Effect Of Metal Contact Research Articles

Investigation on the effect of metal contacts on the vertical MnO2 nanowire array-based Schottky barrier diodes

Investigation on the effect of metal contacts on the vertical MnO2 nanowire array-based Schottky barrier diodes

CMOS-Compatible Photonic Phase Shifters With Extremely Low Thermal Crosstalk Performance

We report a thorough analysis of the thermal crosstalk issue for silicon photonic circuits using metal and doped silicon heaters for the two waveguide configurations, rib and strip waveguides. Full-wave thermal and optical simulations are performed and it is observed that integrated doped heaters with strip waveguides have the best thermal crosstalk performance. Also, the effect of metal contacts on the heater power consumption is investigated. Furthermore, to alleviate the phase crosstalk and improve the phase tuning efficiency, a deep trench is implemented to thermally shield an adjacent waveguide. Two well-known photonic components, namely, integrated Mach-Zehnder modulators and PN phase shifters are designed and the thermal crosstalk performance is analyzed rigorously. The proposed photonic phase shifter is outperformed in terms of thermal crosstalk over the existing designs. Such phase shifters are viable for compact silicon photonic circuits operating at a very high temperature.

The effects of metallic contacts on the lasing characteristics of organic thin films

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed

Ultrasensitive Heterojunctions of Graphene and 2D Perovskites Reveal Spontaneous Iodide Loss

Summary Despite the demonstrated high efficiency of perovskite solar cells and light-emitting devices, the understanding of the intrinsic stability of perovskites is far from complete. In this work, using an ultrasensitive, exfoliated 2D perovskite single-crystal sheet/graphene heterostructure device, we reveal spontaneous iodide loss as an important degradation pathway of 2D perovskite single crystals, which n-dopes the perovskite semiconductor by generating positively charged iodide vacancies. Furthermore, we show that covering perovskites with graphene can suppress the iodide loss, significantly improving perovskite stability. A perovskite phototransistor is demonstrated with a graphene/2D perovskite/graphene structure, which shows no degradation after 75 days. Our work not only provides important insights for future stable perovskite optoelectronic device development, but also demonstrates the potential of graphene as a promising sensitive diagnostic tool for device and material degradation studies.

Chemically enhanced double-gate bilayer graphene field-effect transistor with neutral channel for logic applications

In this article, we present the simulation, fabrication, and characterization of a novel bilayer graphene field-effect transistor exhibiting electron mobility up to ∼1600 cm2 V−1 s−1, a room temperature Ion/Ioff ≈ 60, and the lowest total charge (∼1011 cm−2) reported to date. This is achieved by combined electrostatic and chemical doping of bilayer graphene, which enables one to switch off the device at zero top-gate voltage. Using density functional theory and atomistic simulations, we obtain physical insight into the impact of chemical and electrostatic doping on bandgap opening of bilayer graphene and the effect of metal contacts on the operation of the device. Our results represent a step forward in the use of bilayer graphene for high-performance logic devices in the beyond-complementary metal−oxide−semiconductor (CMOS) technology paradigm.

The effect of metal-contacts on carbon nanotube for high frequency interconnects and devices

High frequency characterisation of platinum and tungsten contacts on individual multi-walled carbon nanotubes (MWNT) is performed from 10 MHz to 50 GHz. By measuring the scattering parameters of aligned individual MWNTs, we show that metal contacts enhance an inductive response due to the improved MWNT-electrode coupling reducing the capacitive effect. This behaviour is pronounced in the frequency below 10 GHz and strong for tungsten contacts. We explain the inductive response as a result of the interaction of stimulus current with the localized (or defects) states present at the contact region resulting in the current lagging behind the voltage. The results are further supported by direct current measurements that show tungsten to significantly increase carbon nanotube-electrode coupling. The immediate consequence is the reduction of the contact resistance, implying a reduction of electron tunnelling barrier from the electrode to the carbon nanotube.

DESIGN DEPENDENT CUTOFF FREQUENCY OF NANOTRANSISTORS NEAR THE ULTIMATE PERFORMANCE LIMIT

We have studied the effect of different structural designs of double gate MOSFETs (DG–MOSFETs) and carbon nanotube field effect transistors (CNTFETs) on the cutoff frequency (fT). The effects of metallic contacts with Schottky barriers, gate work function, dual material gate (DMG), halo doped channel and lightly doped drain and source (LDDS) architectures on the fT have been investigated for DG–MOSFETs and CNTFETs and the design dependent fT for both types of transistors has been studied for the first time. The simulations are based on the Schrödinger–Poisson solvers developed for each nanotransistor separately. The ballistic limit has been studied as the ultimate performance limit of the DG–MOSFETs and CNTFETs. The results of this paper, for the first time, show how some designations used for modification of short channel effects or current–voltage characteristics affect the fT. The results revealed that the cutoff frequencies of both types of the transistors exhibit the same behavior with changing design parameters. We have shown that the Schottky barriers, parasitic capacitances and halo doping reduce the fT and have proposed the DMG and LDDS artchitectures as ways to increase the fT for DG–MOSFETs and CNTFETs for the first time.

