Annealing-Induced Changes in the Nature of Point Defects in Sublimation-Grown Cubic Silicon Carbide

In recent years, cubic silicon carbide (3C-SiC) has gained increasing interest as semiconductor material for energy saving and optoelectronic applications, such as intermediate-band solar cells, photoelectrochemical water splitting, and quantum key distribution, just to name a few. All these applications critically depend on further understanding of defect behavior at the atomic level and the possibility to actively control distinct defects. In this work, dopants as well as intrinsic defects were introduced into the 3C-SiC material in situ during sublimation growth. A series of isochronal temperature treatments were performed in order to investigate the temperature-dependent annealing behavior of point defects. The material was analyzed by temperature-dependent photoluminescence (PL) measurements. In our study, we found a variation in the overall PL intensity which can be considered as an indication of annealing-induced changes in structure, composition or concentration of point defects. Moreover, a number of dopant-related as well as intrinsic defects were identified. Among these defects, there were strong indications for the presence of the negatively charged nitrogen vacancy complex (NC–VSi)−, which is considered a promising candidate for spin qubits

Potential and challenges of compound semiconductor characterization by application of non-contacting characterization techniques

Trotz der im Vergleich zu Silizium überragenden elektronischen Eigenschaften von Verbindungshalbleitern, ist die Leistung der daraus gefertigten elektrischen Bauelemente aufgrund der vorhandenen, die elektronischen Materialeigenschaften beeinflussenden Defekte nach wie vor begrenzt. Die vorliegende Arbeit trägt dazu bei, das bestehende ökonomische Interesse an einem besseren Verständnis der die Bauelementeleistung limitierenden Defekte zu befriedigen, indem sie die Auswirkungen dieser Defekte auf die elektronischen und optischen Materialeigenschaften von Indiumphosphid (InP) und Siliziumkarbid (SiC) aufzeigt. Zur Klärung der Effekte finden in der Arbeit sich ergänzende elektrische und optische Charakterisierungsmethoden Anwendung, von denen die meisten kontaktlos und zerstörungsfrei arbeiten und sich daher prinzipiell auch für Routineanalysen eignen. Die erzielten Ergebnisse bestätigen und ergänzen Literaturdaten zum Defektinventar in InP und SiC nutzbringend. So wird insbesondere das Potential der elektrischen Charakterisierung mittels MDP und MD-PICTS, welche in der Arbeit erstmals für die Defektcharakterisierung von InP und SiC eingesetzt wurden, nachgewiesen. Die experimentellen Studien werden dabei bedarfsorientiert durch eine theoretische Betrachtung des entsprechenden Signalentstehungsmechanismuses ergänzt.:1 Motivation 2 Theses 3 Compound semiconductors: structure and benefits 4 Growth of compound semiconductors 5 Structural defects in compound semiconductors 6 Defects and their impact on electronic material properties 7 Effect of annealing treatments on the properties of InP 8 Experimental details 9 Experimental results 10 Summary of the thesis 11 Conclusion and impact 12 Prospect of future work 13 Appendix - Theory of signal development 14 List of tables 15 List of figures 16 List of abbreviations and symbols 17 Eidesstattliche Erklärung - Declaration of academic honesty 18 Danksagung - Acknowledgment 19 Veröffetnlichungen - Publications 20 ReferencesAlthough the electronic properties of compound semiconductors exceed those of Silicon, the performance of respective electronic devices still is limited. This is due to the presence of various growth-induced defects in compound semiconductors. In order to satisfy the economic demand of an improved insight into limiting defects this thesis contributes to a better understanding of material inherent defects in commonly used Indium Phosphide (InP) and Silicon Carbide (SiC) by revealing their effects on electronic and optical material properties. On that account various complementary electrical and optical characterization techniques have been applied to both materials. Most of these techniques are non-contacting and non-destructive. So, in principle they are qualified for routine application. Characterization results that are obtained with these techniques are shown to either confirm published results concerning defects in InP and SiC or beneficially complement them. Thus, in particular the potential of electrical characterization by MDP and MD-PICTS measurements is proofed. Both techniques have been applied for the first time for defect characterization of InP and SiC during these studies. The respective experiments are complemented by a theoretical consideration of the corresponding signal development mechanism in order to develop an explanation approach for occasionally occurring experimental imperfection also arising during silicon characterization from time to time.:1 Motivation 2 Theses 3 Compound semiconductors: structure and benefits 4 Growth of compound semiconductors 5 Structural defects in compound semiconductors 6 Defects and their impact on electronic material properties 7 Effect of annealing treatments on the properties of InP 8 Experimental details 9 Experimental results 10 Summary of the thesis 11 Conclusion and impact 12 Prospect of future work 13 Appendix - Theory of signal development 14 List of tables 15 List of figures 16 List of abbreviations and symbols 17 Eidesstattliche Erklärung - Declaration of academic honesty 18 Danksagung - Acknowledgment 19 Veröffetnlichungen - Publications 20 Reference

