with a stack of two layers, the upper one being lightly doped while the deeper one contains Boron concentrations close to the metallic conductivity threshold (4 × 10²⁰ B/cm³). Several architectures are studied. The ohmic contact directly laid on the heavily doped layer permits forward current densities of 66 A/cm² under 4 V at room temperature and switching times in the nanosecond range. This set of results shows that p-type diamond is an adequate semiconductor for implementing high speed, high power and high voltage electronic rectifiers.     

Junction properties of Schottky diode based on composite organic semiconductors: Polyaniline-polystyrene system

Schottky barrier diode based on composite of polyaniline with polystyrene has been fabricated and characterized using aluminium as Schottky contact and platinum as an ohmic contact. The observed current-voltage characteristics can be satisfactorily fitted using the modified Schottky equation. Current-voltage (I-V) plots were non-linear and capacitance-voltage (C-V) plots were almost linear in reverse bias indicating rectification behavior. Various junction parameters were calculated from the temperature dependent I-V and C-V data and discussed. These results indicate that the composite materials have better mechanical strength and diode quality compared to the pure semiconducting polymer.     

Simplified model to predict the effect of the leakage current on primary and secondary current distributions in electrochemical reactors with a bipolar electrode

A simplified mathematical model to calculate the current distributions in bipolar electrochemical reactors is proposed. The current distributions are deduced from a combination of the voltage balance in the reactor with a voltage balance including the electrolyte inlet and outlet. Thus, equations to predict the effect of geometric and operational variables on the current distributions at the electrodes are reported. The parameters acting upon the current distributions were lumped into two dimensionless variables and their effects on the current distributions are discussed. The primary current distributions are obtained as a limiting case. Comparisons between calculated and experimental primary current distributions are reported.     

A Study of Moisture Effects on Ti/Porous Silicon/Silicon Schottky Barrier

Results of capacitance-voltage and current-voltage measurements performed on Ti/porous silicon (PS)/p-Si diode structures are presented. A 5–10 increase of conductivity and capacity has been observed at f < 10000 Hz in response to the moisture change from 0 to 50%. Model of Schottky contact on thin PS layer with the charge carriers inside of pores and PS/Si interface is applied to explain the frequency dependence of conductivity/capacity as well as moisture effect.     

Fabrication of Schottky diode based on Zn electrode and polyaniline doped with 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt

The electrical properties, including current-voltage (I-V) and capacitance-voltage (C-V) characteristics, of ITO/polyaniline/Al and ITO/polyaniline/Zn Schottky diodes have been investigated. Polyaniline (PANI) was prepared chemically and doped with 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt (AMPSNa). The maximum conductivity value for PANI-AMPSNa films was 1.8 × 10⁻² S/cm at 0.5 weight ratio of AMPSNa. The values of various junction parameters such as ideality factor, barrier height and charge carrier concentration were calculated based on the thermionic emission theory. Zn electrode showed better rectifying behavior with PANI-AMPSNa film than Al electrode. The obtained C-V characteristics showed that the charge carrier concentration is in the range of 10¹⁶/cm³.     

Investigation in the role of hydrogen on the properties of diamond films grown using Ar/H2/CH4 microwave plasma

The transition of diamond grain sizes from micron- to nano- and then to ultranano-size could be observed when hydrogen concentration is being decreased in the Ar/CH₄ plasma. When grown in H₂-rich plasma (H₂ = 99% or 50%), well faceted microcrystalline diamond (MCD) surface with grain sizes of less than 0.1 μm are observed. The surface structure of the diamond film changes to a cauliflower-like geometry with a grain size of around 20 nm for the films grown in 25% H₂-plasma. In the Ar/CH₄ plasma, ultrananocrystalline diamond (UNCD) films are produced with equi-axed geometry with a grain size of 5-10 nm. The H₂-content imposes a more striking effect on the granular structure of diamond films than the substrate temperature. The induction of the grain growth process, either by using H₂-rich plasma or a higher substrate temperature increases the turn-on field in the electron field emission process, which is ascribed to the reduction in the proportion of grain boundaries.     

Growth and high current field emission of carbon nanofiber films with electroplated Ni catalyst

We report high current-density field emission from carbon nanofiber (CNF) films synthesized using electroplated Ni catalysts on gold-buffer layers via hot-filament chemical vapor deposition. High-density thick CNFs which had a solid structure without hollow cores and many protrusions on the outside of CNF body were formed. The protrusions consisted of buckled small graphitic sheets, and some protrusions had very small tip radius to which we attribute good field emission from CNF films. The maximum emission current of 3.67 mA was measured from the area of 4.9 × 10^{− 3} cm², corresponding to the current density of 750 mA/cm², at the electric field of 12.5 V/μm. There was a distinctive hysteresis in emission–current curves measured while ramping up and down the bias-voltage. The deviations between up- and down-sweep emission currents, and the slope change in Fowler–Nordheim curves were most prominent in medium-voltage and -current regime. Moreover, the emission–current hysteresis showed dependence on the pressure during measurement and the voltage-sweep speed. We propose that adsorbate-enhanced field emission and adsorbate desorption during field-emission measurement were responsible for the observed emission behavior.     

创建氯碱化工生产“无泄漏、零排放”工厂模式的探索与实践

减少现场设备管路的跑冒滴漏现象,回收利用生产中产生的副产物及废气、废水、废渣,达到节能减排,减少污染,实现清洁文明、绿色环保生产,能够最终达到化工生产“无泄漏、零排放”。这样,每年可为企业节能降耗、节约大量生产成本、使企业效益最大化,极大增强企业抵抗市场风险的能力。