<p>This work describes a theoretical and experimental investigation into the electrical properties and possible device applications of the three layer Metal-Insulator-Semiconductor (MIS) structure when the insulating layer is very thin (<60A). Under these conditions, current can flow between the metal and the semiconductor by quantum mechanical tunneling processes. This work is limited to the case where the semiconductor is not degenerately doped.</p> <p>To aid in the discussion of the properties of this structure, its electrical behaviour is simulated by describing the transport processes through the semiconductor and the insulator regions mathematically and solving the resulting system of mathematical equation numerically. Solutions for both the AC and DC properties of the structure are obtained in this way. Using these solutions as a guideline, a general theoretical framework is established which allows the device properties to be predicted when parameters such as the work function of the metal contact, the insulator thickness, the properties of surface states at the insulator-semiconductor (IS) interface, the device temperature, and the dopant type in the semiconductor are varied. Particular importance is placed upon the charge conditions in the semiconductor at the IS interface under zero bias conditions. Depending upon whether this region is strongly inverted, depleted, or accumulated, the dominant component of the diode current tends to flow between the metal and the minority carrier energy band, surface state levels, and the majority carrier energy band in the semiconductor respectively. Correspondingly, the devices are classified as minority carrier, surface state, and majority carrier diodes. In addition to this classification, a distinction between "equilibrium" and "non-equilibrium" devices is made. In the former, the insulator layer is thick and the device currents small while in the latter, this layer is thinner and the enhanced current flows cause the semiconductor to depart significantly from thermal equilibrium. Experimental measurements upon the metal-silicon dioxide-silicon system are used to demonstrate the validity of this theory and also demonstrate the utility of the classification scheme described.</p> <p>Non-equilibrium diodes are of particular interest because of their possible device applications. Majority carrier non-equilibrium devices exhibit current multiplication properties which are discussed theoretically and measured experimentally. These make the devices of interest in transistor structures and in such applications as photo-diodes with internal multiplication properties. Minority carrier non-equilibrium devices are shown both theoretically and experimentally to possess properties similar to p-n junction diodes under reverse and small to moderate forward bias. Since they are considerably simpler to fabricate, they have possible application as replacing junction devices in a number of applications such as those as injecting contacts, photo-diodes, or members of photo-diode arrays. One particularly promising application is to direct energy conversion using the electron-or photo-voltaic effect. For an energy conversion situation using the radioisotope Pm147 as the primary energy source it is demonstrated that the predicted higher conversion efficiency of the MIS tunnel diode compared to the p-n junction diode can be experimentally realized.</p> / Doctor of Philosophy (PhD)

<p>The radiation damage and electrical properties of nitrogen implanted silicon, germanium and silicon cardine have been investigated. The object of this investigation has been to relate the damage annealing properties of the implanted semiconductor to the observed electrical behaviour, in an attempt to understand the role of nitrogen in these materials.</p> <p>The study has shown that donor behaviour can be obtained in nitrogen implanted silicon. Capacitance-voltage and Hall effect measurements performed on the implanted layer have indicated that less than 1% of the implanted nitrogen has become electrically active, following anneals in the 700-900ºC range. The ionization energy of nitrogen in silicon has been found by low temperature Hall measurements to be 0.017 ± 0.002 eV. This result has been shown to be independent of the annealing time and the implantation temperature. For doses above ~6 x 10¹4 N/cm², donor results are no longer observed and the damage results have shown that the silicon crystal has no recrystallized well. The results of the above measurements, together with the characteristics of nitrogen implanted diodes and the results of a damage study of nitrogen implanted silicon are presented, and the role of nitrogen in silicon is discussed.</p> <p>The results of electrical and lattice location measurements on nitrogen implanted germanium have shown that nitrogen does not become a donor in germanium. The lattice location measurements have used the 14N(d,α)¹²C nuclear reaction, and have shown that the implanted nitrogen atoms are on interstitial lattice positions. The results of damage measurements obtained by backscattering techniques, together with the electrical and lattice location results are presented.</p> <p>This study has shown that nitrogen implanted silicon carbide exhibits donor behaviour following a high temperature anneal. This result was deduced from the properties of nitrogen implanted silicon carbide diodes and from lattice location measurements performed with the 15N(p,α)¹²C nuclear reaction. These lattice location measurements have shown that approximately 50% of the implanted nitrogen atoms are on the substitutional lattice sites, following an anneal at 1450ºC. This is in excellent agreement with the value of 50% previously reported by other authors as deduced from electrical measurements. Although some problems with the annealing of heavily doped silicon carbide remain to be solved, this study has shown that ion implantation promises to be a useful technique for doping this material.</p> / Doctor of Philosophy (PhD)

