As a power device material, SiC has gained remarkable attention to its high thermal conductivity and high breakdown electric field. SiC bipolar junction transistors (BJTs) are interesting for applications as power switch for 600 V-1200 V applications. The SiC BJT has potential for very low specific on-resistances and this together with high temperature operation makes it very suitable for applications with high power densities. One disadvantage of the BJT compared with MOSFETs and Insulated Gate Bipolar Transistors (IGBTs) is that the BJT requires a more complex drive circuit with higher power capability. For the SiC BJT to become competitive with field effect transistors, it is important to achieve high current gains to reduce the power required by the drive circuit. Although much progress in SiC BJTs has been made, SiC BJTs still have low common emitter current gain typically in the range 10-50. In this work, a record high current gain exceeding 60 has been demonstrated for a SiC BJT with a breakdown voltage of 1100 V. This result is attributed to an optimized device design, a stable device process and state-of-the-art epitaxial base and emitter layers. A new technique to fabricate the extrinsic base using epitaxial regrowth of the extrinsic base layer was proposed. This technique allows fabrication of the highly doped region of the extrinsic base a few hundred nanometers from the intrinsic region. An important factor that made removal of the regrowth difficult was that epitaxial growth of very highly doped layers has a faster lateral than vertical growth rate and the thickness of the p+ layer therefore has a maximum close to the base-emitter sidewall. A remaining p+ regrowth spacer at the edge of the base-emitter junction is proposed to explain the low current gain. Under high power operation, the SiC BJTs were strongly influenced by self-heating, which significantly limits the performance of device. The DC I-V characteristics of 4H-SiC BJTs have also been studied in the temperature range 25 °C to 300 °C. The DC current gain at 300 °C decreased 56 % compared to its value at 25 °C. Selfheating effects were quantified by extracting the junction temperature from DC measurements. To form good ohmic contacts to both n-type and p-type SiC using the same metal is one important challenge for simplifying SiC Bipolar Junction Transistor (BJT) fabrication. Ohmic contact formation in the SiC BJT process was investigated using sputter deposition of titanium tungsten to both n-type and p-type followed by annealing at 950 oC. The contacts were characterized with linear transmission line method (LTLM) structures. The n+ emitter structure and the p+ base structure contact resistivity after 30 min annealing was 1.4 x 10-4 Ωcm2 and 3.7 x 10-4 Ωcm2, respectively. Results from high-resolution transmission electron microscopy (HRTEM), suggest that diffusion of Si and C atoms into the TiW layer and a reaction at the interface forming (Ti,W)C1-x are key factors for formation of ohmic contacts. / QC 20101208

A novel strategy for the intercalation of antimony (Sb) under the (6√3 × 6√3)R30° reconstruction, also known as buffer layer, on SiC(0001) is reported. Using X-ray photoelectron spectroscopy, low-energy electron diffraction, and angle-resolved photoelectron spectroscopy, it is demonstrated that, while the intercalation of the volatile Sb is not possible by annealing the Sb-coated buffer layer in ultrahigh vacuum, it can be achieved by annealing the sample in an atmosphere of Ar, which suppresses Sb desorption. The intercalation leads to a decoupling of the buffer layer from the SiC(0001) surface and the formation of quasi-freestanding graphene. The intercalation process paves the way for future studies of the formation of quasi-freestanding graphene by intercalation of high-vapor-pressure elements, which are not accessible by previously known intercalation techniques, and thus provides new avenues for the manipulation of epitaxial graphene on SiC.

