Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 251-266).

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: C. Grant Willson. Vita. Includes bibliographical references.

Thesis (Ph. D.)--Oregon Graduate Center, 1986.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (p. 169-176).

The subject of this thesis is the theoretical investigation of the possibility of observing magnetic self-pinching of the hole-electron plasma present in a semiconductor. The steady-state pinch equations are derived for conditions which might be expected to prevail in such a plasma, both with and without the effects of generation and recombination. Recent reports of the observance of pinch effect in indium antimonide operated under avalanche breakdown conditions are discussed. All these reports based their claim of observing pinch on slight changes in overall resistance of the sample, a purely secondary effect of self- pinching. It is indicated that a plasma generated by avalanching is a poor medium from which to compare experimental results with available theory. Hence it is concluded that the above reports offer only circumstantial evidence of self-pinching. Finally, an experimental arrangement is suggested with which one should be able to determine unambiguously whether or not pinch can occur in semiconductors. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

In nucleonic energy determinations, pulses from capacitive sources must be amplified with the addition of a minimum amount of noise. The problems encountered in this were considered both theoretically and experimentally. The "classical" theory of Gillespie for systems using ion chambers and tube amplifiers is generalized to include systems using the modern solid-state detectors and amplifiers. Expressions are found relating the "equivalent input noise charge" to the characteristics of the detector, the preamplifier, and the pulse-shaping network. A relationship is derived between the equiv-noise charge and the conventional noise figure of an amplifier. It shows that amplifiers suitable for nucleonic work have noise figures much lower than 1 db. The theoretical study shows that conventional vacuum tubes, Nuvistors, and field effect transistors are the best active devices for this application. Junction transistors, tunnel diodes, para-metric amplifiers and Masers are shown to be unsuitable. Experimental measurements made on preamplifiers built with tubes, Nuvistors, and field effect transistors confirm the theoretical predictions with good accuracy. When the detector capacitance is 20pf, the preamplifiers exhibited noise charges of 310, 360 and 670 electronic charges respectively. The E810F tube is superior to other tubes currently used, while the field effect transistor is, at present, the best solid-state device. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Frequency converters using pumped nonlinear conductance and pumped nonlinear capacitance with the property of signal flow in one direction only are the subject of this thesis. The unilateral property can be obtained either by a suitable termination at the image frequency or by quadrature pumping the conductance and capacitance. Of great importance is a frequency converter in which the output frequency is lower than that of the input. Such a down—converter based upon a proposed image termination method is examined both analytically and experimentally. Conditions are given which the conductance and capacitance must satisfy in order that the image termination be passive. The conditions are fulfilled by a single tunnel—diode. It is found that a forward- to reverse-gain ratio of at least 20 db over a 5% bandwidth is feasible; the estimated noise figure is 3.4 db. The quadrature pumped converter is compared with the image terminated converter and it is shown in particular that the former can be unilateral only at one frequency. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Electrodeless techniques for semiconductor measurements, based on the inductive coupling of the sample to coils, are investigated in the first part of the thesis. The theory and the experimental techniques of two main experiments are developed and applied to several samples. The second part of the thesis is devoted to discussing dimorphic phase transformations in compound semiconductors. In the first experiment the sample is placed in the core of a solenoid which la excited by a sine wave generator. Eddy currents are induced in the sample and they set up a secondary magnetic field which opposes the primary field resulting in a decrease in flux through the core. The result is that a complex impedance is reflected into the coil. The increase in resistance and decrease in inductance of the coil is measured by a Q-meter technique and related to the conductivity for long cylindrical and spherical geometry samples. Design considerations are discussed, and it is shown that the optimum frequency to use, in order to obtain maximum sensitivity with the Q-meter, will depend on the conductivity of the material. Longitudinal and transverse magnatoresistance are observed by applying a static magnetic field along the appropriate axis of the solenoid. The second experiment is a crossed magnetic field determination of the Hall mobility. Circulating eddy currents are induced in the sample by a sinusoidally excited coil and a static magnetic field is applied along a second axis. The static field will rotate the plane of the eddy currents through the Hall angle, uHB, the product of the Hall mobility and the static field. The effect is the appearance of an alternating magnetic field along the third axle. This field, which at low frequencies is directly proportional to the Hall mobility, is detected by a second coil. The technique is very general