Wide bandgap semiconductor visible light-emitting diodes (LED) development has spawned the prestigious Nobel Prize in Physics in 2014. Building upon this success, the scope of research has expanded to ultrawide bandgap semiconductors, which possess immense potential in the realm of deep ultraviolet (DUV) photonics. These materials have gained attention for their applicability in various areas, including public sterilization, solar-blind DUV communication, and real-time monitoring. Leveraging on the unique ultrawide tunable bandgap property, highly crystalline capability, and robust behavior, group III-Oxide and III-Nitride semiconductors were employed for sensitive DUV photodetector (PD) and efficient DUV emission, respectively. The primary research are as follows: • III-Oxide heteroepitaxial growth optimization: The influences of substrate temperature, laser energy, and oxygen pressure for the Ga2O3 growth are systematically investigated. Furthermore, the doping capability, multi-phase availability, and bandgap tunability are demonstrated. • Flexible Ga2O3 film growth and electronic devices: Flexible Mica substrate is employed to epitaxially grow κ-phase Ga2O3 thin film. The fabricated flexible PD has an Iphoton/Idark ratio of over 107 under DUV luminescence. The fatigue test performed with 1-3 cm bending radii and 10,000 bending cycles exhibits the robust flexibility of the demonstrated DUV PD. • Transferable Ga2O3 membrane for vertical electronics: Mica as a Ga2O3 growth platform enables the large-scale transfer of ultra-thin Ga2O3 membrane from mica to arbitrary tape due to the weak interfacial bond energy. A vertical and self-powered PD is demonstrated with a responsivity of 17 mA/W under DUV illumination and 0 V bias. • Interfacial mismatch engineering for freestanding Ga2O3 membrane: Looking beyond the hetero-mismatch and engineering the interfacial thermal strain between Si-doped Ga2O3 and AlN could result in the exfoliation of freestanding ultrathin Ga2O3 membrane, allowing vertical device configuration and preferable thermal management. The exfoliation mechanism has been clarified and vertical DUV PD with high on/off ratio is demonstrated. • Efficient III-Nitride LEDs: Buried polarization-induced tunneling junction is employed to suppress electron overflow and simultaneously enhance hole injection. Furthermore, monolithic integration of DUV and visible LEDs is proposed and demonstrated by deliberately cascading DUV and visible active regions, which could replace the current integration technique in the sterilization system.