Stand der Technik sind IGBTs und Freilaufdioden aus Silizium (Si). Jahrzehntelange Forschung hat zu einer nahezu perfekten Technologie geführt. Jedoch werden die Fortschritte hinsichtlich der Reduzierung von Schalt- und Durchlassverlusten mit jeder neuen Generation von Si-IGBTs immer kleiner. Die anfallende Verlustleistung kann jedoch signifikant mit Leistungshalbleiter-Bauelementen aus Siliziumkarbid (SiC) und Galliumnitrid (GaN) gesenkt werden. Ziel dieser Arbeit ist es, zu untersuchen, ob und inwieweit mit diskreten SiC-Bipolartransistoren im TO-247- und SiC-Schottky-Dioden im TO-220-Gehäuse der Wirkungsgrad eines Antriebsstromrichters gesteigert werden kann. Ein Exkurs in die Siliziumkarbid-Halbleitertechnologie am Anfang soll deren Vorteile in Hinblick auf verlustärmere Leistungselektronik aufzeigen. Die Vorteile des Halbleitermaterials Siliziumkarbid werden anhand des SiC-Bipolartransistors im Vergleich zum ersten Leistungstransistor - dem Bipolartransistor aus Silizium - herausgearbeitet. Beim SiC-Bipolartransistor muss im laststromführenden Zustand ein Steuerstrom in die Basis eingeprägt werden. Damit erhöht sich der Treiberaufwand. Deshalb wird der erste Themenschwerpunkt auf den Treiber gelegt. In dieser Arbeit wurden ein einfacher und ein komplexer Treiber aufgebaut und evaluiert. Mit leichten Modifikationen wurden mit dem komplexeren Treiber auch IGBTs und SiC-MOSFETs für Vergleichsmessungen angesteuert. Ein neuer Ansatz zur Reduzierung der Treiberverlustleistung im Wechselrichter mit SiC-Bipolar-Transistoren wird vorgestellt. Er setzt beim Kommutierungsalgorithmus des Wechselrichters an. Ein wesentlicher Teil der Arbeit widmet sich der Charakterisierung des SiC-Bipolartransistors, insbesondere dem Schaltverhalten. Ein- und Ausschaltwärmen für verschiedene Arbeitspunkte werden ermittelt. Am Ende der Arbeit werden experimentelle Untersuchungen an einem SiC-Wechselrichter durchgeführt. Abschließend werden die Potenziale, die mit dem Einsatz von SiC-Bipolartransistoren verbunden sind, bewertet aber auch die Grenzen aufgezeigt.:1 Einleitung 1 2 Aufbau des SiC-Bipolartransistors 2.1 Siliziumkarbid (SiC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1.1 Eigenschaften von monokristallinem Siliziumkarbid . . . . . . . . . . 5 2.1.2 Herstellung des SiC-Wafers . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1.3 Herstellung des SiC-Bipolartransistors . . . . . . . . . . . . . . . . . . 10 2.1.4 Defekte im Siliziumkarbidkristall . . . . . . . . . . . . . . . . . . . . 11 2.2 Halbleiterphysikalische Grundlagen . . . . . . . . . . . . . . . . . . . . . . . 12 2.2.1 Gesperrter pn-Übergang . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.2.2 Stromführender pn-Übergang . . . . . . . . . . . . . . . . . . . . . . . 15 2.3 Bipolartransistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.3.1 Aufbau und Funktionsprinzip . . . . . . . . . . . . . . . . . . . . . . . 17 2.3.2 Sperrfähigkeit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.3.3 Erster und zweiter Durchbruch . . . . . . . . . . . . . . . . . . . . . . 23 2.3.4 Stromverstärkung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.3.5 Ladungsträgermodulation . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.3.6 Eindimensionaler spezifischer Widerstand der Driftzone . . . . . . . . 30 3 Ansteuerung des SiC-Bipolartransistors 3.1 Einführung Treiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 3.2 Herausforderungen beim Ansteuern von SiC-Bipolartransistoren . . . . . . . . 34 3.3 Treiberkonzepte für SiC-Bipolartransistoren . . . . . . . . . . . . . . . . . . . 36 3.4 Konventioneller Treiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3.5 3-Level-Treiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.6 Treiber für SiC-MOSFET und IGBT . . . . . . . . . . . . . . . . . . . . . . . 45 4 Reduzierung der Treiberverluste durch Einschrittkommutierung 4.1 Einschrittkommutierung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 4.2 Stromvorzeichenerkennung . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 4.3 Berechnung der Verlustleistungen für den eingeschalteten Zustand des SiC- Bipolartransistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 4.4 Messung der Treiberverlustleistung . . . . . . . . . . . . . . . . . . . . . . . . 52 5 Charakterisierung des SiC-Bipolartransistors 5.1 Messaufbau für Untersuchung des Ein- und Ausschaltverhaltens . . . . . . . . 55 5.2 Doppelpulsverfahren . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 5.3 Definition der Schaltzeiten und Schaltverlustleistung . . . . . . . . . . . . . . 57 5.4 Messung der Schaltwärme . