Showing papers in "Advances in electronics and electron physics in 1982"

A Dynamical Radiation Model for Microstrip Structures

Abstract: Publisher Summary This chapter deals with the models currently used to improve the quasistatic approximation of microstrip structures. The chapter presents a brief review of the microstrip fundamentals; a comprehensive account of these dynamical models. A particular model based on the calculation of the electric surface currents in the structure is introduced in the chapter. The Green's functions involved are constructed and numerically evaluated using the exact formulation for dipole potentials in a stratified medium. New evaluation techniques developed for Sommerfeld integrals permit a very accurate computation of Green's functions. Their properties are then extensively discussed; the validity of the quasistatic approximations is checked and the importance of the surface wave is pointed out in detail. Finally, the integral equations for the currents are set up and solved by numerical methods in that also give several practical applications. The chapter concludes the model is that the surface currents on the antenna are directly determined and the near field can then be determined easily, that becomes most important when microstrip structures are utilized as radiators or biological applicators.

Point Defects in GaP, GaAs, and InP

Abstract: Publisher Summary This chapter presents an overview of the experimental investigations of point defects in gallium phosphide (GaP), gallium arsenide (GaAs), and indium phosphide (InP). It divides the experimental methods suitable for defect investigations into destructive, impurity element-specific, nondestructive, and defect-specific techniques. Among the impurity element-specific, mass-spectroscopy, atomic absorption, and nuclear methods like neutron activation analysis are the most important, as they provide information about the total impurity content of a specific element. Defect-specific techniques are grouped into four categories: electrical, optical, magnetic, and nuclear. The chapter outlines some general aspects of these techniques. It mentions that the standard semiconductor assessment techniques, resistivity and Hall-effect measurements, are indispensible tools to establish the electrical properties of shallow donors and acceptors. Special emphasis is given to deep-center identification. The chapter reveals that donors and acceptors are mostly deliberate dopants enabling n- or p-type conductivity of the crystal. Donor states are created by group VI elements on anion (P, As) sites as well as by group IV elements on cation (Ga, In) sites. Correspondingly, acceptor states are formed by electron-deficient dopants— that is, by group II elements on cation sites and by group IV elements on anion sites.

Holography in Electron Microscopy

Abstract: Publisher Summary The chapter introduces a new method called holography, the actual purpose is to invent an electron optical device able to produce strongly magnlfied images, the aberrations of that can be eliminated afterward by light optical processing. The shadow electron microscope of Boersch can be used for the electron optical step. The optics of this system is identical with that of a modern scanning transmission electron microscope, using a fixed and slightly defocused electron probe. The chapter reveals that the electron holograms can be taken in a conventional electron microscope by applying large defocusings. The chapter presents the survey of the Fourier optical transfer theory. In the course of these considerations, it has become clear that the range of application of Gabor's method is restricted either to pure weak amplitude objects or to pure weak phase objects. The extension of this method to strong objects, however, is not possible and the problems are discussed in the chapter. The problems connected with off-axis holography are also discussed. The chapter explains that the object and reference waves in the electron microscope is created by splitting the illumination wave, using an electrostatic biprism. But in close analogy to the current light optical reconstruction methods, object and reference waves can also be generated by means of a scattering foil, and the interferometric method employing amplitude splitting by crystal diffraction instead of wave front splitting was recently brought to a successful conclusion by Matteucci. The chapter deals with recent investigations in this field.

Collisional detachment of negative ions

Abstract: Publisher Summary This chapter discusses the process of collisional detachment of negative ions, in which negative ion collides with a neutral atom or molecule producing a free electron. This process is a principal mechanism for the destruction of negative ions and is frequently the dominant inelastic collision channel for negative ions. The chapter presents the examples of various mechanisms that can lead to the collisional detachment of negative ions for energies ranging from below the threshold for detachment up to several hundred kilo-electron volts. A qualitative discussion of these experimental observations for low collision energies has been based primarily on the features of the intermolecular potentials for the negative ion-atom reactants. For the simpler reactants, there are several theoretical approaches that have been used to describe the dynamics of the discrete-continuum interaction associated with direct detachment. The chapter demonstrates that direct detachment almost always dominates the inelastic scattering in collisions of the negative ions with atoms or molecules.

Stimulated Ĉerenkov Radiation

Abstract: Publisher Summary This aim of this chapter is to establish the criteria necessary for producing usable levels of stimulated Cerenkov radiation at short wavelengths compared to the characteristic scale length of both the transverse and longitudinal dimensions of a dielectric resonator The electromagnetic wave produced by a charged particle moving faster than light in a dielectric medium is known universally as Cerenkov radiation A number of experiments are designed to explore the properties of Cerenkov radiation produced by prebunched electron beams moving in close proximity to a dielectric surface The chapter discusses the use of the combination of the electron beam and the dielectric resonator to generate coherent radiation in the millimeter through infra-red (IR) portions of the electromagnetic spectrum It describes Cerenkov maser, which is a device consisting of a dielectric resonator, an electron beam, and an output coupling structure Special emphasis is given on resonators that are separate from the beam A series of calculations aimed at establishing the current beam energy, and velocity spread required to obtain the growth of stimulated Cerenkov radiation is presented The chapter examines the exponential gain of stimulated Cerenkov radiation obtained when it is assumed that either a strongly magnetized or a completely unmagnetized monoenergetic electron beam passes directly through a dielectric medium The limit implied by the assumption that the beam is monoenergetic is also examined and modified gain formulas are derived

