Showing papers on "Field electron emission published in 1982"

Behavior of the Si/SiO2 interface observed by Fowler-Nordheim tunneling

Abstract: Thin‐oxide (40–50 A) metal oxide semiconductor (MOS) structures are shown to exhibit, prior to large levels of electron tunnel injection, the near‐ideal behavior predicted for a uniform trapezoidal barrier with thick‐oxide properties. The oscillatory field dependence due to electron‐wave interference at the Si/SiO2 interface indicates an abrupt, one‐monolayer barrier transition (∼2.5 A) consistent with earlier work. After tunnel injection of 1017 –5×1018 electrons/cm2, the barrier undergoes significant degradation leading to enhanced tunneling conductance, with reproducible behavior observed among different samples. This effect is consistent with the generation of positive states in the region of the oxide near the Si/SiO2 interface (<20 A), where the tunneling electrons emerge into the oxide conduction band. Densities of positive‐charge and interface‐state buildup are also observed from capacitance‐voltage (C‐V) measurements and are found to be consistent with the observed tunneling dependence on positiv...

Electron field emission from broad-area electrodes

Abstract: In this review, measurements are surveyed for both dc and microwave electric fields. These show significant emission at applied fields typically 100 times smaller than those expected theoretically or measured experimentally for ideal microtip cathodes. Recent work is reviewed which studies on a microscopic scale this emission and the localized sites which produce it. Rather than forming sharp field enhancing projections, these sites often appear flat and are frequently associated with grain boundaries or insulating inclusions. Following an examination of various techniques for changing the emission of a given cathode, several theoretical models are considered which may explain some aspects of the observed emission characteristics.

Observation of positively charged state generation near the Si/SiO2 interface during Fowler–Nordheim tunneling

Abstract: In previous work, we have established that thin oxide (40–50 A) MOS structures exhibit, prior to large levels of Fowler–Nordheim injection, the ideal tunneling behavior of a uniform trapezoidal barrier with thick oxide properties With increasing levels of electron injection towards the Si/SiO2 interface (up to 6×1018 e/cm2), a build‐up of excess current results This behavior is shown to be due to the generation of positive states in the SiO2 about 14 A from the Si/SiO2 interface, giving excellent agreement with our analysis of charge‐assisted tunneling The approach is seen to offer a sensitive probe of the oxide interfacial region, capable of locating and detecting as few as 1010 cm−2 positive states Comparisons are made among three oxidation processes, revealing wet oxides to be more susceptible than dry oxides to the state generation process The results are consistent with the mechanism of breaking strained Si–O–Si bonds near the interface, observed in x‐ray photoelectron spectroscopy experiments

Ultra-fast field emitter array vacuum integrated circuit switching device

Abstract: A field-emitter switching device wherein a positive pulse is applied to a te (which is held at a bias potential V1 just below turn-on). A collector is held at a potential higher than the gate in order to collect emitted electrons from a field emitter source. As the voltage is applied to the gate, electrons are emitted immediately from the source and travel to the most positive potential at the collector. Because of the field emitter geometry, such electron transport is extremely fast. The ultra-fast switching speed is attained because the electrons reach near-maximum velocity within a few field tip diameters of the source.

Field ionization of deep levels in semiconductors with applications to Hg1−xCdxTe p‐n junctions

Abstract: Deep level‐to‐band tunneling is investigated as a source of excess current in narrow band semiconductors with specific application to Hg1−xCdxTe. The theoretical modeling is carried out by analogy with the Oppenheimer approach to the field ionization of hydrogen and the resulting expression for the transmission matrix element is found to be an improved version of the one originally derived by Price and Sah. The tunneling rate characteristics are governed primarily by the exponential term which is calculated using ‘‘exact’’ E‐k dispersion relations combined with a parabolic barrier field. The preexponential term displays a marked insensitivity to both deep level energy and choice of impurity potential for near midgap states. Application of the theory to find the generation‐recombination rate for the process leads to the anticipated ‘‘bump’’ in the forward bias I‐V characteristics of pn junctions for a suitably chosen range of device parameters. The first direct experimental observation of just such a bump ...

Field emission cathodes using commercial carbon fibers

Abstract: Field emission cathodes have been constructed using commercial carbon fiber products. Using carbon yarn, emission starts at 5–15 kV and 10–30 kV/cm. Current densities up to 10 A/cm2 are obtainable over 100 cm2. Felt and cloth of carbon fiber emit at 50 kV/cm and up, and allow current densities of 10–1000 A/cm2 over 10–100 cm2.

