Showing papers in "International Journal of Electronics in 1959"

The Thermoelectric Figure of Merit and its Relation to Thermoelectric Generators

Abstract: The expression for the figure of merit of a semi-conductor of given carrier mobility and lattice thermal conductivity expressed in terms of generalized Fermi-Dirae functions has been numerically evaluated for various scattering indices. The results are presented graphically enabling the maximum figure of merit to be found. High-temperature limitations due to minority carrier production are considered in relation to the energy gap of the semi-conductor. The results are discussed in connection with bismuth telluride and other sulphides, selenides and telluridos of the heavy metals.

Factors Affecting Contrast and Resolution in the Scanning Electron Microscope

Abstract: (1959). Factors Affecting Contrast and Resolution in the Scanning Electron Microscope† Journal of Electronics and Control: Vol. 7, No. 2, pp. 97-111.

Magnetization Reversal by Rotation and Wall Motion in Thin Films of Nickel-Iron Alloys†

Abstract: The magnetization reversal process in specially prepared uniaxial thin films of nickel—iron alloy is studied by measurements of the 400 c.p.s. hysteresis loops. The results indicate that both coherent rotation and domain wall motion can occur in the same film, but in different proportions according to the orientation of the anisotropy axis with respect to the applied field and the thickness of the film. Special properties of these films are discussed for fields applied normal to the anisotropy axis.

The Behaviour of Linear Systems with Inputs satisfying certain Bounding Conditions

Abstract: Linear filters with bounded inputs give outputs which arc also bounded. A method is described for obtaining the least upper bound of the output for the case whore bounds are specified both for the magnitude of the input and its rate of change. The result, which is obtained in the form of a procedure for constructing that input (satisfying the bounding conditions) which gives riso to the largest output, has applications in the design of automatic control systems.

Evaporation of Barium from Cathodes Impregnated with Barium–Calcium–Aluminate

Abstract: The evaporation of barium from cathodes impregnated with barium-calcium-aluminate, 3BaO. Al2O3½CaO has been observed during the life of cathodes made with various thicknesses of two types of porous tungsten. The slow decay observed in thin cathodes of very porous tungsten appears to be duo mainly to the reaction producing barium being retarded by the reaction products accumulating at the interface between the tungsten and the impregnant. The more rapid decrease for thick cathodes of lower porosity is due to the escape of barium becoming the limiting factor. This results in the reaction going to completion at increasingly greater depths within the cathode during life. The transport of barium to the surface of the cathode appears to be mainly by migration along the crystal boundaries in the impregnant and reaction products.

Magnetic Deflection Focusing

Abstract: A scheme for focusing sheet, beams by means of a periodic configuration of magnetic fields directed transverse to the beam is presented. Discussion of a particular model gives information about stability limits and perveance. This scheme, which lends itself to the incorporation of intense magnetic fields, should be immune to the space-charge instabilities of beams focused in longitudinal magnetic fields. The focusing mechanism is such as to produce coupling between the beam and electromagnetic waves of phase velocity exceeding the velocity of light. Application to millimetre-wave tubes is anticipated.

Hole Conduction and Photovoltaic Effects in CdS

Abstract: Semiconducting crystals of CdS have been prepared in which the conduction current is carried preponderantly by positive holes. This is indicated by the positive sign of the Hall voltage and the thermoelectric power. The preparation of these crystals, which were heavily doped with 1–2% Cu, is described. Measurements of electrical conductivity, Hall coefficient and thermoelectric power over the temperature range 95-380°k are reported. The results are difficult to interpret, but suggest that conduction occurs via impurity levels due to copper. Similar measurements on some typical n-type semiconducting CdS crystals are reported for comparison purposes Some attempts have been made to prepare p-;n junctions in CdS. Appreciable photovoltaic effects have been found, and the spectral response and rectification characteristics can be explained in terms of a p-n junction model.