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 5.4.1 Spannungstastköpfe . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 5.4.2 Stromsensoren . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 5.4.3 Zeitliche Verschiebung der Messsignale . . . . . . . . . . . . . . . . . 62 5.4.4 Vergleich von konventionellem und 3-Level-Treiber . . . . . . . . . . . 65 5.4.5 Vergleich bei unterschiedlicher Treiberspannung . . . . . . . . . . . . 66 5.4.6 Vergleich bei halb und voll bestückter Halbbrücke . . . . . . . . . . . . 68 5.4.7 Vergleich von SiC-Bipolartransistor mit SiC-MOSFET und Si-IGBT . . 69 5.4.8 Reduzierung der Spannungsspitze beim Ausschalten . . . . . . . . . . 74 5.5 Simulation des Schaltverhaltens eines SiC-Bipolartransistors . . . . . . . . . . 79 5.5.1 Schaltverhalten bei Ansteuerung mit unipolarem Treiber . . . . . . . . 79 5.5.2 Simulation des Einfluss der Emitter-Induktivität auf Schaltwärme . . . 81 5.5.3 Vergleich von Simulation und Messung . . . . . . . . . . . . . . . . . 82 5.6 Durchlassverlustleistung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 6 Einsatz von SiC-Bipolartransistoren im Wechselrichter 6.1 Aufbau der Wechselrichter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 6.2 Inbetriebnahme des Wechselrichters . . . . . . . . . . . . . . . . . . . . . . . 89 6.3 Überspannungen an den Motorklemmen der 1 kW-Asynchronmaschine . . . . 91 6.4 Umbau des SiC-Wechselrichters . . . . . . . . . . . . . . . . . . . . . . . . . 93 6.5 Spannungsspitzen in der Ansteuerspannung . . . . . . . . . . . . . . . . . . . 94 6.6 Halbbrückenverluste im Leerlauf . . . . . . . . . . . . . . . . . . . . . . . . . 98 7 Zusammenfassung und Fazit 101 Literaturverzeichnis 104 A Anhang A.1 Netzliste für SiC-Bipolartransistor FSICBH057A120 . . . . . . . . . . . . . . 113 A.2 Leiterplatten für Doppelpuls-Test und SiC-Wechselrichter . . . . . . . . . . . . 114 A.3 Herleitung des Feldverlaufs in der Driftzone des gesperrten pn-Übergangs . . . 116 A.4 Herleitung des Emitterwirkungsgrads . . . . . . . . . . . . . . . . . . . . . . . 119 A.5 Herleitung des spezifischen Widerstands der Driftzone . . . . . . . . . . . . . 121 A.6 Lebenslauf von Henry Barth . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 A.6.1 Persönliche Angaben . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 A.6.2 Wissenschaftlicher Werdegang . . . . . . . . . . . . . . . . . . . . . . 124 / State-of-the-art are IGBTs and free-wheeling diodes made of silicon (Si). Decades of research have led to an almost perfect technology. Nevertheless, progress in terms of reduction of switching and forward conducting losses becomes smaller and smaller with each new generation of Si IGBTs. The resulting power dissipation, however, can be significantly reduced with power semiconductor devices made of silicon carbide (SiC) and gallium nitride (GaN). The objective of this work is to investigate whether and to what extent discrete SiC bipolar junction transistors (BJT) in TO-247 and SiC Schottky diodes in TO-220 packages can be used to increase the efficiency of a power drive inverter. At the beginning, a digression into silicon carbide semiconductor technology is intended to show its advantages in terms of lower-loss power electronics. The advantages of the semiconductor material silicon carbide are illustrated by the SiC bipolar junction transistor in comparison with the first power transistor - the silicon bipolar junction transistor. For the on-state of SiC bipolar junction transistors, a continuous current must be injected into the base. This increases the driving effort. Therefore, the first topic focuses on the driver. In this work, a simple and a complex driver were built and evaluated. With slight modifications, the more complex driver was also used to drive IGBTs and SiC-MOSFETs for comparative measurements. A new approach to reduce driver power dissipation in the inverter when using SiC bipolar junction transistors is presented. It focuses on the commutation algorithm of the inverter. A significant part of the work is devoted to the characterization of the SiC bipolar junction transistor, especially the switching behavior. Turn-on and turn-off switching losses for different operating points are determined. At the end of the work, experimental investigations are performed on a SiC inverter. Finally, the potentials associated with the use of SiC bipolar junction transistors are evaluated but also the limitations are shown.:1 Einleitung 1 2 Aufbau des SiC-Bipolartransistors 2.1 Siliziumkarbid (SiC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1.1 Eigenschaften von monokristallinem Siliziumkarbid . . . . . . . . . . 