The effect of tolerances in conical flow Pierce guns I—The perturbed flow within the gun

A first-order perturbation analysis of the dc effects of several important tolerances in conical flow Pierce guns is presented for the case in which the gun is part of a solenoid focused system used to produce a smooth Brillouin beam. In this, the first of two parts, the flow up to the anode of the gun is analyzed. The data presented permit calculation of the magnitude of the perturbations at the anode due to various manufacturing errors. These errors are: changes in cathode-anode spacing, changes in cathode curvature, tilt, and transverse displacement of the cathode-focus electrode assembly. The theory does not permit the analysis of cathode to focus electrode tolerances. The perturbations at the anode serve as boundary conditions for the flow beyond the gun which is calculated in the companion paper. A comparison of the magnitude of effects at the anode calculated by the theory and obtained from an experimental study shows that reasonably good agreement exists between theory and experiment.     

The grid lens effect in convergent Pierce guns

In a conventional Pierce-type gun, the anode aperture causes a potential reduction in the cathode-anode region from the ideal Langmuir potential distribution. For low-voltage gating of the electron beam, a mesh grid of spherical shape (conforming to an equipotential surface) is used in front of the cathode. When this grid is operated at the Langmuir potential depicted by its relative position, there is a difference in the potential gradients on its two sides. This difference causes a lens action at each mesh element which results in a displacement of the actual electron trajectory from the ideal laminar trajectory in the region beyond the anode. A means for calculating these displacements as a function of distance along the axis is developed. As the grid lenses are divergent, the images of the mesh elements in any plane beyond the anode are larger than those for ideal laminar flow, resulting in a current density distribution which differs from that of the ideal beam. A means of calculating the current density profile by summing the effects of the grid lenses is devised, and the method is applied to a sample gun design to illustrate the effect on the current density distribution.     

Thermal properties of the Burrus-type light-emitting diode: Part II—The results

The results of an exact three-dimensional thermal model (shown in the first part of the work) of the Burrus-type light-emitting diode are presented in the present paper. The influence of various construction parameters of the homojunction GaAs Burrus-type LED on the temperature distributions in its active region is discussed. Thermal properties of the double-heterostructure GaAs-(AlGa)As Burrus-type LED are explained. The heat-spreading phenomenon in the heat sink of the diode is analyzed.     

Dispersion relations in time-space periodic media part II—Unstable interactions

The conditions sufficient to assert the existence of absolute (time-growing) instabilities in distributed parametric structures or media are shown. Treating the simple, linearized, time-space periodic transmission line model, it is shown that time-growing instabilities exist in an unbounded medium whenever the pump modulation velocity is greater then the characteristic velocity of the medium and is in the convergent ("nonsonic") range of operation. The existence of these instabilities is based upon the rigorous calculation of the dispersion relation for the model, accounting for all small-signal frequencies. Proof of the existence of the instability, using the dispersion relation of the active structure, is based upon the method of Briggs, previously used in electron-stream interactions. The waveform of these instabilities is that of the backward-wave oscillator and comparisons with backward-wave oscillator (electron-beam) tubes are made. The predictions of the theory hold only for the transient period, for which the linearized model is valid, before the fields reach the nonlinear regime. The analysis, however, forms the basis for certain simple calculations of oscillation frequency, growth rates, predictions of competing interactions, and identification of wave types--all useful for application. The method of analysis should be useful for application to various other types of parametric interactions involving elastic waves, spin waves, plasma waves, etc., in single or multimode coupling schemes. The frequency range of application of such traveling-wave parametric effects extends from the optical range down to the radio-frequency range.     