Controllable modification of the conduction properties of carbon nanotube devices through deposition of a metal overlayer onto the sidewalls

The effects of metal contacts and metal overlayers on the electrical properties of carbon nanotubes (CNTs) were studied. We show that the conduction properties of a CNT device can be controllably designed through metal depositions on the sidewall even though the conduction type is not clearly defined by the work function of the contact metal. The conversion from an n-type to a p-type conductor was observed with deposition of an overlayer using a large work function metal (Pd), whereas a p-type to n-type conversion was observed with deposition of an overlayer using a low work function metal (Ti). This behavior was attributed to charge transfer doping or the local bending of nanotube bands beneath the metal overlayer. First-principle calculations revealed that charge transfer doping may be uniquely defined by the work function difference if a metal layer forms a weak contact with the sidewall of a CNT.

Effects of metal contacts and dopants on the performance of ZnO-based memristive devices

We have performed a detailed investigation of the fabrication and switching characteristics of ZnO-based memristive devices. The effects of doping and various metal contacts have been studied. It is observed that, with the use of Al metal contacts and ZnO:Al layers, relatively high ROFF/RON ratios of 200 can be achieved. Much improved device stability and reproducibility, on the other hand, can be realized by using either nominally undoped or Mg-doped ZnO memristive layers. The experimental results may be well explained by an oxygen vacancy formation and migration model. The present work represents an important step in realizing high performance ZnO-based memristive devices for future nonvolatile memory applications.

Effects of Metallic Contacts on Electron Transport through Graphene

We report on a first-principles study of the conductance through graphene suspended between Al contacts as a function of junction length, width, and orientation. The charge transfer at the leads and into the freestanding section gives rise to an electron-hole asymmetry in the conductance and in sufficiently long junctions induces two conductance minima at the energies of the Dirac points for suspended and clamped regions, respectively. We obtain the potential profile along a junction caused by doping and provide parameters for effective model calculations of the junction conductance with weakly interacting metallic leads.

Effect of metal contacts on the electrical characteristics of Al2O3 dielectric thin films

The effect of top metal electrodes on the electrical characteristics of Al2O3 metal-insulator-metal capacitors is studied. The leakage current and breakdown characteristics were observed to have a strong dependence on the electrode material. Devices with Al electrodes exhibited significantly higher breakdown voltages compared to devices with Au, Ni, Cu, and Ag electrodes. Introducing an Al diffusion barrier dramatically increased the breakdown field and reduced the leakage current for capacitors with Ag, Au, and Cu electrodes. The electrical characteristics were found to relate well to material properties of the contacting metals, such as ionization potential and diffusion coefficient.

Dielectric Charging in Low Temperature Silicon Nitride for RF-MEMS Capacitive Switches

ABSTRACTThe paper presents a systematic investigation of dielectric charging in low temperature silicon nitride for RF-MEMS capacitive switches. The investigation takes includes both the effect of dielectric film thickness as well as the effect of metal contacts. The investigation demonstrates that the charging process is asymmetric. It is shown that the amount of stored charge depends significantly on the dielectric film thickness, which is caused from the contribution of the space charge polarization mechanism. Finally, the results are compared with those of higher temperature silicon nitride.

High performance ZnO nanowire field effect transistors with organic gate nanodielectrics:effects of metal contacts and ozone treatment

High performance ZnO nanowire field effect transistors (NW-FETs) were fabricated using ananoscopic self-assembled organic gate insulator and characterized in terms of conventionaldevice performance metrics. To optimize device performance and understand the effects ofinterface properties, devices were fabricated with both Al and Au/Ti source/drain contacts,and device electrical properties were characterized following annealing and ozonetreatment. Ozone-treated single ZnO NW-FETs with Al contacts exhibited an on-current(Ion) of∼4 µA at0.9 Vgs and1.0 Vds, a thresholdvoltage (Vth) of 0.2 V, asubthreshold slope (S) of ∼130 mV/decade, an on–offcurrent ratio (Ion:Ioff)of ∼107, and a fieldeffect mobility (μeff) of ∼1175 cm2 V−1 s−1.In addition, ozone-treated ZnO NW-FETs consistently retained the enhanced device performance metricsafter SiO2 passivation. A 2D device simulation was performed to explain the enhanced deviceperformance in terms of changes in interfacial trap and fixed charge densities.

Metal contacts in thin-film transistors

The effects of metal contacts on the electrical characteristics in thin-film transistors are discussed. It is found that the effects of these contacts are twofold. First, a constant potential that can range from zero to some volts (half the bandgap) is added to the entire channel. Second, a residual barrier is formed with a height that depends on the bias, and is in the order of tens of meV when a current is present. It is shown that these predicted effects are in agreement with experimental observations.