5 2.1.2 Herstellung des SiC-Wafers . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1.3 Herstellung des SiC-Bipolartransistors . . . . . . . . . . . . . . . . . . 10 2.1.4 Defekte im Siliziumkarbidkristall . . . . . . . . . . . . . . . . . . . . 11 2.2 Halbleiterphysikalische Grundlagen . . . . . . . . . . . . . . . . . . . . . . . 12 2.2.1 Gesperrter pn-Übergang . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.2.2 Stromführender pn-Übergang . . . . . . . . . . . . . . . . . . . . . . . 15 2.3 Bipolartransistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.3.1 Aufbau und Funktionsprinzip . . . . . . . . . . . . . . . . . . . . . . . 17 2.3.2 Sperrfähigkeit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.3.3 Erster und zweiter Durchbruch . . . . . . . . . . . . . . . . . . . . . . 23 2.3.4 Stromverstärkung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.3.5 Ladungsträgermodulation . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.3.6 Eindimensionaler spezifischer Widerstand der Driftzone . . . . . . . . 30 3 Ansteuerung des SiC-Bipolartransistors 3.1 Einführung Treiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 3.2 Herausforderungen beim Ansteuern von SiC-Bipolartransistoren . . . . . . . . 34 3.3 Treiberkonzepte für SiC-Bipolartransistoren . . . . . . . . . . . . . . . . . . . 36 3.4 Konventioneller Treiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3.5 3-Level-Treiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.6 Treiber für SiC-MOSFET und IGBT . . . . . . . . . . . . . . . . . . . . . . . 45 4 Reduzierung der Treiberverluste durch Einschrittkommutierung 4.1 Einschrittkommutierung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 4.2 Stromvorzeichenerkennung . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 4.3 Berechnung der Verlustleistungen für den eingeschalteten Zustand des SiC- Bipolartransistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 4.4 Messung der Treiberverlustleistung . . . . . . . . . . . . . . . . . . . . . . . . 52 5 Charakterisierung des SiC-Bipolartransistors 5.1 Messaufbau für Untersuchung des Ein- und Ausschaltverhaltens . . . . . . . . 55 5.2 Doppelpulsverfahren . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 5.3 Definition der Schaltzeiten und Schaltverlustleistung . . . . . . . . . . . . . . 57 5.4 Messung der Schaltwärme . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 5.4.1 Spannungstastköpfe . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 5.4.2 Stromsensoren . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 5.4.3 Zeitliche Verschiebung der Messsignale . . . . . . . . . . . . . . . . . 62 5.4.4 Vergleich von konventionellem und 3-Level-Treiber . . . . . . . . . . . 65 5.4.5 Vergleich bei unterschiedlicher Treiberspannung . . . . . . . . . . . . 66 5.4.6 Vergleich bei halb und voll bestückter Halbbrücke . . . . . . . . . . . . 68 5.4.7 Vergleich von SiC-Bipolartransistor mit SiC-MOSFET und Si-IGBT . . 69 5.4.8 Reduzierung der Spannungsspitze beim Ausschalten . . . . . . . . . . 74 5.5 Simulation des Schaltverhaltens eines SiC-Bipolartransistors . . . . . . . . . . 79 5.5.1 Schaltverhalten bei Ansteuerung mit unipolarem Treiber . . . . . . . . 79 5.5.2 Simulation des Einfluss der Emitter-Induktivität auf Schaltwärme . . . 81 5.5.3 Vergleich von Simulation und Messung . . . . . . . . . . . . . . . . . 82 5.6 Durchlassverlustleistung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 6 Einsatz von SiC-Bipolartransistoren im Wechselrichter 6.1 Aufbau der Wechselrichter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 6.2 Inbetriebnahme des Wechselrichters . . . . . . . . . . . . . . . . . . . . . . . 89 6.3 Überspannungen an den Motorklemmen der 1 kW-Asynchronmaschine . . . . 91 6.4 Umbau des SiC-Wechselrichters . . . . . . . . . . . . . . . . . . . . . . . . . 93 6.5 Spannungsspitzen in der Ansteuerspannung . . . . . . . . . . . . . . . . . . . 94 6.6 Halbbrückenverluste im Leerlauf . . . . . . . . . . . . . . . . . . . . . . . . . 98 7 Zusammenfassung und Fazit 101 Literaturverzeichnis 104 A Anhang A.1 Netzliste für SiC-Bipolartransistor FSICBH057A120 . . . . . . . . . . . . . . 113 A.2 Leiterplatten für Doppelpuls-Test und SiC-Wechselrichter . . . . . . . . . . . . 114 A.3 Herleitung des Feldverlaufs in der Driftzone des gesperrten pn-Übergangs . . . 116 A.4 Herleitung des Emitterwirkungsgrads . . . . . . . . . . . . . . . . . . . . . . . 119 A.5 Herleitung des spezifischen Widerstands der Driftzone . . . . . . . . . . . . . 121 A.6 Lebenslauf von Henry Barth . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 A.6.1 Persönliche Angaben . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 A.6.2 Wissenschaftlicher Werdegang . . . . . . . . . . . . . . . . . . . . . . 124