The photovoltaic effect in the Cu—Cd—S system

Models of the photovoltaic cell proposed by various authors are subjected to a critical examination to isolate their underlying assumptions and to devise possible experimental tests of the models. The results of an investigation of a model in which the Cu2S layer plays an active role are presented. These include a calculation of spectral response and a comparison of calculated and measured spectral response curves; an electron microprobe study whose conclusion is that the Cu2S layer is thinner than 0.5 µm; a discussion of the crossover of dark and lighti-Vcharacteristics and a test of whether this shift is adequately explained by an internal series resistance; and a study of the effects of low-energy proton irradiation on the properties of Cu-Cd-S cells.     

Video detection of millimeter waves with glow discharge tubes: Part I—Physical description; part II—Experimental results

An experimental program was undertaken with the goal of realizing a fast, inexpensive millimeter wave glow discharge video detector. The work performed led to the realization of an economical commercial glow tube that, when biased properly, exhibits a sensitivity quite comparable to that of the crystal diode detector. As a result of this work, an anomalous mode plus a new mode of detection utilizing a sensing electrode external to the glow tube, with considerable improvement in NEP, were observed. In this paper, Part I describes the detection mechanism and physical characteristics of a glow discharge found to be important in the detection of millimeter waves and Part II the results of experiments concerning effects of biasing and gas type and pressure upon sensitivity.     

Semi-empirical equations for electron velocity in silicon: Part II—MOS inversion layer

We present a simple model of inversion layer and accumulation layer mobilities in Si MOSFET's. The use of an effective normal field and a simple approximation for the temperature dependent quantum mechanically broadened channel layer width Permits the development of a versatile semi-empirical equation. This equation provides good agreement with electron mobility data in the literature as a function of normal electric field, temperature, substrate doping, and fixed charge density. Screening effects have considerable influence in the model. Subthreshold behavior is predicted with reasonable accuracy. The model is also applicable at high tangential fields where mobility is reduced due to hot-carrier effects.     

Electron motion in a helically perturbed magnetic field

Exact solutions have been obtained for the equations of an electron subjected to a transverse rotating magnetic field superimposed on a homogeneous axial magnetic field. The solutions show that complete transfer of the axial energy into transverse energy is possible for a range of values of the injection velocity and the transverse magnetic field.     

Demodulation of low-level broad-band optical signals with semiconductors: Part II—Analysis of the photoconductive detector

A fast response photoconductor with a high frequency bias supply is considered as an envelope detector for optical signals. The sensitivity is studied and compared with that of the diode demodulator. The ratio of SNR for the two devices is equal to the photocurrent gain. It is shown to be theoretically possible to achieve enough current gain to overcome the noise of the following amplifier. The current gain comes from two effects. One is a true photocurrent gain in the semiconductor itself, which can exceed unity if the microwave field reverses before the photocarriers are swept out. It can be as high as the number of times the photocarriers traverse the photoconductor before they recombine. The impedance transformation from the high resistance of the detector to the amplifier input gives additional current gain. Analysis of gain-bandwidth limitations reveals no restriction imposed by material parameters, in contrast to the case of dc bias. With RF bias, blocking contacts to the crystal are useable and the relationship between material resistivity and gain-bandwidth avoided. The limiting parameters are the signal bandwidth and the bias supply frequency, the device current gain being limited to the square of the Q value of the circuit. The effect of G-R noise is also considered and conditions derived under which it is unimportant. The two cases of a photoconductor in a rectangular waveguide and in a cavity are studied in more detail, and design equations relating sensitivity to the material and to the circuit parameters are deduced. For bandwidths up to at least 1 kMc, the photoconductor in the cavity can greatly outperform the photodiode. Its sensitivity can approach that of the photomultiplier with a high efficiency cathode, which opens the possibility of extending this high performance into the infrared.     

Harmonic analysis of periodic discontinuous functions (new method). Part II—Polynomial functions

A new method to determine Fourier coefficients of periodic discontinuous polynomial functions is presented. A method recently developed for exponential functions can be modified and applied to polynomial functions. Applications of the method is illustrated by example.     

