The dissertation is devoted to the development of a photo-stimulated planar Hall sensor based on cadmium sulfide (CdS) with enhanced sensitivity and an extended dynamic range for magnetic-field measurement. The research addresses the relevant scientific and technical problem of the limited capability of conventional Hall sensors to provide adaptive sensitivity control, since their characteristics are mainly determined by the electrophysical properties of the material and the geometry of the active region. The proposed approach is based on using photogeneration of charge carriers as an independent control channel for adjusting sensor parameters without modifying either the sensor structure or the electronic circuitry of the measurement system. The dissertation consists of an introduction, four chapters, conclusions, a list of references. The introduction substantiates the relevance of the research topic, formulates the aim and objectives of the study, defines the object, subject, and research methods, and presents the scientific novelty and practical significance of the obtained results. The first chapter analyzes the current state of Hall sensor development, considers the main types of Hall effects, and reviews the features of macro-, micro-, nano-, and quantum devices. Existing mathematical models, materials, and Hall sensor topologies are also examined. It is shown that most contemporary methods for sensitivity enhancement are implemented during sensor fabrication and do not provide the possibility of changing sensitivity during operation. The feasibility of using photosensitive monocrystalline CdS as the material of the active region is substantiated. The second chapter presents a mathematical model of the photo-stimulated planar Hall sensor, which takes into account photogeneration of charge carriers, changes in electron and hole concentrations, their mobilities, and the effective thickness of the active region. Analytical relationships between irradiation parameters, magnetic field, and Hall voltage are obtained on the basis of conductivity, continuity, and galvanomagnetic equations. The effects of optical radiation intensity, absorption coefficient, lifetime of nonequilibrium charge carriers, and effective active-region thickness on sensor characteristics are investigated. The conditions providing the maximum increase in sensor sensitivity are determined. The third chapter presents the results of experimental studies of the developed sensor. The dependences of Hall voltage on magnetic induction under different optical irradiation conditions are investigated, amplitude-frequency and phase-frequency characteristics are obtained, and the experimental results are compared with the mathematical model. Finite-element numerical modeling of physical processes in the CdS crystal confirms the linear variation of Hall voltage within the adopted assumptions and makes it possible to determine the applicability limits of the developed model. Deviations of the experimental characteristics from the simulation results are explained by contact effects, noise, parasitic parameters, and nonlinear phenomena that are not included in the numerical model. The fourth chapter proposes a method for measuring magnetic induction using the photo-stimulated Hall sensor in large-signal and small-signal operating modes. An equivalent electrical circuit of the sensor is developed, its transfer, amplitude-frequency, and phase-frequency characteristics are investigated, and the main parameters of the measurement system are determined. The possibility of adaptive sensitivity control by varying the optical irradiation parameters is substantiated. The scientific novelty of the obtained results lies in the development of a new type of photo-stimulated planar Hall sensor in which the active region is formed under optical irradiation. The mathematical model of the sensor is improved by taking into account charge-carrier photogeneration and variation of the effective active-region thickness. Optimal irradiation parameters providing a substantial increase in sensitivity are determined, and a method for magnetic-field measurement over a wide dynamic range is developed. The practical significance of the research lies in the development of a photo-stimulated Hall sensor that provides a controlled sensitivity increase by a factor of 1.8–2.1, an increase in voltage sensitivity from 0.06±0.006 to 0.12±0.012 mV/mT, an extension of the bandwidth from 200–210 kHz to 270–280 kHz, and magnetic-induction measurement within the range of 10⁻⁵–1 T without modifying the sensor structure. The obtained results can be used in adaptive magnetometers, current sensors, position sensors, non-destructive testing systems, and other measurement systems. Four scientific publications present the main results of the dissertation, including one paper indexed in Scopus, two papers published in Ukrainian professional scientific journals of Category B, and one conference.
