Showing papers on "Field electron emission published in 1984"

Solar cell contact resistance—A review

Abstract: An overview of ohmic contacts on solar cells is presented The fundamentals of metal-semiconductor contacts are reviewed, including the Schottky approach, Fermi level pinning by surface states, and the mechanisms of thermionic emission, thermionic/field emission, and tunneling for current transport The concept of contact resistance is developed and contact resistance data for several different contact materials on both silicon and gallium arsenide over a range of doping densities are summarized Finally, the requirements imposed by solar cells on contact resistance are detailed

Resonant Fowler–Nordheim tunneling in n−GaAs‐undoped AlxGa1−xAs‐n+GaAs capacitors

Abstract: Periodic structure is observed in the current‐voltage characteristics at 4.2 K of n−GaAs‐AlxGa1−xAs‐n+GaAs capacitors, grown by molecular beam epitaxy, which have AlxGa1−xAs thicknesses of 30–35 nm. The periodicities can be explained quantitatively by the theory of resonant Fowler–Nordheim tunneling.

Switching and other nonlinear phenomena associated with prebreakdown electron emission currents

Abstract: An anode probe-hole technique, in conjunction with an electron spectrometer, has been used to study the short-term temporal changes in the emission characteristics of microscopically localised field emission sites on broad-area high voltage electrodes. The observed effects, e.g. the threshold switch-on of sites, and emission mode switching, have been discussed in terms of a new field-induced hot-electron emission model which is based on the concept of dielectric switching through the formation of microscopic conducting channels.

Thermionic‐field emission from interface states at grain boundaries in silicon

Abstract: An extension of Shockley–Read–Hall kinetics is presented for interface states at grain boundaries in silicon. The emission of majority carriers by these states is generalized to include thermionic field emission (TFE), which is shown to be important in many practical cases. Comparison is made with experimental results obtained on studies of isolated grain boundaries in silicon. One of the principal results is that energy distributions of interface states deduced from electrical characteristics of grain boundaries must be interpreted using a model which includes TFE. The importance of TFE increases with the doping concentration of the silicon N and the voltage applied across the grain boundary V and decreases with temperature. It is legitimate to neglect TFE from the interface states and consider pure thermal emission only for NV≲1016 cm−3 V at a temperature of 300 K, or NV≲1015 cm−3 V for 130 K.

Real and apparent effects of strong electric fields on the electron emission from midgap levels EL2 and EL0 in GaAs

Abstract: The effects of strong electric fields, up to 4×105 V/cm, on the electron emission from the GaAs dominant midgap levels EL2 and EL0 were investigated by employing differential capacitance transients on GaAs‐Au Schottky diodes. It was found that, in diodes with normal reverse bias characteristics, both levels exhibited a small field enhancement of electron emission, well within the range of the Poole–Frenkel effect. In contrast, very pronounced ‘‘apparent’’ electric field effects were observed in diodes with large reverse bias current. Thus, the conflicting reported results on the magnitude of the field enhancement of the electron emission from EL2 must be attributed to the characteristics of the Schottky diodes employed rather than to those of EL2.

Applications of Electron Holography Using a Field-Emission Electron Microscope

Abstract: L'holographie d'electrons permet le discernement de la phase de l'electron. Parmi plusieurs applications de l'holographie d'electrons, la microscopie interferentielle est prometteuse, les franges de contour du front d'onde d'electrons transmis indiquant les contours d'epaisseur d'un echantillon homogene et les lignes magnetiques de force d'un echantillon ferromagnetique

z1-oscillations in ion-induced kinetic electron emission

Abstract: Kinetic electron emission by 12–30 keV ions ranging from Z 1 = 3 to 92 has been studied on clean gold surfaces. With the aid of an ion-electron converter the average electron yield and the emission statistics were measured. Pronounced oscillations of the yield with the shell structure of the projectile ion were found, suggesting a significant contribution of excitation processes of the projectile to electron emission.

Surface Dislocation of MgO(100) Studied by Secondary Electron Emission Spectroscopy and Cathodoluminescence Spectroscopy

Abstract: Surface electronic and vibrational properties of “fine” and “defective” MgO(100) surfaces have been studied by secondary electron emission spectroscopy applying the electron time-of-flight method and cathodoluminescence spectroscopy under ultra-high vacuum. The energies of the bottom of the conduction band and a level related closely to the F center in MgO are determined to be 4.0 and 1.6 eV above the vacuum level, respectively. Work function, which is the energy difference between the vacuum level and the top of the valence band, of MgO is determined to be 3.8 eV. In the “defective” crystal, the phonon side band due to electron-phonon coupling is resolved around the extra peak at 1.6 eV in the secondary electron emission.

Scanning type electron microscope

Abstract: In a field emission scanning type electron microscope which varies widely a primary electron beam acceleration voltage, a width of the primary electron beam is thinly focused by a large acceleration voltage when the beam passes through the focusing lens. The AC variation caused due to the gases near an electron source is included in the primary electron beam current. The variation of the primary electron beam which spreads near an objective lens after it has passed through the focusing lens is detected by a detector near the objective lens. The secondary electron beam emitted from a specimen is detected by a scintillator to produce a scanning measurement signal. When the acceleration voltage is large, the scanning measurement signal is divided by an output signal of a detector near the objective lens. When the acceleration voltage is small, the measurement signal is divided by an output signal of a detector near the focusing lens. This selection may be performed by means for selecting on the basis of a ratio R (=(acceleration voltage V 0 )/(lead-out voltage V 1 ) to be obtained from the high voltage source apparatus. Alternatively there may be provided comparator means for comparing the AC variations of the two signals which are obtained by dividing a scanning measurement signal by the signals of both detectors and selector means for applying the smaller signal to a display.