<p>The purpose of this thesis is to present a unified treatment of numerical solutions to the elliptic partial differential equations, particularly the Laplace, Poisson, and Helmholtz equations, in homogeneous and inhomogeneous isotropic media in electrostatic, magnetostatic, and electromagnetic field problems, with particular attention given to iterative solutions. Another objective is to design a family of methods for accelerating the convergence of these solutions. The concept of the convergence acceleration is generalized to deterministic and stochastic vector sequences. Several hybrid methods, combining the finite difference and finite element approaches, are proposed. The methods have been tested either by test examples or by practical solutions to field problems.</p> / Doctor of Philosophy (PhD)

<p>Pulse-compression is a technique used in radar to transmit a long pulse while retaining the range resolution of a short pulse. The echo from the target is compressed in the matched filter of the radar receiver and the range resolution becomes equal to the width of the central peak of the autocorrelation function of the transmitted signal. A range tracking loop and a range surveillance moving target indicator (MTI) radar using pulse-compression techniques are studied in this thesis. The antenna of these systems is assumed to point along a constant azimuth to simplify the radar surroundings so that the nonlinear aspects of the circuits may be investigated.</p> <p>In a range tracking loop the nonlinearity arises in the delay error feedback process, while in an MTI radar it arises through the limited dynamic range of the circuits used. This thesis presents a computer simulation study of these nonlinear radar systems using Monte Carlo techniques. The computer used in the study is of an interactive kind with oscilloscope display.</p> <p>A new range tracking loop referred to as the decision-directed delay-lock loop has been developed using the fast Fourier transform (FFT) for cross-correlation with a stored replica of the transmitted signal. The loop uses all the lagged products of the FFT cross-correlation output, ans is shown to have a wide dynamic range for large steps of input delay. Using signals already available in the loop, additional features such as automatic feedback gain control and a mechanism for detection of unlocking are built into the loop.</p> <p>The MTI pulse-compression radar has been investigated to determined the effect of a linear-limiting intermediate frequency (IF) amplifier on the signal-to-noise ratio (SNR) at the MTI output. For this study the FFT was used for the purpose of matched filtering and for generating various types of coherent clutter. It has been shown that large SNR losses due to the time-varying effective gain of the clutter-captured limiter may occur at some ranges with particular types of clutter spatial distributions.</p> / Doctor of Philosophy (PhD)

<p>This thesis is concerned with investigating the production of thin film Bi-Sb alloys by ion beam mixing. Samples were composed of a thin Sb film sandwiched between two Bi layers; the thicknesses of the films were varied to produce composition range from 0 to ~45% Sb. The overall thickness was about 55 nm.</p> <p>Analysis of the films by Rutherford Backscattering Spectrometry (RBS) and Auger Electron Spectroscopy (AES) indicated that ion beam mixing can produce uniform Bi-Sb alloys with doses of about 2.8X10¹⁵ cmˉ² of 80 KeV Ar⁺ at room temperature. The results of Electron Microscopy showed a grain growth due to ion bombardment.</p> <p>The mixing was characterized by the increase in the full width at half maximum (FWHM) of the Sb signal in the RBS spectra. It was measured as a function of ion dose, dose rate, mass, and energy. The dependence of mixing on the temperature was also investigated. A square-root dependence of mixing on the dose confirmed a diffusion like mixing process. The rate of mixing per ion dose was found to increase with the elastic energy deposited at the Bi/Sb interface. The mixing is temperature independent in the range of ~40 to ~266 K, i.e., collision cascade mixing dominates. An effective diffusion coefficient, D*, of about 4.9X10ˉ²⁸cm⁴/ion was determined. At temperatures higher than ~266 K, the mixing increases with the temperature. This suggests that a radiation enhanced diffusion mechanism is the dominant mixing process. An effective diffusion coefficient of ~1.7X10ˉ²⁷cm⁴/ion at room temperature was calculated: an activation energy of ~0.15 eV was found.</p> <p>Thermoelectric characteristics of the alloys were investigated by measuring the thermal voltage, V₃, as a function of the temperature, T, in the range 300-500 K, for alloys with various composition. The thermal voltage was found to have a linear dependence on temperature. The thermoelectric power, dV₃/dT, reaches a maximum of about 70 μV/deg, for Bi₈₇Sb₁₃. The dependence of the thermoelectric power on Sb concentration agrees with the model put forward to explain the transport properties of bulk Bi-Sb alloys. An empirical model has been proposed to relate the state of mixing with the measured thermoelectric power.</p> / Doctor of Philosophy (PhD)