Aspects of High-Field Transport in Semiconductor Heterolayers and Semiconductor Devices

Abstract: Publisher Summary This chapter focuses on the new developments in the general area of high-field transport, and is also intended to provide a bridge in the information gap between scientists working on device modeling and others working on the basic physics of hot electrons. The most important elements of transport have been reviewed and some simple applications to devices, such as, diffusion, space-charge-limited current, etc., have been shown. Special emphasis has been put on transport in heterolayers and at interfaces. The chapter explores the band structure on electronic transport at high energies. The problem areas are specifically addressed in the chapter. The review also compares III-V compounds, especially GaAs to silicon, and an attempt is made to assess the advantages and disadvantages of device operation from a theoretical viewpoint. It is shown that with respect to speed and variability due to boundary conditions, lattice-matched heterojunctions and III-V compounds are far superior to silicon. The chapter presents the future generations of III-V compound devices that may compare to silicon like small aircraft to long freight trains. The chapter presents an account of transport parameters at interfaces. The transport processes themselves are treated in the chapter.

Modeling of Irradiation-Induced Changes in the Electrical Properties of Metal-Oxide-Semiconductor Structures

Abstract: Publisher Summary This chapter discusses the characteristics of metal-oxide semiconductor (MOS) devices. It models the transient behavior of MOS structures for applied voltage step functions and calculates the resulting distributions of charge in the oxide. The results of this model are modified and applied to cases where various quantities of ionizing radiation are absorbed in the oxide for a wide range of applied gate biases. The details of the model and the resulting conclusions are presented. Two types of observables— namely, direct observables and indirect are discussed to determine the effects of irradiation on MOS structures. Direct observables can be monitored directly either during or after termination of each irradiation increment, whereas indirect observables cannot be observed without additional irradiation increments and/or processing of the device. The chapter reviews two simple descriptive models as accurate representations of irradiated MOS structures: captured during transit (CDT) models and dynamic equilibrium (DE) models. It deals with the complete computer simulation of MOS system.

Rydberg Atom Collision Processes

Abstract: Publisher Summary The chapter focuses on more recent experiments in the atoms in single, well-defined Rydberg states are employed. The theoretical approaches employed differ from those used for treating interactions involving atoms in ground or low-lying excited states; the latter utilize, in essence, a molecular approach in that potential curves or surfaces are determined for a small number of electronic states as a function of internuclear distance and these, and the coupling matrix elements between them serve as an input to a scattering calculation. Many of the theoretical approaches used to treat interactions between Rydberg atoms and charged particles, and their ranges of validity, have been reviewed in the chapter and present the collisions with atoms, molecules, and charged particles. Studies of collisions between Rydberg atoms, and either neutral or charged targets have revealed a wide variety of novel collision processes, many of that have enormous cross sections. The chapter concludes that further studies are required, for example, to determine how the collision processes depend on the angular momentum of the Rydberg electron and to elucidate the role of the core in collisions.

Materials Considerations for Advances in Submicron Very Large Scale Integration

Abstract: Publisher Summary This chapter introduces the submicron metal-oxide semiconductor field-effect transistor (MOSFET) and examines the operation of submicron MOSFETs and junction field-effect transistor-metal semiconductor field-effect transistor (JFET-MESFETs). It presents the requirements for switching high-speed logic. It reviews the band structure variation for silicon and the relevant III-V compounds. The theory of random alloys and the band parameter variations, both for ternary and for quaternary alloys, is discussed. The comparison between silicon and various III-V technologies is drawn for devices in the extreme submicron region— that is, devices of 0.1-0.2 μm gate length. The chapter introduces the problem of line-to-line parasitic capacitance. For device sizes in the 0.12- μm or less region, the line-to-line parasitic capacitance begins to dominate the direct-line capacitance in setting the node capacitance. The chapter concludes that the devices fabricated from materials, such as gallium arsenide (GaAs) and indium phosphide (InP) offer definitive speed advantages over silicon circuitry. The ternaries and quaternaries offer no advantage over InP in comparable devices, and are severely restricted in packing density by their exceedingly poor value of thermal conductivity.

Ion Implantation for Very Large Scale Integration

Abstract: Publisher Summary This chapter describes ion implantation for very large scale integration (VLSI). For VLSI circuits, extremely shallow highly doped layers with a low lateral spread are required. Ion implantation for doping applications always requires a high-temperature treatment to anneal the radiation damage produced by the implantation itself. The chapter presents the theoretical considerations concerning range profiles, lateral spread, sputtering, knock-on, and molecular implantation and compares them to experimental results. During implantation, many crystal defects are produced. At high doses, amorphous layers can also form. A temperature treatment is required to anneal out these defects and to render the implanted ions electrically active. The chapter describes the annealing of implanted layers including damage with additional attention to diffusion, segregation, and some problems concerning process modeling. It discusses the dependence of the annealing process on temperature, orientation, doping concentration, and atmosphere. It also discusses non-doping applications of ion implantation and presents some device applications, demonstrating the superior possibilities of ion implantation.