and it is independent of the conductivity. In particular, it may be used to determine the Hall mobility of powders and liquids to which it is difficult or impossible to attach electrodes. In the second part of the thesis the compound semiconductor silver selenide is investigated. The sample could be obtained commercially only in powder form and hence the electrodeless techniques were essential. The temperature variation of conductivity above and below the phase transition, activation energies, relative conductivities at the phase transition and a conductivity-temperature hysteresis effect were observed. Absolute conductivity values were not obtained because of lack of knowledge of the radii of the individual powder grains and the Hall mobility measurements indicated that the sample was very impure, electronically speaking, and hence only impurity scattering was being measured. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The theory of conductivity modulation in semiconductors and the conditions under which negative resistance can be obtained are investigated. The ambipolar transport equation is derived for one-dimensional flow in a two-terminal homogeneous semiconductor with no trapping and no temperature gradients. Charge neutrality is assumed in the majority of the models studied. A phenomenological model is considered first to show how conductivity modulation can lead to negative resistance. Since the general problem of carrier transport with drift and diffusion currents is difficult, the models investigated are mainly concerned with either drift or diffusion as the dominant transport mechanism. For a unipolar space-charge limited drift model, negative resistance in frequency bands is found. For bipolar, neutral drift models, negative resistance is found under special conditions for the case of no recombination and for recombination with a carrier lifetime increasing with carrier density. For recombination with a constant lifetime, the bipolar drift model gives current-voltage characteristics of the form: J α V at low injection levels, J α V² at high injection levels, and J α V³ at very high injection levels. Space charge is important in the cube law case. Models ignoring diffusion are shown to be valid only for extrinsic semiconductors. Bipolar neutral flow with equal carrier densities leads to diffusion solutions of the ambipolar equation. This case applies to extrinsic material at high injection levels as well as to intrinsic material and is found to exhibit negative resistance under certain conditions. The most favourable situation is the case where the carrier lifetime increases with carrier density. The dependence of the lifetime with carrier density determines the possibility of defining completely a negative resistance model. It is found that the properties of the contacts are important in attaining negative resistance. Contacts and their properties are briefly discussed in relation to the carrier density boundary conditions. Avalanche injection and its relation to the conductivity modulation problem is considered. Several outstanding problems, both theoretical and experimental, arising from this thesis are outlined in the last chapter. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Metal-semiconductor contacts have been known empirically to obey a modified diode equation I = I (exp qV/akT - 1) where the parameter 'a' often took values greater than two. However, previous theories, which are briefly summarized in the thesis, could not simply account for the anomaly where 'a' is greater than two. Previous theories are extended by considering one-dimensional bipolar flow of carriers and neglecting recombination in a homogeneous semiconductor filament with a rectifying and an ohmic contact at opposite ends. The zero-electron-current theory by Borneman et. al. (1955) is extended to high injection levels by using the junction relations of Misawa (1955). Then the non-zero-electron-current theory is developed. This theory shows that 'a' is unity for low Injection Into extrinsic semiconductors and that a = (3b-M)/(b-M) for arbitrary injection into intrinsic semiconductors and, for high injection Into extrinsic semiconductors, where 'M' is the electron to hole current ratio and 'b' is the electron to hole mobility ratio. Thus, 'a' can take any value depending on the magnitude of M/b. To check the non-zero-electron-current theory, experiments were performed only on n-type germanium. Rectifying metal-semiconductor contacts were made by electroplating copper and rhodium on germanium and ohmic contacts were made by alloying antimony-doped gold wire in a nitrogen atmosphere. A side-arm probe adjacent to the plated-contact measured the voltage across the contact. For the rhodium-contact specimen, two side-arms adjacent to the rhodium contact on opposite sides of the germanium filament were used to measure the transverse a-c resistance as a function of longitudinal d-c current. This measurement demonstrated the occurrence of injection and extraction at the contact and that the level of injection was from moderate to high in the vicinity of the contact for longitudinal current density between about 10 mA/cm² and 1000 mA/cm² . Comparison of the I-V measurements of the contacts with the non-zero-electron-current theory indicated that an intermediate level of injection occurred at the rhodium contact for longitudinal current density between about 0.1 mA/cm² and 100 mA/cm² and that high injection occurred, with M = 4.94, at the copper contact for current density between about 1 mA/cm² and 50 mA/cm². Thus, the level of injection can be calculated by comparison of the experimental value of 'a' with the non-zero-electron-current theory. / Science, Faculty of / Physics and Astronomy, Department of / Graduate