Two-dimensional current flow in the MOSFET source—Drain

Series resistance within the metal-oxide-semiconductor field-effect transistor erodes some of the performance improvement inherent to channel length reduction. The subject of series resistance, then, assumes greater importance as transistor dimensions shrink. Since current crowding effects at the source-drain ohmic contact and at the junction of the source-drain and the channel increase the apparent series resistance, we have studied current flow and its associated nonuniformity by two analytical solutions of Laplace's equation with appropriate boundary conditions. We show typical results of these solutions, discuss the effect of device scaling on the current flow, and present simulation data for the self-aligned silicide field-effect transistor. The implicit assumption that the ohmic contact and source-channel current crowding contribute independently to the apparent source resistance fails for these self-aligned silicide devices.     

VLSI—The technological giant—And the developing countries

At a time when developing nations, after centuries of drift, are in search of an appropriate technology, they are confronted with a technological giant-Very Large Scale Integrated (VLSI) Circuit Technology-which seems to be gripping various aspects of the industrial sector and areas of human activity in the developed nations. In VLSI, the latest happens to be the most appropriate technology. The developing nations are yet to decide how appropriate and sustainable the VLSI technological edifice is in the context of their urge for modernization and the problems of an unemployment explosion, weak technological and scientific infrastructure, rural and agricultural bias, etc. The author believes that the developing countries will be involved in repeated technology transfer from developed nations in the area of VLSI through systems related to industry, defense, communication, instrumentation, etc. The various options of VLSI technology acquisition have been analyzed with their attendent problems. Downstream applications of VLSI to problems characteristic of developing nations, education and training in hardware and software, silicon foundry to serve as a technological listening post, and customdesign capability are some of the possible short-and long-term options for the developing nations to make optimum use of VLSI.     

The effect of the base—collector potential spike on the common-emitter I—V characteristics of AlGaAs double-heterojunction bipolar transistors

Knee-shaped common-emitter current-voltage characteristics are always observed on AlGaAs double-heterojunction bipolar transistors and phototransistors when a potential spike is present at the base-collector heterojunction and the spike height is bias-dependent. This phenomenon is explained successfully using a new transport theory that is based on the current-balancing concept. In addition, many important heterojunction parameters, such as the potential spike height and the p-n junction position with respect to the metallurgical junction, can be extracted. These parameters provide a valuable means of evaluating the initial growth condition of the heterojunction during the epitaxial process. On the other hand, the transport mechanism of nonequilibrium electrons injected over the heterojunction is modeled using a simplified random-walk process. Its effect on the common-emitter current-voltage characteristics is presented.     

Status of the GaAs metal—oxide—semiconductor technology

A review of recent and current work on GaAs insulated-gate technology is presented. First, various techniques for the formation of heteromorphic and homomorphic dielectrics are outlined and some important aspects of properties of these dielectrics are reviewed. Second, MOSFET structures, fabrication procedures, and microwave performance are described. Third, the application of GaAs MOSFET's to digital integrated circuits is summarized.     

Properties of ion-implanted junctions in mercury—cadmium—telluride

The formation of n-p junctions by ion-implantation in Hg0.71Cd0.29Te is shown to be a result of implantation damage. n-p photodiodes have been made by implantation of Ar, B, Al, and P in a p-type substrate with acceptor concentration of 4 × 10¹⁶cm^-3. The implanted n-type layer is characterized by sheet electron concentration of 10¹⁴to 10¹⁵cm^-2and electron mobility higher than 10³cm². V^-1. s^-1, for ion doses in the range 10¹³-5 × 10¹⁴cm^-2. The photodiodes have a spectral cutoff of 5.2 µm, quantum efficiency higher than 80 percent, and differential resistance by area product above 2000 Ω . cm²at 77 K. The temperature dependence of the differential resistance is discussed. The junction capacitance dependence on reverse voltage fits a linearly graded junction model. Reverse current characteristics at 77 K have been investigated using gate-controlled diodes. The results suggest that reverse breakdown is dominated by interband tunneling in field-induced junctions at the surface, for both polarities of surface potential.     