At the heart of all power electronic systems lies the semiconductor, responsible for passing large amounts of current at negligible power losses in the on-state, while instantaneously switching to withstand high voltages in the off-state. For decades silicon (Si) has dominated nearly all aspects of electronic systems including power. As importunity for efficiency at higher power and fast switching speeds grows, the environments with which these systems are being tasked to operate in has also increased in rigor. This has placed semiconductors at the forefront of innovation as novel materials are being explored in hopes of meeting the demands for the future of power electronics. This exploration of novel materials for power electronics has come to fruition as the performance limits of narrow bandgap (EG) materials such as Si (1.1 eV) have been reached. The EG is a key measure of a materials ability to operate at high voltages and within high temperature environments. This is due to the direct relationship of the EG to the critical field strength which enables increased performance beyond that of narrow band gap materials such as Si and gallium arsenide. Wide bandgap (WBG) materials such as silicon carbide (SiC) and gallium nitride (GaN) with EG 3.3 eV and 3.4 eV, respectively, have emerged within the power electronics field to offer increased breakdown voltages (VBR) at lower on-resistances. However, ultrawide bandgap (UWBG) devices possess greater potential with superior performance limits in comparison to SiC and GaN. Ga2O3 (4.8 eV) is the only UWBG semiconductor with melt-growth capabilities that has already demonstrated research grade wafers up to 6" in diameter. Ga2O3 is also advantaged by the ability to grow thick, lowly-doped homoepitaxial drift regions from methods such as halide vapor phase epitaxy (HVPE) and metal organic chemical vapor deposition (MOCVD). This makes Ga2O3 a prime candidate for vertical power rectifiers as thick, high quality drift regions are a necessity for high voltage devices such as the PN diode, junction barrier Schottky (JBS) diode, merged-PiN-Schottky (MPS) diode, and Schottky barrier diode (SBD). However, Ga2O3 exhibits a lack of p-type conductive that arises from an absence of dispersion within the valence band maximum. This has caused researchers to abandon the idea of homojunction devices that Si, SiC, and GaN devices benefit from; shifting to a heterojunction approach where NiO (3.7 eV) provides the source of p-type conductivity. This complicates fabrication and device characterization particularly for the Ga2O3 JBS diode where an etched Ga2O3-NiO heterojunction has thus far been unreported throughout the literature. This work investigates the numerous individual aspects that comprise an etched Ga2O3 heterojunction device which include the etching method, post etch damage removal and its impact on electrical performance, and ohmic and Schottky contacts critical for a JBS diode; all culminating in the demonstration of a JBS and MPS diodes. We also report our investigations into co-doping of Ga2O3 that yield degenerately doped epitaxial layers with record mobility (μ) values. While not directly correlated with Ga2O3-NiO heterojunction devices, this study lays the ground work for semi-insulating Ga2O3 depletion into unintentionally doped (UID) n-type Ga2O3. / Doctor of Philosophy / Power semiconductor devices reside at the center of many critical infrastructures that power modern society. These systems include but are not limited to; telecommunications, power supplies, motor drives, and electric trains. The semiconductors embedded within these systems are tasked with passing large amounts of current at negligible power losses in the on-state, while simultaneously withstanding high voltages in the off-state. For decades, the ground breaking discoveries and engineering feats produced by scientist and engineers have propelled the field of power electronics forward. As importunity for efficiency at higher power and fast switching speeds grows, the environments with which these systems are being tasked to operate in has also increased in rigour. These demands cannot be met with traditional silicon (Si) based devices as the material properties have been pushed to their performance limits. This has led to emerging and novel wide and ultrawide bandgap semiconductors such as silicon carbide (SiC), gallium nitride (GaN), and gallium oxide (Ga2O3) becoming a greater presence within the field of high power electronics. Ga2O3 in particular has seen a recent surge in interest within the power electronics communities due to the prospect of meeting the aforementioned demands, aided by a number of advantageous material and electrical properties. Ga2O3 is unlike any other wide or ultrawide bandgap material in that high quality Ga2O3 films known as epitaxial layers can be deposited atop native meltgrown Ga2O3 substrates. This reduces any mismatch or undesirable boundaries between the substrate and epitaxial layers that could otherwise impact device performance. This makes Ga2O3 a prime candidate for vertical power rectifiers, or switches such as a PN diode, junction barrier Schottky (JBS) diode or Schottky barrier diode (SBD). However, there has been no realization of p-type conductivity, or positively charged mobile carriers, within Ga2O3. This makes devices such as the PN and JBS diode difficult, as they rely on both n- and p-type conductivity. Without a source of p-type conductivity, Ga2O3 will be limited to unipolar devices that lack superior breakdown voltages and robustness. This work explores Ga2O3 heterojunction diodes, specifically the JBS diode, where nickel oxide (NiO) is used as the source of p-type conductivity. The need for a heterojunction introduces a host of issues that are otherwise not seen within bipolar semiconductors such as Si, SiC, and GaN. Our work details the analysis of the individual aspects that comprise a Ga2O3 heterojunction barrier Schottky diode including the etching process, etch damage removal, NiO sputtering, and contact formation. Our efforts have provided insight into unexplored areas within the Ga2O3 literature, leading to the first demonstration of a Ga2O3 merged- PiN-Schottky (MPS) diode; a more robust JBS diode capable of handling surge current. This work serves to further Ga2O3 as a viable semiconductor for the future of high power vertical rectifiers.