Physical parameterisation of 3C-Silicon Carbide (SiC) with scope to evaluate the suitability of the material for power diodes as an alternative to 4H-SiC

Major recent developments in growth expertise related to the cubic polytype of Silicon Carbide, the 3C-SiC, coupled with its remarkable physical properties and the low fabrication cost, suggest that within the next five years, 3C-SiC devices can become a commercial reality. It is therefore important to develop Finite Element Method (FEM) techniques and models for accurate device simulation. Furthermore, it is also needed to perform an exhaustive simulation investigation with scope to identify which family of devices, which voltage class and for which applications this polytype is suited. In this paper, we present a complete set of physical models and material parameters for bulk 3C-SiC aiming Technology Computer Aided Design (TCAD) tools. These are compared with those of 4H-SiC, the most well developed polytype of SiC. Thereafter, the newly developed material parameters are used to assess 3C- and 4H-SiC vertical power diodes, P-i-N and Schottky Barrier Diodes (SBDs), to create trade-off maps relating the on-state voltage drop and the blocking capability. Depending on the operation requirements imposed by the application, the developed trade-off maps set the boundary of the realm for those two polytypes. It also allows us to predict which applications will benefit from an electrically graded 3C-SiC power diodes

Design, fabrication and characterization of III-nitride PN junction devices

Design, fabrication and characterization of III-Nitride pn junction devices Jae Boum Limb 94 pages Directed by Dr. Russell D. Dupuis This dissertation describes an investigation of three types of III-nitride (AlInGaN) based p-n junction devices that were grown by metalorganic chemical vapor deposition (MOCVD). The three types of devices are Ultra-Violet (UV) avalanche photodiodes (APDs), green light emitting diodes (LEDs), and p-i-n rectifiers. For avalanche photodiodes, a material growth on low-dislocation density GaN substrates, processed with low-damage etching receipes and high quality dielectric passivations, were proposed. Using this technology, GaN APDs with optical gains greater than 3000, and AlGaN APDs showing true avalanche gains have been demonstrated. For green LEDs, the use of InGaN:Mg as the p-layer, rather than employing the conventional GaN:Mg has been proposed. Green LEDs with p-InGaN have shown higher emission intensities and lower diode series resistances compared to LEDs with p-GaN. Using p-InGaN layers, LEDs emitting at green and longer wavelengths have been realized. For p-i-n rectifiers, design, fabrication and characterization of device structures using the conventional mesa-etch configuration, as well as the full-vertical method have been proposed. High breakdown devices with low on-resistances have been achieved. Specific details on device structures, fabrication methods, and characterization results are discussed.Ph.D.Committee Chair: Russell Dupuis; Committee Member: David Citrin; Committee Member: Joy Laskar; Committee Member: Srinivas Garimella; Committee Member: William Doolittl

Design, Fabrication and Characterization of GaN HEMTs for Power Switching Applications

The unique properties of the III-nitride heterostructure, consisting of gallium nitride (GaN), aluminium nitride (AlN) and their ternary compounds (e.g. AlGaN, InAlN), allow for the fabrication of high electron mobility transistors (HEMTs). These devices exhibit high breakdown fields, high electron mobilities and small parasitic capacitances, making them suitable for wireless communication and power electronic applications. In this work, GaN-based power switching HEMTs and low voltage, short-channel HEMTs were designed, fabricated, and characterized.In the first part of the thesis, AlGaN/GaN-on-SiC high voltage metal-insulator-semiconductor (MIS)HEMTs fabricated on a novel ‘buffer-free’ heterostructure are presented. This heterostructure effectively suppresses buffer-related trapping effects while maintaining high electron confinement and low leakage currents, making it a viable material for high voltage, power electronic HEMTs. This part of the thesis covers device processing techniques to minimize leakage currents and maximize breakdown voltages in these ‘buffer-free’ MISHEMTs. Additionally, a recess-etched, Ta-based, ohmic contact process was utilized to form low-resistive ohmic contacts with contact resistances of 0.44-0.47 Ω∙mm. High voltage operation can be achieved by employing a temperature-stable nitrogen implantation isolation process, which results in three-terminal breakdown fields of 98-123 V/μm. By contrast, mesa isolation techniques exhibit breakdown fields below 85 V/μm and higher off-state leakage currents. Stoichiometric low-pressure chemical vapor deposition (LPCVD) SiNx passivation layers suppress gate currents through the AlGaN barrier below 10 nA/mm over 1000 V, which is more than two orders of magnitude lower compared to Si-rich SiNx passivation layers. A 10% dynamic on-resistance increase at 240 V was measured in HEMTs with stoichiometric SiNx passivation, which is likely caused by slow traps with time constants over 100 ms. SiNx gate dielectrics display better electrical isolation at high voltages compared to HfO2 and Ta2O5. However, the two gate oxides exhibit threshold voltages (Vth) above -2 V, making them a promising alternative for the fabrication of recess-etched normally-off MISHEMTs.Reducing the gate length (Lg) to minimize losses and increase the operating frequency in GaN HEMTs also entails more severe short-channel effects (SCEs), limiting gain, output power and the maximum off-state voltage. In the second part of the thesis, SCEs were studied in short-channel GaN HEMTs using a drain-current injection technique (DCIT). The proposed method allows Vth to be obtained for a wide range of drain-source voltages (Vds) in one measurement, which then can be used to calculate the drain-induced barrier lowering (DIBL) as a rate-of-change of Vth with respect to Vds. The method was validated using HEMTs with a Fe-doped GaN buffer layer and a C-doped AlGaN back-barrier with thin channel layers. Supporting technology computer-aided design (TCAD) simulations indicate that the large increase in DIBL is caused by buffer leakage. This method could be utilized to optimize buffer design and gate lengths to minimize on-state losses and buffer leakage currents in power switching HEMTs