The trend of electrification in transportation applications has led to the fast development of high-power-density power electronics converters. High-switching-frequency and high-temperature operations are the two key factors towards this target. Both requirements, however, are challenging the fundamental limit of silicon (Si) based devices. The emerging wide-bandgap, silicon carbide (SiC) power devices have become the promising solution to meet these requirements. With these advanced devices, the technology barrier has now moved to the compatible integration technology that can make the best of device capabilities in high-power-density converters. Many challenges are present, and some of the most important issues are explored in this dissertation. First of all, the high-temperature performances of the commercial SiC MOSFET are evaluated extensively up to 200 degree C. The static and switching characterizations show that the device has superior electrical performances under elevated temperatures. Meanwhile, the gate oxide stability of the device - a known issue to SiC MOSFETs in general - is also evaluated through both high-temperature gate biasing and gate switching tests. Device degradations are observed from these tests, and a design trade-off between the performance and reliability of the SiC MOSFET is concluded. To understand the interactions between devices and circuit parasitics, an experimental parametric study is performed to investigate the influences of stray inductances on the MOSFETs switching waveforms. A small-signal model is then developed to explain the parasitic ringing in the frequency domain. From this angle, the ringing mechanism can be understood more easily and deeply. With the use of this model, the effects of DC decoupling capacitors in suppressing the ringing can be further explained in a more straightforward way than the traditional time-domain analysis. A rule of thumb regarding the capacitance selection is also derived. A Power Electronics Building Block (PEBB) module is then developed with discrete SiC MOSFETs. Integrating the power stage together with the peripheral functions such as gate drive and protection, the PEBB concept allows the converter to be built quickly and reliably by simply connecting several PEBB modules. The high-speed gate drive and power stage layout designs are presented to enable fast and safe switching of the SiC MOSFET. Based on the PEBB platform, the state-of-the-art Si and SiC power MOSFETs are also compared in the device characteristics, temperature influences, and loss distributions in a high-frequency converter, so that special design considerations can be concluded for the SiC MOSFET. Towards high-temperature, high-frequency and high-power operations, integrated wire-bond phase-leg modules are also developed with SiC MOSFET bare dice. High-temperature packaging materials are carefully selected based on an extensive literature survey. The design considerations of improved substrate layout, laminated bus bars, and embedded decoupling capacitors are all discussed in detail, and are verified through a modeling and simulation approach in the design stage. The 200 degree C, 100 kHz continuous operation is demonstrated on the fabricated module. Through the comparison with a commercial SiC phase-leg module designed in the traditional way, it is also shown that the design considerations proposed in this work allow the SiC devices in the wire-bond structure to be switched twice as fast with only one-third of the parasitic ringing. To further push the performance of SiC power modules, a novel hybrid packaging technology is developed which combines the small parasitics and footprint of a planar module with the easy fabrication of a wire-bond module. The original concept is demonstrated on a high-temperature rectifier module with SiC JFET. A modified structure is then proposed to further improve design flexibility and simplify module fabrication. The SiC MOSFET phase-leg module built in this structure successfully reaches the switching speed limit of the device almost without any parasitic ringing. Finally, a new switching loop snubber circuit is proposed to damp the parasitic ringing through magnetic coupling without affecting either conduction or switching losses of the device. The concept is analyzed theoretically and verified experimentally. The initial integration of such a circuit into the power module is presented, and possible improvements are proposed. / Ph. D.