Breakdown in Silicon pn Junctions

Abstract: Some useful empirical relationships on the variation of effective ionization coefficients associated with the avalanche breakdown phenomena in pn junctions are derived from measurements on silicon alloy junctions, in the range of impurity concentrations of the basic material from 5 × 1013/cm3 to 10l8/cm3. These results show that for electric field strengths from 1.5 × 203 v/ cm to 3 × 105 v /cm the effective ionization coefficient is equal to 18E7; from 3 × 10 7 v/cm to 6 × 105 v/cm it is of the form 2.7 × 10 5 exp–(6.45/E) and for values greater than 6 × 105 v/cm the effective ionization coefficient tends to E 105/5 where in all cases E is measured in units of 105 v/cm. Some discussion is given on the compatibility of calculations of ionization coefficients derived from breakdown measurements and those from multiplication measurements.

The Electrical Conductivity and Hall Coefficient of Bismuth Telluride

Abstract: This paper describes the variation of the electrical conductivity and Hall coefficient of a number of specimens of Bi2Te3 over a wide range of doping concentration. A detailed examination of these quantities, over the temperature range 1-3 to 660°K, has revealed the oxistence of trends which vary systematically with the degree of doping, although anomalies oxist within this scheme. It is shown that an impurity band mechanism may operate in n-type Bi2Te3.

Field Effect at High Frequency

Abstract: The paper develops the theory of the field effect at high frequencies, using the same basic assumptions as Garrett (1957), with more complete conditions at the back surface. The charges induced in the front surface layer are given as the sums of two terms, of which one depends on the surface properties only, and the other is proportional to the modulation of the carrier density at the boundary between the surface layer and the bulk, which depends on the filament lifetime. The results are illustrated in detail by e numerical example.

Potential Distribution between two Plane Emitting Electrodes

Abstract: This paper gives the derivation of expressions for the space charge and potential distribution between two plane parallel emitting electrodes. Numerical calculations are carried out for the case when an external potential difference φext is applied between the electrodes, both being at the same temperature T. It is shown that all possible potential distributions can be represented by a single family of curves, the parameter of the family being.A=(—eφext/kT). Thus for a given φext the same general curve of potential distribution applies, whatever the values of the electrode work functions. Changing the work functions merely shifts the end points of the potential distribution along the curve.

The Poisoning of Impregnated Cathodes

Abstract: The poisoning of barium— calcium aluminate impregnated tungsten cathodes by various gases has been investigated experimentally It is shown that oxygen, water vapour, carbon dioxide and air poison these cathodes, while carbon monoxide, nitrogen and hydrogen do not Poisoning takes place with the former gases if a critical pressure, depending on the gas is exceeded, this pressure increasing with cathode temperature For a normal operating temperature of 1100° c the approximate critical pressures for the gases are as follows: O2 10−1mm, H20 3x I0−6 mm, C0210−6mm and air 5 x 10mm Cathodes with two different porosities of tungsten show somewhat different poisoning characteristics The amount of poisoning increases rapidly with the pressure when once the critical pressure pois exceeded, an equilibrium value of the emission poisoning ratio dependent on plp0 being reached For very severe poisoning, tho reactivation time increases with the time the cathode has been held in the poisoned condition, but f

A Reliable Method for the Production of High Purity Indium Antimonide

Abstract: Principles described previously have been applied to the production of the semiconducting compound InSb, conveniently and reliably, with uncompensated donor densities of about 1014/cm2. Details of the apparatus and method are given, and the factors limiting the purity to this level are considered.

New experimental results for plasma electron oscillations

Abstract: This paper contains an account of some experimental investigations of plasma electron oscillations in low-pressure mercury vapour discharges with plane oxide coated cathodes. The appearances of some of the discharges are described. The primary electrons were deviated laterally in or near the meniscus-shaped region of ionized gas brighter than the surrounding plasma, which appeared a few millimetres from the cathode. Variation of anode-cathode separation was found to have a marked effect on both the appearance of the deflected beams and the meniscus, and on the high-frequency oscillatory properties of the discharges. Measurements of plasma electron concentration and temperature were made simultaneously with measurements of oscillation intensity and frequency. A strong tendency was found for the oscillations to grow in amplitude when the beam of primary electrons moved down a concentration gradient and to die out when the beam moved up a gradient. The frequency of the oscillation was found to agree...