Localized field ion emission using adsorbed hydrogen films on 〈110〉‐oriented tungsten field emitters

Abstract: Growth of microstructures on the surface of thermally annealed 〈110〉‐oriented tungsten field emitters is reported to occur in association with local field electron stimulated desorption of physisorbed hydrogen films. Localized electron stimulated desorption of the hydrogen film and the simultaneous local increase of the electron emission to values greater than 104 A/cm2 activate surface rearrangement and the growth of microstructures in the region bounded by the film. Growth of a single 0.02‐μm‐wide structure by this means and imaging in a low‐field (1 V/A) regime of the field ion microscope provides a stable beam of hydrogen (H+2) ion current of 15 nA in half‐angular apertures of 0.016 rad.

fcc needle crystals of molybdenum grown from Mo(CO)6

Abstract: It is shown that fcc needle crystals vapor‐grown from Mo(CO)6 through a cathodic growth process are fcc polymorphs of Mo. Electron diffraction studies coupled with Auger spectroscopy revealed that the needles consist of randomly oriented single microcrystals, whose lattice constant, determined by electron diffraction, is 4.14 – 4.21 A. This is greater than the theoretically expected value. It is believed that this expanded fcc lattice is attributable primarily to the growth of the needles in a high electric field.

Microprocessor-aided remoulding of field emitters

Abstract: A device for remoulding tip-shaped field emitters is presented. It is described in the context of field electron emission, but many of its basic principles will apply to field ion emission as well. The system consists of two high tension cascades providing positive and negative high voltage, a device generating DC (constant or intermittent) for resistively heating the emitter, the microcomputer system and some additional protection circuits. First tests of the remoulding system in a simple field electron emission assembly are reported. A novel type of remoulding method is presented where the emitter is switched to field electron emission operation between heating pulses. This allows a better and faster control of the remoulding process. The normally desirable emission pattern consisting of only one single bright spot could be produced conveniently and quickly. Future possibilities for improving the system in terms of automating the remoulding process are discussed.

Field emission gun electrode geometry for improved focus stability

Abstract: In field emission systems having beam current regulation by use of modulating field strengths from a control or Wehnelt electrode adjacent the emission electrode, the varying field strengths produce a focus instability of the emitted beam. By the precise spacing of the emission tip, Wehnelt electrode and first accelerating electrode, and by the precise aperture diameters of the Wehnelt and first accelerating electrodes, the beam focus remains stabilized for modulating field strength variations.

Electron field emission from copper with various thicknesses of oxide film

Abstract: A new, nondestructive method for electron field emission measurement is presented, which, in principle, completely avoids the need for deleterious multiple sparking of the surface required by previous workers and which allows electron field emission to be measured at its origin; i.e. with only a few electrons leaving the cathodes per second. The results obtained on oxide-covered copper cathodes with various controlled thicknesses differ markedly from those obtained by previous workers and conform more with modern interpretation.

Field emission type electron microscope using a multi-stage acceleration tube

Abstract: A field emission type electron microscope using a multi-stage acceleration tube wherein an acceleration voltage to be applied to at least one, always inclusive of a first-stage acceleration electrode, of acceleration electrodes is changed in interlocked relationship with a change in a field emission voltage to be applied to a field emission electrode, so that power of an electrostatic lens can be kept constant.

Phonon Emission and Electron Heating in a Two-Dimensional Electron Gas

Abstract: The transport properties of two-dimensional electrons formed at the heterojunction of GaAs and AlGaAs has been the subject of intense experimental and theoretical interest over the last few years.[1] This interest has arisen because of the invention of modulation doping[2,3] which has led to spectacular improvements in the low-field, low-temperature mobility through the spatial separation of the current carrying electrons from their parent ionized donors. This mobility enhancement has been used to fabricate ultra-high speed field-effect transistors. The field dependence of the mobility[4] and the basic scattering mechanisms determining the mobility are, however, as yet imperfectly understood. Progress has recently[5] been made through the observation of photoluminescence spectra of modulation doped superlattices in the presence of an electric field. In this paper we report on complementary measurements made on a single interface by observing the energy relaxation of carriers by phonon emission. We correlate the phonon emission observed with changes in the mobility (μ) as a function of electric field (E). Earlier work[6] in this area involved phonon transmission through a super lattice which shows the ideality of MBE grown interfaces.

A study of the electric field dependence of subthreshold photoemission

Abstract: Experiments that detect electrons photoemitted from W(110) at energies below the vacuum level are reported. The data are obtained by performing energy resolved measurements of the electrons photoemitted from a tungsten field emission tip that is illuminated by focused UV lines from an argon–ion laser. Data on the final state energy distributions are analyzed by a theory that includes the transmission probability for an electron escaping from a metal–vacuum interface at energies below threshold. Data on the subthreshold photocurrent integrated over all final state energies reveal an oscillatory contribution when measured as a function of electric field. Fourier analysis of this data gives a frequency of (10.3±0.9)×104 (V/cm)1/2, a result that is in close agreement with previous measurements. The origin of this oscillatory structure has still not been conclusively established.