To summarize this entire thesis, MW-assisted spectroscopy has been proposed as a promising approach to investigate the optical properties of VSi and VV spin defects in 4H- and 6H-SiC. The MW-assisted spectroscopy has enabled to separate the spectrally overlapped contribution of different types of defects. From a PL spectrum containing no overlapping spectral contributions of other defects, the local vibrational mode of all measured VSi and VV in 4H- and 6H-SiC has been found along with the phonon energy and DW factor. The interaction of local vibrational modes with point defects has allowed to understand the spin, optical, mechanical, and thermal properties of these defects. In the investigation of V2 in 4H-SiC, a perfect agreement between the experimental data and theoretical calculation have been obtained. The MW-assisted spectra measured at different resonant frequencies associated with the same defect have been found to reveal the same vibrational mode and DW factor. Furthermore, some new ODMR lines to certain defects have been assigned, which have never been reported before. From the investigation of the V2 VSi in 6H-SiC, it has been found that the temperature does not have a clear influence on the DW factor, but high-fluence electron irradiation has been shown to decrease the DW factor. In the polarization investigation, it has been found that in 6H-SiC, V1 possesses no polarization, V2 shows a strong E||c-axis polarization, while V3 exhibits a strong E⊥c-axis polarization. It has also been demonstrated that the temperature and the orientation of the excitation laser have no influence on the photon polarization. In short, this thesis has demonstrated that MW-assisted spectroscopy is a powerful technique to investigate a large number of spin defects in wide-bandgap semiconducting materials.

Silicon Carbide, a wide band gap (WBG) semiconductor, has pushed electrical limits beyond Silicon (Si) when it comes to power electronics. It has offered the electrification of society showing promise for a greener future. However, owing to higher material defects, particularly at the oxide/semiconductor interface, threshold voltage (VTH) instability has been a persistent problem. This thesis examines the drift in VTH when a bipolar ac gate bias stress is applied to 4H-SiC MOSFETs. For this purpose, a gate stress setup using a gate driver IC is created. This is followed by a measure-stress-measure (MSM) sequence at varying gate voltages to study the effects of VGS,on, VGS,off, and voltage overshoots on the drift. Two critical VGS,off biases are found. The drift is negligible until the first critical point, accelerated, between the first and second bias, and decelerated beyond the second point with degradation of the oxide. Overshoots/undershoots in the gate drive loop shows an excess drift of 37.77% with only undershoots contributing entirely to this percentage. Drift at higher temperature is smaller than at room temperature but with changing slope. After 400 hours of stress at +18/ − 8V, a VTH drift of 17.5% while a RDS,on drift of only 2.5 % is measured. End of life VTH for devices in this thesis show a drift of 280mV at the automotive application switching limit and 500mV at the solar applications switching limit. The findings are intended for better understanding of device performance limits at high switching cycles and voltage biases. / Bredbandgapsmaterialet kiselkarbid har utvidgat gränserna för kraftelektronikens elektriska prestanda jämfört med vad som går att åstadkomma med kisel. Kiselkarbiden har gett nya möjligheter för samhällets elektrifiering vilket är lovande för en grön framtid. På grund av materialdefekter speciellt vid gränsytan mellan kiselkarbid (SiC) och kiseldioxid har det varit ett bestående problem med drivande tröskelspänning. Det här examensarbetet undersöker drift för tröskelspänningen då gate-terminalen i en 4H-SiC MOSFET utsätts för en bipolär alternerande spännings-stress. För detta ändamål har en mätuppställning med en IC-krets för gate-styrning byggts upp. Detta följs av en mät-stress-mät sekvens för varierande gate-source spänningar (VGS) för att studera effekter av VGS,on,VGS,off och spännings-överslängar på tröskelspänningsdriften. Två kritiska nivåer för VGS,off har påvisats. Tröskelspänningsdriften är försumbar före den första nivån, accelererad mellan den första och andra nivån, och retarderad efter den andra nivån med degradering av gate-oxiden. För överslängar och underslängar i gate-spänningen syns en extra tröskelspänningsdrift på 37.77 % där enbart underslängarna bidrar till driften. Tröskelspänningsdriften vid högre temperatur är mindre än vid rumstemperatur men med förändrad lutning för subtröskelspänningskarakteristiken. Efter 400 timmars stress med +18V/-8V, uppmättes en tröskelspänningsdrift på 17.5 % men endast 2.5 % drift för on-resistansen. Vid slutet av förväntad livstid i form av switch-cykler uppmättes 280 mV drift för biltillämpningar och 500 mV för solpanelstillämpningar. Resultaten är ämnade att förbättra förståelsen för komponentprestandans begränsningar efter ett stort antal switch-cykler och olika gate-source spänningar.