Transition Probability Densities of the Smoothed Random Telegraph Signal

Abstract: In a previous paper (Wonham and Fuller 1958) the steady-state probability density of output was derived for a low-pass JRC filter driven by a random telegraph signal. In the present paper the earlier result is extended by the derivation of the transition probability functions of the associated Markov process.

Turn-on Transient of p-n-p-n Triode †

Abstract: The turn-on transient of the p-n-p-n switch is analysed with simplifying assumptions. Experiments on the silicon p-n-p-n power triode show that the two mechanisms determine the current waveform during the transient. Before the centre junction becomes forward biased (switches on), the current increases nearly (or faster than) exponentially. After switch-on, the p-n-p-n switch behaves as an inductive impedance and the increase rate of current decreases. This is ascribed to the gradual modulation of conductivity of a base region of high resistance. Analytical expression is derived for the relation between base current and delay time when the step current is applied to the base.

PLASMA CONTAINMENT BY r.f. AND d.c. FIELD COMBINATIONS

Abstract: An investigation has been made concerning the use of radio frequency fields for the containment of hot, dense plasmas, such as those needed for controlled thermonuclear fusion. Because high losses due to skin effect are associated to r.f. fields, they will be used at the lowest possible frequency, and only where they constitute a useful supplement to the cheaper d.e. fields. Such r.f. fields are to be useful for reducing the plasma leakage present in most d.e. confinement systems, and to prevent some of the instabilities inherent to d.e. systems. One particular combination of d.e. and r.f. fields has been analysed in detail. It consists of a homogeneous axial d.e. magnetic field (or a d.e. mirror field) containing a plasma column against radial diffusion; the ends of the column are ‘ sealed ’ by moans of r.f. fields. By using the proper polarization of the r.f. fields, it is shown that appreciable plasma pressures can be contained, using r.f. fields of frequencies as low as a few megacycles. By u...

The Faraday Effect in Anisotropic Semiconductors

Abstract: The theory of the Faraday effect in semiconductors is extended to uniaxial crystals with spheroidal energy surfaces, using the classical Drude-Zener theory. Expressions applicable at infra-red frequencies are given and used to discuss preliminary measurements on Bi2Te3

Fast Wave Couplers for Longitudinal Beam Parametric Amplifiers

Abstract: The theory and design for fast wave helix couplers for use with longitudinal beam parametric amplifiers are given. The TWT equations are put in coupled mode form. A matrix formulation of these equations is used to point out a formal mathematical analogue of the Schrodinger equation of quantum mechanics. This analogue is used to suggest possible techniques of solution and may lead to hitherto unexplored methods of treating this problem. Two special eases are treated. The formulation is equivalent to that used by Haus and Robinson (1954). The design procedure for fast wave couplers is given in detail in a separate section. The coupler consists of a Kompfner dip helix preceded and followed by a velocity jump. By this technique it is shown that a fast space-charge wave can be excited on the beam. The fast mode noise can be completely removed from the beam by the same coupler. The slow mode goes through completely unaffected in amplitude. Since the slow mode is not amplified, noise from the slow mode ...

Some Solutions to the Equations of Steady Space Charge Flow in Magnetic Fields

Abstract: The equations for steady, laminar, space charge flow are set. up. Sets of particular solutions in prescribed magnetic fields are presented— even when the magnetic field has components perpendicular to the cathode. Flows in a large class of magnetic fields from cylindrical and conical cathodes are shown to result, and the existence of similar flows from spiral sheet cathodes are mentioned.

A Modification of the Theory of the Variation of Junction Transistor Current Gain with Operating Point and Frequency

Abstract: A modified solution is discussod of the continuity equation for minority carrier flow in junction transistors, obtained by adhering strictly to the space-charge neutrality approximation and applying alternative boundary conditions which differ from those usually taken principally in that a finite minority carrier density is permitted at the collector. An extension of the modified analysis to a.e. conditions is given, and a comparatively short working formula for the intrinsic short-circuit a.c. gain is determined as a function of operating point and frequency. The common-base cut-off frequency f αs evaluated, and the maximum in the variation of the f αwith emitter current, which has been observed experimentally, is associated with reduced d.c. emitter efficiency at high levels and is related to the corresponding fall-off in d.c. alpha. Experimental results are presented to show that, for a transistor with given cut-off frequency, both the electrical and metallurgical base widths are smaller than ...