The Thermo‐Field Emission of Electrons in Arc Discharges

Abstract: Starting from the conventional theory of thermo-field emission of electrons from metal surfaces, the range of validity and the errors of several approximate emission formulae are examined that are additive or harmonic combinations of the limiting thermionic (Richardson) and field emission (Fowler—Nordheim) equations. An optimization of such kinds of equations results in the simple dependence (for example) (iTF electron current density, T temperature, F field strength, k, A, B etc. are constants), or (dependent on only one variable Y = T + β′F β′ = const.). If the emission equations are applied to arc cathodes, both T and F must be expressed as functions of the ion current (Ii) and the ion current density (ji); a simple interpolating formula of the electron current density je adapted to numerical results in the case of Cu cathodes becomes (Ā, B, C: constants).

Fowler-Nordheim emission from non-planar surfaces

Abstract: A mathematically closed form expression for the electric field between arbitrarily shaped surfaces is derived utilizing the techniques of differential geometry. This solution is then applied to the problem of Fowler-Nordheim emission from non-planar surfaces. Knowledge of the field everywhere on the emitting surface allows calculation of the current emitted. A comparison of these calculated values, with measurements made on textured polysilicon emission test structures, is made. The agreement is within 10% across eight orders of magnitude in current. The topological features of the emitting surface predicted by the computations are in agreement with those observed in scanning electron micrographs (SEM's).

Electron Emission from Gold Island Films

Abstract: The electron energy distribution from Au island films shows field emission and hot-electron emission in two different regions of the applied voltage. The two processes can be determined by their relative energetic position compared with UV photoelectrons and their dependence on the voltage applied. There are field emission in the high-voltage region (Up > 8 V) following the Fowler-Nordheim equation and electron excitation at low voltages (Up < 8 V). Bei der Elektronenemission aus Goldinselschichten sind zwei Prozesse unterscheidbar. Die Unterscheidung gelingt durch Mikrobereichs-Energieanalyse. Der Vergleich mit der energetischen Lage von UV-Photoelektronen ergibt Feldemission entsprechend der Fowler-Nordheim-Gleichung bei hoheren Probenspannungen (Up > 8 V) und eine Anregungsemission bei kleineren Spannungen (Up < 8 V). Die Messungen werden in einem Photoemissions-Elektronenmikroskop durchgefuhrt.

On conditioning: Reduction of secondary‐ and rf‐field emission by electron, photon, or helium impact

Abstract: rf conditioning is a well known procedure by which the electron emission in rf cavities is reduced, thereby permitting the attainment of higher field strengths. The reduction of electron emission in rf conditioning is explained by electron, photon, or He impact, which causes hydrocarbon adsorption and dehydrogenation and polymerization of adsorbed hydrocarbons. These newly formed radiation‐resistant compounds show strong inelastic scattering for slow electrons, which greatly reduces the secondary emission and field emission out of excited states (rf‐field emission).

Analysis of cathode-spot behavior in high-pressure discharge lamps

Abstract: The operation of hot cathodes in high pressure discharge lamps has been investigated in a manner similar to that described by Ecker5). The formalism of Dyke and Dolan8) has been used to calculated emission of electrons from the cathode as a function of temperature and electric field. The electric field at the cathode surface is calculated from ion current and cathode fall, the largest contribution to that field being developed in the free-fall sheath less than one mean free path in thickness at the cathode surface. Two solutions to the coupled system of equations are found: a low-field, diffuse-mode solution in which electron emission is by the Shottky-amplified thermionic process, cathode fall increases with increasing current density, and the cathode spot tends to expand to fill the entire extent of the cathode tip; and a high field, hot-spot mode in which electrons are emitted as a result of the temperature-field mechanism. The lowest cathode fall in the latter mode occurs when the potential drop across the free fall sheath equals the cathode fall required by the cathode energy balance. The operating mode of the discharge in a given lamp depends on which of the two modes has the lowest cathode fall. Examples of each occur in various lamps and can be accounted for with reasonable values of material constants. It is shown that the hot-spot mode is favored over the diffuse mode by high pressures and low cathode work function. The latter surprising result is accounted for by the fact that field emission, varying as exp (-φ3/2), is even more favored by low work function than thermionic emission.