<p>This thesis examines receiver structures based on maximum likelihood sequence estimation (MLSE) for receiving quaternary phase-shift-keyed (QPSK) signals over bandlimited, non-linear satellite channels, in the presence of additive down link gaussian noise. Two satellite channel models are considered. In the first channel model, the effects of intersymbol interference caused by filtering followed by AM/AM and AM/PM conversions are taken into account while the second channel model includes a post-nonlinearity filter.</p> <p>An explicit expression for the output of the bandpass nonlinearity (BPNL) for a QPSK signal is obtained in terms of an inphase (1)-quadrature (Q) path memory parameter Pk. The computation of the output of the BPNL requires a knowledge of its transfer characteristic. The transfer characteristics may be specified either analytically or through experimental measurements.</p> <p>An optimum MLSE receiver structure for bandlimited, non-linear satellite channel is derived and its performance evaluated using computer simulation. Simulating the MLSE receiver in optimum form is too time consuming, so we estimated the I-Q path history parameter pk'S by using a simple procedure analogous to decision feedback processing. Although this method is not theoretically equivalent to an optimum computation, our results show that it performs essentially as well as an optimum computation. For moderate to high SNR, an upperbound on the probability of symbol error is obtained, using the concept of error events. A simplified expression for an upperbound on probability of symbol error, for the case when single-error error events are dominant is also obtained. A sub-optimum receiver structure is then derived using average matched filter responses. The sub-optimum receiver which turns out to be a complex filter followed by a decision device, is a relatively simple structure. The performance of the sub-optimum receiver was estimated for two different uplink filters. The effect of varying the BPNL input drive level was also studied. Our simulation results indicate that the performance of both the MLSE and the sub-optimum receivers approach asymptotically the same optimum performance band.</p> <p>Finally, we extend our results on an optimum receiver structure for receiving QPSK signals over a digital satellite communications channel, to include the effects of filtering following the non-linear satellite transponder. It is shown that the complexity of the MLSE receiver is primarily determined by the uplink channel memory. The error performance of the receiver at low signal-to-noise ratios is evaluated by computer simulation. An upperbound on the probability of symbol error at moderate to high SNR is also obtained. A sub-optimum receiver similar to the uplink channel filtering case is developed and its performance evaluated using computer simulation. The degradation in performance of the sub-optimum receiver compared to the optimum receiver is found to be small.</p> / Doctor of Philosophy (PhD)

<p>This thesis addresses itself to the computer-aided design and modelling of microwave circuits using efficient minimax and ℓ₁ optimization techniques.</p> <p>Recent algorithms for nonlinear minimax and ℓ₁ for the particular applications of this thesis. Efficient gradient approximation techniques applicable to both minimax and ℓ₁ optimization are presented.</p> <p>A comparative example with ℓ₂ optimization illustrates the robustness of ℓ₁ for the particular applications of this thesis. Efficient gradient approximation techniques applicable to both minimax and ℓ₁ optimization are presented.</p> <p>A simplified and straightforward treatment of sensitivities for two port networks, cascaded and branched cascaded structures is introduced. The objective is to calculate the sensitivities efficiently, without appealing to the adjoint network concept. A novel proof of a recent result in sensitivity analysis of lossless and reciprocal two-ports is presented.</p> <p>Design of manifold type waveguide multiplexers has been considered as a major application for both minimax optimization and the theoretical work in branched cascaded network sensitivity analysis. Components of the multiplexer structure and nonideal effects such as dissipation and dispersion are discussed and a step-by-step implementation of an algorithm to calculate particular responses and sensitivities is presented. Examples of the design of 3-, 12- and 16-channel, 12 GHz multiplexers illustrate the practicality of the approach presented.</p> <p>A new approach to modelling of microwave devices which exploits the theoretical properties of the ℓ₁ norm is presented. The concept of multi-circuit measurements is introduced and its merits in obtaining unique and self-consistent parameters are discussed. The technique is applied to modelling of multi-coupled cavity filters and GaAs FET's. The application of efficient modelling techniques in developing algorithms for postproduction tuning and in establishing the relationship between physical parameters of a device and its equivalent circuit model parameters is discussed.</p> / Doctor of Philosophy (PhD)