This paper describes work related to the “Miniature Student Satellite” (MIST) project and the ”SiC in Space” project, located at KTH, Stockholm, Sweden. The goal of the MIST project is to launch KTH’s first student satellite into space, carrying multiple scientific experiments where SiC in Space is included. This thesis contains a compilation of three MIST-related bachelor theses that were carried out at KTH in the spring of 2016, primarily consisting of constructing and testing circuits for power supply and measurements for the SiC in Space part of the satellite. A printed circuit board has been developed, which accommodates experiment circuits to evaluate the features and functionality of silicon carbide components in a space environment, and power the supply to the SiC in Space and the Piezo LEGS projects. The development includes designing, assembling and testing the PCB according to the MIST team’s demands and requirements. Emphasis has been laid on electrical safety to ensure that the design can not short circuit the satellite battery, as well as EMC considerations to minimize the EMI between different parts of the satellite. Final testing of the hardware has not been executed due to an ordering error and time shortage, wherefore the planned test protocol has been included for future work. / Denna kandidatuppsats beskriver arbete relaterat till “Miniature Student Satellite” (MIST)-, samt SiC in Space-projekten, vid KTH, Stockholm, Sverige. MIST-projektets mål är att skicka KTH:s första studentsatellit till rymden, där SiC in Space är ett av flera medföljande vetenskapliga experiment. Detta projekt sammanställer tre examensarbeten relaterade till MIST som genomfördes vid KTH under våren 2016, huvudsakligen bestående av att konstruera och testa kretsar för strömförsörjning samt mätningar för SiC in Space-delen av satelliten. Ett kretskort som innehåller experimentkretsar för att utvärdera egenskaper och funktionalitet för komponenter av materialet kiselkarbid i en rymdmiljö, samt strömförsörjningskretsar till SiC in Space- och Piezo LEGS-projekten har utvecklats. Utvecklingen omfattar design, montering and testning av kretskortet enligt MIST-gruppens krav. Tonvikt har lagts på elsäkerhet för att säkerställa att designen inte kan kortsluta satellitens batteri, såväl som EMC för att minimera EMI mellan olika delar av satelliten. Slutgiltig testning av hårdvaran har ej kunnat genomföras på grund av tidsbrist beroende på ett beställningsfel. Därför har det planerade testprotokollet inkluderats för framtida arbete.