The development of a high-definition cathode-ray tube using a carbon-fibre field-emission electron source

Abstract: Details of a current-efficient field-emission electron gun suitable for use in a cathode-ray tube are given. Such a gun, using a carbon-fibre emitter, was subsequently used as the basis for developing a prototype CRT whose performance is shown to compare very favourable in most respects with the corresponding conventional device employing a thermionic cathode. However, intensity fluctuations in the display remain to be eliminated before it can be adopted as a practical device.

Optical and field effect studies of the Hg0.7Cd0.3 Te–anodic oxide interface

Abstract: This paper reports the effects of visible light and applied electric field on the properties of the HgCdTe–anodic oxide interface. The surfaces of anodized n‐type crystals are accumulated with a fixed positive charge in the oxide on the order of 5×1011 cm−2. However, illumination with photons of energy ?2.2 eV can neutralize and even invert these surfaces. The original surface charge is restored by placing the sample in the dark for periods of minutes at room temperature and weeks at 77 K. Based on our measurement of the oxide energy gap of 3.4 eV, the photo‐induced surface charging is attributed to internal photoemission of electrons from the HgCdTe valence band to the oxide conduction band. These photoemitted electrons fall into deep traps in the oxide and neutralize the fixed positive charge. When stored in the dark, these trapped electrons are thermally excited from the traps and recombined in the semiconductor. Charge exchange between the oxide traps and semiconductor can also be promoted by applying...

Influence of Semiconductor Dielectric Function Spatial Dispersion on Charge Electrostatic Energy near the Semiconductor/Vacuum Interface and Field Emission Current

Abstract: The electrostatic charge energy W near the semiconductor/vacuum interface is calculated for a variety of models describing the semiconductor static dielectric function e(k) dependent on a momentum transferred k. It is shown that the correct account of this dependence leads to the finiteness of the energy W and the image force electrostatic field – σW/σz, when z O, where z is the distance from the interface. The potential barrier shape for the field emission from semiconductors is found and the dependences of the tunnel current density j on the applied field F, the temperature T and the doping impurity concentration n0 are calculated. It is shown that the spatial dispersion effects of e(k) essentially affect the magnitude of j, but do not change the dependence j(F) which follows from the Fowler-Nordheim classical formula. [Russian Text Ignored.]

The effects of surface treatments on the Pt/n-GaAs Schottky interface

Abstract: The effects of both chemical and laser annealing surface treatment on the electroplated Pt/n-GaAs interface have been studied. Surface studies were carried out using scanning Auger Electron Spectroscopy (SAES) while interface analysis used SAES along with noble ion sputtering. When the Pt/n-GaAs interface is used as a mixer diode, the mixer noise temperature is critically dependent on the chemical nature of that interface, as expressed through the ideality factor, η, and series resistance, Rs. Surface and interface information was obtained in the form of Ga-to-As ratios, (Ga/As), in range of 0.35 to ∼2.5. Both chemical treatment and laser annealing showed that excess As at the interface leads to high η values indicating high mixer noise temperatures. Since high η values were accompanied by low barrier heights, φB, it was concluded that excess As at the interface lowers the barrier height and decreases the barrier width. This enhanced field emission, an emission mode not acceptable for low mixer noise temperatures. To confine the emission mechanism to thermionic emission requires stoichiometric or Ga rich interfaces and alkaline solutions of H2O2 with slow etch rates were found to be best suited for this purpose. Cw laser annealing proved to be a useful technique to control (Ga/As) on GaAs where high vapor pressure of As (uncapped anneal) and high diffusion coefficient of Ga through SiO2 (capped anneal) were exploited. However, cw annealing was not found to be suitable for mixer diode processing even when Ga rich interfaces are desired, due to sample exposure to oxygen.

Enhanced Electron Emission from Positive Dielectric/Negative Metal Configurations on Spacecraft

Abstract: Results are presented of an experimental study of UV-enhanced electron emission from solar cell samples on metal substrate. The dielectric cover glass is given a positive voltage with respect to the metal, either by use of an electron beam or with an applied bias voltage to the metal substrate, or by shining UV light (? .1 sun) on the sample. For certain samples tested, the current from the sample to the chamber walls exhibited what we refer to as "enhanced emission": The current was noisy (unsteady) with time, and the current was greater than that expected considering photoemission and secondary emission. Strong enhanced electron emission was observed for samples with fused silica cover glasses, while the effect was much reduced for samples with ceria-doped microsheet coverglasses. The critical difference in the two samples appears to be the resistivity of the coverglasses. The high resistivity of the fused silica (? ? 1017 ?-cm as compared to 1013 ?-cm for ceria doped microsheet) allows a large buildup of positive charge very close to the exposed negative metal (interconnects, soldering bar). This triggers field emission from the exposed metal. The noiseness of the current with time indicates the positive ions of the dielectric are contributing to the current which suggests an accelerated surface degradation. This emission effect appears below 1 kV.