Silicon nanograins with aluminum contacts studied by the Density Functional method

The purpose of this study is the evaluation of the effects of metallic contacts on nanocrystalline silicon grains and is based on the use of the Density Functional theory. The structures considered are plated crystalline grains and the contacts are constructed by depositing an aluminum layer on the two opposite sides of the nanograin. The calculations indicate that, as for monolayer films deposited on bulk samples, the aluminum coating has a layered structure without clustering and with minimum intermixing with the silicon atoms. The built-in potential across the entire device has a functional dependence on the geometry of the nanograin and of the contacts. Potentially, this property is important for the fabrication of novel Schottky-barrier devices. However the strength of bonding is generally lower in the structures with contacts and this casts doubts on their stability.

Effects of metallic contacts on silicon nanostructures studied quantum mechanically

The purpose of this study is to get insight into the effects of metallic contacts on nanocrystalline silicon material. Therefore, the Hartree–Fock formulation at semi-empirical level has been applied to the characterization of realistic structures of silicon grains coated with an aluminum film. The calculations describe the electronic configuration of the grains and the effects exerted on it by the metallic atoms. The parameters investigated are the binding and adsorption energies, the ionization potential and the valence charges. Energy considerations favor structures with Al deposited atop of the silicon atoms without interdiffusion or lateral diffusion. The electronic properties of grains appear perceptibly altered by the metallic overlayer and the strength of bonding is generally lowered in the structures with the contacts. Furthermore, the built-in potential across the entire device exhibits a functional dependence on both the grain and the contact geometry which could be usefully applied for the fabrication of unconventional Schottky barriers devices.

Effect of metal contact's reflection on the effective coupling coefficient of second‐order DFB laser diodes

AbstractFor a second‐order DFB‐LD, the presence of a metal contact layer can reduce 1st‐order radiation. Part of the reflected power is redistributed into guided modes and results in a variation of the effective coupling coefficient κeff. In this paper, we study the effect of the Au top contact's reflection on the κeff of 2nd‐order DFB lasers. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 339–342, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20296

Effects of metallic contacts on silicon nanostructures studied quantum mechanically

The purpose of this study is to get insight into the effects of metallic contacts on nanocrystalline silicon material. Therefore, the Hartree–Fock formulation at semi-empirical level has been applied to the characterization of realistic structures of silicon grains coated with an aluminum film. The calculations describe the electronic configuration of the grains and the effects exerted on it by the metallic atoms. The parameters investigated are the binding and adsorption energies, the ionization potential and the valence charges. Energy considerations favor structures with Al deposited atop of the silicon atoms without interdiffusion or lateral diffusion. The electronic properties of grains appear perceptibly altered by the metallic overlayer and the strength of bonding is generally lowered in the structures with the contacts. Furthermore, the built-in potential across the entire device exhibits a functional dependence on both the grain and the contact geometry which could be usefully applied for the fabrication of unconventional Schottky barriers devices.

THE EFFECTS OF METALLIC CONTACTS ON SILICON NANOSTRUCTURES STUDIED QUANTUM MECHANICALLY

The purpose of this study is to get insight into the effects of metallic contacts on nanocrystalline silicon material. Therefore the Hartree–Fock formulation at semiempirical level has been applied to silicon grains coated with an aluminum film. The calculations describe the electronic configuration of the grains and the effects induced by the presence of the metallic atoms. The parameters investigated are the binding and adsorption energies, the ionization potential and the Mulliken charges. Though no inter-diffusion or lateral diffusion of metal atoms on silicon is observed, the electronic properties of grains appear perceptibly altered by the metallic overlayer and the strength of bonding is generally lowered in the structures with the contacts. Furthermore the built-in potential across the entire device exhibits a functional dependence on both the grain and the contact geometry which could be usefully applied for the fabrication of unconventional Schottky barriers devices.

Effects of contact metals on electroluminescence from embedded nanosize-Si-particle films.

Sandwich structures composed of metal and Si external layers with an intermediate embedded nanosize-Si-particle insulator layer have been fabricated. The insulator layer is composed of extra thin (\ensuremath{\sim}80 \AA{}) Si-rich silicon dioxide (ETSSO) films or extra thin (\ensuremath{\sim}80 \AA{}) silicon oxynitride (ETSON) films. Semitransparent Au, Pd, Ag, and Al films were used as contact metals. The effects of metal contacts on electroluminescence (EL) from the structures under forward biases are reported. For structures with either ETSSO and ETSON insulator layers, the EL peak positions appear at a distinctly longer wavelength when the contact metal has a large work function, such as Au or Pd, when compared with structures where the contact metal has a lower work function, such as Ag or Al. For a single contact metal, the EL peak position is almost independent of forward biases. The experimental results are difficult to be explained with a model of band to band radiative recombination of electron-hole pairs in nanosize Si particles, but can be better explained by a model in which electrons and holes tunnel into the insulator layer and radiatively recombine at the luminescence centers there. The metal work functions affect which types of luminescence centers determine the EL.