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<p>As the interest in intentional electromagnetic interference (IEMI) increases, so does the need of a suitable antenna which endures those demanding conditions. The ultrawideband (UWB) technology provides an elegant way of generating high-voltage UWB pulses which can be used for IEMI. One UWB antenna, invented solely for the purpose of radiating pulses, is the impulse radiating antenna (IRA). In the course of this master thesis work, a suitable geometry of the IRA is suggested, and modelled, for the high-voltage application of 90 kV.</p>

Modern wireless communication systems call for ultra wideband operations to meet the continuous growth in the number of users of these systems. Since antenna is an integral part of any wireless communication system (transmitter or receiver), designing antennas with good gain over large bandwidth needs to be considered first. To meet the popular demand, wireless communication systems should be as cheap as possible which require antennas with small size, light weight, low profile and low cost, and that are easy to fabricate and assemble. A type of antenna that satisfies most of these requirements is the microstrip antenna. Most of the wideband techniques for microstrip antennas utilize complicated geometries such as stacked multiple metal/dielectric layers, complicated feed arrangements etc., which elude the primary attraction of microstrip antennas. On the other hand, single layer suspended configurations are considered the best choice as these are simple to fabricate and assemble. The objective of this research is to investigate simple microstrip antennas with large bandwidth. A single layer suspended microstrip configuration was chosen for the purpose. In the first part of the research, the bandwidth was increased to about 50% with linear phase characteristics by optimizing the feed configurations while retaining the overall simplicity. This study has resulted in proposing a criterion for obtaining maximum bandwidth in the suspended microstrip configuration. An analytical model has been developed for such an antenna configuration. Although several analytical tools are available for the microstrip antenna analysis, equivalent circuit based approach proves to be a simple one and offers convincingly accurate results. Another advantage of the proposed equivalent circuit modeling scheme is that it is suitable for computer aided design (CAD). In order to make this approach even more useful, the antenna designed in the first part was modified to meet desired specifications such as reduction in the air gap to make the antenna compact, symmetrical patterns, making antenna circularly polarized (LHCP or RHCP) without changing the feed configuration. Nearly symmetrical patterns were obtained throughout the band of operation by modifying the profile of patch close to the feed strip. Circular polarization (CP) operation has been obtained from the basic antenna by cutting a diagonal slot on the radiator patch. Here the slot orientation decides the type of CP i.e., LHCP or RHCP. In this work obtained of 7.1% axial ratio (3dB) bandwidth with other characteristics unaffected. The overall height of the antenna is reduced by 55% by cutting a slot and re-optimizing the feed strip dimensions. These studies emphasize flexibility offered by the design approach in realizing practical antennas for various applications.

As the interest in intentional electromagnetic interference (IEMI) increases, so does the need of a suitable antenna which endures those demanding conditions. The ultrawideband (UWB) technology provides an elegant way of generating high-voltage UWB pulses which can be used for IEMI. One UWB antenna, invented solely for the purpose of radiating pulses, is the impulse radiating antenna (IRA). In the course of this master thesis work, a suitable geometry of the IRA is suggested, and modelled, for the high-voltage application of 90 kV.

No description available.

Emerging Ultra Wideband (UWB) Orthogonal Frequency Division Multiplexing (OFDM) systems hold the promise of delivering wireless data at high speeds, exceeding hundreds of megabits per second over typical distances of 10 meters or less. The purpose of this Thesis is to estimate the timing accuracies required with such systems in order to achieve Bit Error Rates (BER) of the order of magnitude of 10-12 and thereby avoid overloading the correction of irreducible errors due to misaligned timing errors to a small absolute number of bits in error in real-time relative to a data rate of hundreds of megabits per second. Our research approach involves managing bit error rates through identifying maximum timing synchronization errors. Thus, it became our research goal to determine the timing accuracies required to avoid operation of communication systems within the asymptotic region of BER flaring at low BERs in the resultant BER curves. We propose pushing physical layer bit error rates to below 10-12 before using forward error correction (FEC) codes. This way, the maximum reserve is maintained for the FEC hardware to correct for burst as well as recurring bit errors due to corrupt bits caused by other than timing synchronization errors.

This dissertation applies theories and concepts of wireless communications and signal processing to the security domain to assess the security of a Wireless secret Key Generation (WKG) system against capable eavesdroppers, who employ all the feasible tools to compromise the system’s security. The security of WKG is evaluated via real wireless measurements, where adversary knows and applies appropriate signal processing tools in ordere to predict the generated key with the communicating pair. It is shown that in a broadband stationary wireless communication channel, (e.g. commercial off-the-shelf 802.11 WLAN devices), a capable eavesdropper can recover a large portion of the secret key bits. However, in an Ultra-wideband (UWB) communication, at the same stationary environment, secret key rates of 128 bits per channel probe are achievable. / Graduate