Diode characteristics in laser-recrystallized and conventional polycrystalline silicon

Abstract: Diode characteristics of lateral p+pn+ structures fabricated in laser-recrystallized and non-irradiated poly-silicon have been investigated for p-doping levels ranging from 1016- 1019cm-3. Leakage currents in laser-recrystallized material were found to be about two orders of magnitude lower than in non-irradiated material for low doping levels. At high doping levels almost no leakage current reduction was observed. An analysis of the leakage currents in terms of emission from grain boundary traps was performed and the results suggest a different mixture of thermionic emission and thermal field emission for the materials at low doping levels.

Field stimulated exoelectron emission from borosilicate glass

Abstract: Exoelectrons, those electrons in energy levels of solids which are not fed by normal conduction mechanisms, have been detected at the surface of various materials1. Emission of exoelectrons may occur during mechanical stress2, chemical reaction3, or on heating4 or irradiation by photons of suitable energy5. Thermally stimulated exoelectron emission gives rise to so-called glow curves, in which the emitted current goes through a maximum as the temperature is increased. Robertson1 has suggested that an electric field may stimulate exoelectron emission in an analogous manner to thermal and photo emission. We describe here experiments which demonstrate the phenomenon of field stimulated exoelectron emission (FSEE), and discuss its relation to steady-state emission.

Field emission thermal desorption spectroscopy

Abstract: Thermal desorption spectra from single crystal planes of a field emitter are obtained with the technique described The specimen temperature is varied linearly and the field emission current from the face of interest is recorded vs temperature Heating current and temperature measurements are transmitted to and from the tip using digital techniques via fiberoptic links to assure the high isolation necessary A microcomputer is used to control the entire system, produce the linear temperature sweep, and acquire and treat the data The desorption of hydrogen from the (111) plane of field‐evaporated tungsten is presented as a test of the technique; a comparison between our spectra and the data reported in the literature shows a good correlation between the field emission and the classical thermal desorption spectroscopy A good facet selectivity is obtained as proved by a result concerning H2 on W (210)

Cathodic needle growth from Mo(CO)6 vapors at higher electric fields

Abstract: It is shown that metallic needle crystals grow on electron emitting areas of field emission cathodes working in Mo(CO)6 vapor. The growth is driven by ions impinging from a field emission arc plasma, and the products are classified into two categories depending on the thermal energy supplied externally to the substrate: 1) Mo particles are agglomerated in dendritic shapes at ∼ 300-1300 K, and 2) whisker-like crystals with an unknown structure are obtained at ∼ 1300-1500 K. The high-temperature needles are capped with Taylor cones during the growth, and it is shown that they are a metastable phase of Mo.

Antimony ion source

Abstract: PURPOSE:To extract Sb ion by using eutectic alloys of two or more elements such as Sb and Au or Zn, Pb, Cu as ion source keeping low steam pressure in molten state utilizing the difference in the intensity of field emission. CONSTITUTION:The weight of Au and Sb are determined to make a predetermined composition. Au wire 7 is wound around tungsten filament 6 to make a spiral basket and Sb8 wrapped by the Au wire is held by a ceramic 5. When current is applied to the filament 6 to heat up the Au wire 7 and the Sb wire 8, the alloy begins to form at a contact surface and finally the alloy of prefixed composition is obtained. When electric field is applied to the molten metal through outside electrodes 9, the field emission is obtained only at the Sb ion. Using this ion source, the Sb ion seed of large current can be extracted through a fine hole with a very little scattering of energy by the field emission. The Sb ion beam can be focused by a lens.

Field Emission and Secondary Electron Emission from Nb3Sn Surfaces

Abstract: High-energy electron storage rings require powerful acceleration systems in order to cope with the large energy loss by synchrotron radiation. Because of their lower surface resistance, superconducting accelerating cavities offer a substantial gain in terms of the total power consumption, which makes their use in future large electron storage rings very interesting. At present, cavities made from niobium are under study for this purpose.1–4