<p>This thesis concerns itself with computer-aided techniques for design centering, tolerancing and tuning, fault location and model parameter identification from measurements.</p> <p>Since many of the engineering system problems discussed in this thesis are formulated as optimization problems we examine algorithms and techniques for nonlinear optimization. Our attention is focused on minimax and ℓ₁ algorithms since many formulations of engineering system problems exploit the characteristic features of these two norms.</p> <p>A novel approach for worst-case network design is proposed and an algorithm for the fixed tolerance problem embodying worst-case search and selection of sample points is presented.</p> <p>The features of the ℓ₁ norm in the tuning problem are discussed in detail and explained using necessary conditions for optimality of the nonlinear ℓ₁ problems with nonlinear constraints. Regular and singular ℓ₁ problems are defined and a criterion for determining a singularity present in the ℓ₁ problem is formulated.</p> <p>New formulations using the ℓ₁ norm are given for fault isolation and model parameter identification in analog circuits.</p> <p>Practical engineering problems have been solved illustrating the wide applicability of the concepts used and the robustness of the algorithms employed.</p> <p>A new algorithm for minimizing the cardinality of a set subject to nonlinear, nondifferentiable constraints is presented and illustrated by solving the best mechanical alignment problem. The load shedding and generation rescheduling problem in power systems is formulated using the ℓ₁ norm. The formulation is tested on 6-bus and 26-bus power systems. A general microwave multiplexer design procedure exploiting exact network sensitivities is introduced and illustrated by designing 5-channel, 11 GHz and 12-channel, 12 GHz multiplexers.</p> / Doctor of Philosophy (PhD)

<p>A new adaptive procedure for the detection of a random signal in a background of colored interference plus white noise, all having unknown statistics is derived. The procedure is based on the development of linear models for the two hypotheses H₀ and H₁. Under hypothesis H₀ a wanted signal is absent and under H₁ the wanted signal to present. After parameterizing the input signal under the two hypotheses, the log likelihood ratio is easily established in terms of the innovations processes. The test statistic thus obtained has an intuitive interpretation, which conversely provides a basis for the choice of model candidates for the signal detection problem. Different modelling approaches generally result in different receiver performance. Therefore, choosing appropriate type of model for the two pypotheses is a key step in order to enhance detection. A computationally efficient technique has been developed for this purpose.</p> <p>This adaptive detection method is applied to construct a radar detection scheme for detecting a moving target in a surveillance radar environment. The detector is composed of a pair of adaptive whitening filters followed by a log likelihood ratio calculator. The new scheme is tested by using actual radar data, including weather and ground clutter. Comparison is made with the previously described scheme known as innovations-based detection algorithm (IBDA). The results show that the performance of the new scheme is much better than the IBDA.</p> <p>In a related study, the spatial correlation between radar clutter from adjacent rings is exploited to construct two new adaptive clutter suppression schemes. The schemes are tested by real radar data. Experimental results show that these schemes are around 5 dB and 10 dB better than the adaptive lattice prediction-error filter in terms of improvement factor, respectively.</p> / Doctor of Philosophy (PhD)

<p>The problem of identification (estimation of system parameters and characteristics) is considered. The aspect emphasized is the robustness in identification. By saying robustness, two points are meant. One is the robustness with respect to bad pieces of data and the other is the numerical robustness with respect to truncation and round-off errors in computation.</p> <p>A thorough study has been made on the robust statistical principles and their applicability in system identification is critically evaluated. Off-line and on-line identification algorithms are proposed, which are resilient to undetectable spurious errors in the data and at the same time computationally simple and efficient. The convergence of these algorithms is theoretically established. Besides, a robust recursive algorithms is also proposed which jointly estimates the states and parameters of a linear system in a bootstrap manner. This algorithm is also proven to be converging with probability one. In addition to this, a very general method is developed for evaluating the asymptotic efficiency of robust identification methods. The superiority of the proposed approaches in contrast with the conventional identification methods (least squares and its genaralizations) is illustrated with the help of several simulated as well as real-life examples.</p> <p>The numerical instability caused by improper choice of sampling rates is also subjected to considerable study in the context of identification of continuous-time systems from samples of input-output data. Methods are suggested to overcome this problem. Also, numerically robust schemes are introduced for transforming discrete-time models to their continuous-time equivalents and their performance is compared with other existing methods.</p> / Doctor of Philosophy (PhD)