Theory of the Focusing of Sheet Beams in Periodic Fields

Abstract: Equations determining the paraxial behaviour of sheet beams in periodic focusing fields are established. Space-charge is taken into account, and its effect upon stability is investigated. It is proved that, if space-charge is neglected, any such focusing system is convergent. A procedure for determining optimum lamellar-flow configurations is set out, and approximate formulae for the perveance of such focusing systems are presented.

Similitude and Anode Material Effects in H2 and D2 Discharges Below the Critical Pressure

Abstract: The breakdown potentials of H2 and. D2 gases were determined below the critical pressure in two discharge tubes of similar shape but of different size in order to ascertain whether or not the initi...

A Three-Frequency Electron Beam Parametric Amplifier and Frequency Converter†

Abstract: The principle of varying a circuit reactance to produce gain is applied to an electron beam. The beam is modulated by an r.f. wave at frequency ω and this supplies energy to a signal at frequency ω1 and an idler at frequency ω2 which is generated in the beam, where ω = ω1 ± ω2 is found that when ω1 + ω2 the signal idler grows exponentially while if ω1 − ω2 power is continuously converted from ω1 to ω2 and back to ω1. For finite size beams, a current modulation threshold must be exceeded to produce growing waves. For the zero thickness beam no such threshold is observed. The growing waves are found to be fast space charge waves for a range of values of the signal to idler frequency ratio in contrast with conventional amplifiers which amplify slow waves and it is the latter class to which minimum noise figure theorems apply. Tho Manloy—Rowe relations are verified for the parametric beam and the gain per unit length is found analytically. Finally, boundary conditions are applied. It is found that wh...

The Effect of the Inclination of the Focusing Electrodes on Electron Beam Formation

Abstract: The behaviour of an electron-gun in which the ‘ Pierce electrodes ’ meet the cathode at an angle differing from (90 + 67½)° is investigated. The beam edge no longer emerges normally from the cathode and the current density at the periphery of the cathode is found to depend critically on the electrode angle, in agreement with previous experimental results.

The Effect of Field Configuration on Gas Discharge Breakdown in Microwave Cavities at Low Pressure

Abstract: A new regime of high-frequency gas discharge breakdown in non-uniform fields at low pressures is predicted on theoretical grounds and experimentally confirmed. The controlling mechanism is the time-averaged Lorontz force on the electrons, proportional to the gradient of the square of the electric field amplitude (∇|E|2). This steady force is derivable from a potential, and field configurations are realizable in microwave cavities corresponding to potential hills or wells, exemplified by E 010 and E 011 cylindrical cavities respectively. In the former case the steady force acts to disperse electrons towards the walls, increasing the loss of electrons and raising the breakdown field, whereas in the latter case the steady force acts to confine electrons, inhibiting electron loss and lowering the breakdown field. The effect becomes marked at levels of field intensity for which the height of the potential hill or well becomes comparable with the ionization energy. Breakdown fields have been measured f...

Chemically Deposited NiCo Layers as High-speed Storage Elements†

Abstract: Layers of NiCo have boon prepared by chemical reduction and their possible application for high-speed memory elements has boon examined. Switching constants of 0·15 μsee oersted have been achieved on layers with domain wall coereivities of about 2 oersteds and the process appears to give reproducible results. The method is simple and inexpensive and should be adaptable to the production of storage elements in largo numbers.

Approximation Errors in Diode Function-generators †

Abstract: Errors in electronic function-generators using biased diodes comprise (i) ‘ electronic ’ errors due to amplifier drift, diode characteristics, etc, (ii) ‘ approximation ’ errors resulting from fitting a piecewise-linear function to a smooth curve Errors of type (ii) only are discussed here It is shown how, using either of two obvious criteria for a ‘ best ’ fit, the relationship between error and number of segments is obtained from a simple integral, to within the accuracy normally required in analogue-computer applications ; the same integral is used to calculate the breakpoints between segments Formulae and numerical results are given for some typical functions