GaN-HEMTs (Gallium Nitride-based High Electron Mobility Transistors) have, thanks to the large band gap of GaN, electrical properties that are suitable for applications of high electrical voltages, high currents, and fast switching. The large band gap also gives GaN-HEMTs a high resistance to radiation. In this degree project, the effects of 2 MeV proton irradiation of GaN-HEMTs constructed on both silicon carbide and silicon substrates are investigated. 20 transistors per substrate were irradiated in the particle accelerator 5 MV NEC Pelletron in the Ångström laboratory at Uppsala University. These transistors were exposed to radiation doses in the range of 10^11 to 10^15 protons/cm^2. The analysis shows that both transistors on silicon, as well as silicon carbide, are unaffected by proton irradiation up to a dose of 10^14 protons/cm^2. GaN-on-Si transistors show less influence of radiation than GaN-on-SiC transistors. The capacitances between gate and drain as well as drain and source for both GaN-on-SiC and GaN-on-Si HEMTs show hysteresis as a function of forward and backward gate voltage sweeps for the radiation dose of 10^15 protons/cm^2. / GaN-HEMTs (Galliumnitridbaserade High Electron Mobility Transistors) har tack vare det stora bandgapet i GaN goda elektriska egenskaper som lämpar sig för höga elektriska spänningar, höga strömmar och snabb växling mellan av- och på-tillstånd. Det stora bandgapet ger även GaN-HEMTs ett stort motstånd mot strålning.I detta examensarbete undersöks effekterna av 2 MeV protonbestrålning av GaN-HEMTs. Dessa HEMTs är konstruerade på både kiselkarbid- och kiselsubstrat.20 transistorer per transistorsubstrat bestrålades i partikelacceleratorn 5 MV NEC Pelletron i Ångströmslaboratoriet vid Uppsala Universitet. Dessa transistorer utsattes för strålningsdoser inom intervallet 10^11 till 10^15 protoner/cm^2. Resultaten visar att både tranisistorer på kisel såsom kiselkarbid är opåverkade av strålning upp till en dos av 10^14 protoner/cm^2. GaN-på-Si-transistorer visar en mindre påverkan av protonstrålning än GaN-på-SiC-transistorer. Ytterligare uppstod hysteresis för kapacitanser mellan gate och drain och mellan gate och source som en funktion av fram- och bakriktad gate-spänning efter en strålningsdos av 10^15 protoner/cm^2.

Silicon is the main material used in electronics. The evolution of power electronics and the need for more power efficient semiconductor devices led silicon to its limits. Silicon carbide is a promising material for electronic applications with a wide band-gap, high critical electric field, high thermal conductivity and saturation velocity. Except from its superiority to silicon, silicon carbide comes with a drawback of about two orders of magnitude more interface traps in the SiC/SiO2 interface compared with silicon. A result of this drawback is a flat-band voltage shift when applying a stress to the gate of MOS capacitors and power MOSFETs. In order to study the pure characteristics of the SiC/SiO2 interface, two stress methods, a current pulse stress and gate voltage upsweep, have been applied on 4H-SiC capacitors with nitrided thermal oxides at room temperature and at higher temperatures. The flat-band voltage recovery was examined. The flat-band voltage could be restored at room temperature with a gate voltage downsweep while a restoration is not needed at higher temperatures. The maximum voltage (initial voltage) and the voltage rate of the downsweep were investigated and higher initial voltages and lower voltage rates showed to lead to better VFB restoration. A 200 millisecond long current pulse stress was implemented and it had almost similar effects as the voltage upsweep which lasts 50 seconds. / Kisel är det viktigaste materialet som används i elektronik. Utvecklingen av kraftelektronik och behovet av mer energieffektiva halvledarkomponenter ledde kisel till sina gränser. Kiselkarbid är ett lovande material för elektroniska applikationer med ett brett bandgap, högt kritiskt elektriskt fält, hög värmeledningsförmåga och hög mättningshastighet. Förutom dess överlägsenhet gentemot kisel, kommer kiselkarbid med en nackdel med cirka två storleksordningar fler gränssnittsfällor i SiC / SiO2-gränssnittet jämfört med kisel. Ett resultat av denna nackdel är en förskjutning av flatbands-spänningen, VFB, när man applicerar en spänning på gaten till MOS-kondensatorer och kraft- MOSFETar. För att studera de rena egenskaperna hos SiC/SiO2-gränssnittet har två spänningsmetoder, en strömpulsstress och ett uppåtriktat gate-spänningssvep, applicerats på 4H-SiC- kondensatorer med nitriderade termiska oxider vid rumstemperatur och vid högre temperaturer. Återställning av VFB undersöktes. VFB kan återställas vid rumstemperatur med ett nedåtriktat gate-spänningssvep medan en återställning inte behövs vid högre temperaturer. Den maximala spänningen (initialspänningem) och svephastigheten för det nedåtriktade svepet undersöktes och högre initialspänningar och lägre svephastigheter visade sig leda till bättre VFB-återställning. En 200 millisekund lång strömpuls-stress implementerades och den hade nästan samma effekter som ett uppåtriktat spänningssvep

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