The transition field on the surface of a slot-excited conical antenna

A previous derivation of the transition field on the surface of a slot-excited conical antenna is corrected, and the new result as well as the tip-diffraction coefficient are checked by a calculation involving only the exact normal-mode series.     

The computer in education—Some examples

Educational institutions are now beginning to develop projects and programs, and to find the people to carry out both administrative and instructional activities which involve computer technology. The examples in this paper cover a broad spectrum of activity in handling information which is important to educational decision makers--the teacher, the guidance counsellor, the principal, the administrator--relating to the allocation of resources, to the effectiveness of educational programming, and to learning more about the process of education itself. Included in the paper are a discussion of the Palo Alto School District Educational Data Services operation and an explanation of the developing regional data processing concept in California. Later, the notion of the Computer Utility Data Bank is explored in terms of the present and future state-of-the-art as they are related to educational applications. Finally, the relationship of information to the user outside of the formal instructional situation (in the school) is considered in the light of new styles of urban planning and the total communications requirements which may be suggested for the user's home. The focus here is on Columbia City, Md. This sampling, and it can only be that, should suggest that a major revolution is in the offing. It will change our notions of how people learn, of what information is required for the meaningful life and for the contributing and participating citizen. As with other disciplines, the dialog between the educator and the computer scientist has barely begun.     

Influence of mechanical tolerances on field quality in the LHC maindipoles

We evaluate the influence of mechanical tolerances in the field quality in the LHC dipoles. We show that the most relevant effect is due to tolerances on the coil and on the internal part of the collars. The sensitivities of the field error multipoles on the mechanical tolerances are worked out using a finite element model of the dipole cross section. A Monte Carlo method is used to simulate the overall effect of both collar and coil tolerances on field quality. Correlation between random multipoles is worked out, and a comparison with the target table of the LHC field errors is given     

Effects of the induced magnetic field on the magnetohydrodynamic channel flow

The effects of a nonuniform magnetic field on magnetohydrodynamic (MHD) channel flow between two parallel plates of infinite extent are investigated. Influence of the induced magnetic field, such that the magnetic Reynolds number is less than unity but greater than zero, is included. The goal is to use the MHD effects to reduce the amount of heat transfer from the fluid to the channel walls. Expressions for distortion in the magnetic and flow fields are obtained. A solution is then obtained using the perturbation theory in the expansion of the field components in a double-power series in RmandI. The pressure gradient along the channel wall is examined. A criterion is developed under which Rmmust be taken into account in determining the heat transfer between the fluid and the channel walls.     

Transport of noise fluctuations in convergent flow crossed-field electron guns

The transport of noise fluctuations in convergent flow or so-called Kino-type crossed-field electron guns is investigated in terms of a two-dimensional computer simulation of the gun by the well-known Monte Carlo method for studying stochastic processes. The exact electrode configurations are simulated in the computer memory. After sufficient time has elapsed for the electron flow to achieve a steady-state condition 2000 additional time intervals are computed and then a statistical analysis is made of the fluctuation quantities. Six emission spots are considered on a finite-width cathode. The analysis is facilitated by the development of a rapid method for the solution of Poisson's equation (two-dimensional). Of particular interest in the results is the improved laminarity of the flow in the KG-M gun and the fact that there is significant space-charge smoothing throughout the gun region in both Kino-type guns. Of greater significance and as yet not explainable is the fact that Ψ versus ωct has local peaks when the space-charge density, which is spatially varying, passes through the Brillouin value (ω_{p}-ω_{c}for this condition). This knowledge could be profitably used in deciding on the location of the gun exit plane. The fact that the laminarity of the flow is sensitive to slight changes in the electric field near the cathode indicates that an absolute evaluation of the noise performance of KG-A and KG-M guns is difficult and may only be obtained through appropriate experiments.