Electrical leakage phenomenon in heteroepitaxial cubic silicon carbide on silicon

© 2018 Author(s). Heteroepitaxial 3C-SiC films on silicon substrates are of technological interest as enablers to integrate the excellent electrical, electronic, mechanical, thermal, and epitaxial properties of bulk silicon carbide into well-established silicon technologies. One critical bottleneck of this integration is the establishment of a stable and reliable electronic junction at the heteroepitaxial interface of the n-type SiC with the silicon substrate. We have thus investigated in detail the electrical and transport properties of heteroepitaxial cubic silicon carbide films grown via different methods on low-doped and high-resistivity silicon substrates by using van der Pauw Hall and transfer length measurements as test vehicles. We have found that Si and C intermixing upon or after growth, particularly by the diffusion of carbon into the silicon matrix, creates extensive interstitial carbon traps and hampers the formation of a stable rectifying or insulating junction at the SiC/Si interface. Although a reliable p-n junction may not be realistic in the SiC/Si system, we can achieve, from a point of view of the electrical isolation of in-plane SiC structures, leakage suppression through the substrate by using a high-resistivity silicon substrate coupled with deep recess etching in between the SiC structures

Realistic simulation of forward and reverse characteristics of 4H-SiC pn junction diode

Master'sMASTER OF ENGINEERIN

Electrical Activation Studies of Ion Implanted Gallium Nitride

A comprehensive and systematic electrical activation study of Si-implanted GaN was performed as a function of ion implantation dose, anneal temperature, and implantation temperature. Additionally, Mg-implanted GaN was also investigated. Temperature-dependent Hall effect measurements and photoluminescence (PL) spectra were used to characterize the samples. GaN wafers capped with AlN were implanted with Si ions at doses ranging from 1x1013 to 5x1015 cm-2 and annealed from 1050 to 1350 °C. The optimum anneal temperature for samples implanted with the higher Si doses is around 1350 °C, exhibiting nearly 100% electrical activation efficiency. Exceptional mobilities and carrier concentrations were obtained on all Si-implanted samples. PL spectra revealed nearly complete implantation damage recovery as well as the nature of the yellow luminescence plaguing nearly all Si-doped GaN. Additionally, GaN wafers were implanted with Mg and various coimplants and annealed from 1100 to 1350 °C. All of the Mg-implanted and most of the Mg-coimplanted GaN samples became extremely resistive, and did not show definite p-type conductivity even after annealing at 1350 °C, remaining highly resistive even at a sample temperature as high as 800 K. A dominant 2.36 eV green luminescence band observed in the PL spectra of all Mg-implanted samples is attributed to a Mg-related deep complex DAP transition. The inefficient electrical activation of Mg acceptors implanted into GaN is attributed to these Mg-related deep complexes

Feature Papers in Electronic Materials Section

This book entitled "Feature Papers in Electronic Materials Section" is a collection of selected papers recently published on the journal Materials, focusing on the latest advances in electronic materials and devices in different fields (e.g., power- and high-frequency electronics, optoelectronic devices, detectors, etc.). In the first part of the book, many articles are dedicated to wide band gap semiconductors (e.g., SiC, GaN, Ga2O3, diamond), focusing on the current relevant materials and devices technology issues. The second part of the book is a miscellaneous of other electronics materials for various applications, including two-dimensional materials for optoelectronic and high-frequency devices. Finally, some recent advances in materials and flexible sensors for bioelectronics and medical applications are presented at the end of the book