Investigation of device performance limiting defects in silicon carbide semiconductor

The presence of various crystallographic defects in commercially available material limits the wide commercialization of SiC devices. These defects are known to significantly affect device characteristics such as leakage current, breakdown voltage and forward voltage. Hence the identification and investigation of defects influencing device performance is of vital importance.; This dissertation is devoted to investigation and identification of crystallographic defects in SiC bipolar and unipolar devices. Special attention is paid to studying of crystallographic defects in bipolar diodes formed by epitaxial process and diffusion. The Electron Beam Induced Current (EBIC) mode of Scanning Electron Microscope in accompaniment with other methods of defect investigation was used as the major tool for identification and analysis of the electrical activity of crystallographic defects. Their impact on the current-voltage characteristics of bipolar and unipolar devices will be discussed. Results presented in this dissertation give the possibility to provide recommendations for the identification of defects in these devices.; In the first chapter, an introduction to the material properties of SiC is given. Also the basic techniques of bulk and epitaxial growth of this material are briefly described. The second chapter includes the discussion about basic principles of dislocation theory and further description of major types of defects in SiC as well as reasons for their generation. Special attention in this chapter will be paid to description of such specific defects as Stacking Faults and partial dislocations. The issues related to the interaction of impurities with extended defects also are considered. Chapter three mainly concerns the electrical properties of crystallographic defects. Particularly, electronic properties (obtained from theory and experiment) of "clean" and "contaminated by impurities" stacking faults and C- and Si-core basal dislocations in SiC are discussed in detail. Electronic properties of threading dislocations (screw and edge type) are also discussed. Mechanism of recombination enhanced reactions in SIC is described. In the fourth chapter a review of basic techniques of investigation of crystallographic defects in SiC is presented. In the fifth chapter the principles of Electron Beam Induced Current technique are defined in detail. Particularly, interaction of electrons with material as well electron beam induced signal on defect and defect free material are described. Chapter six presents experimental results of investigation of crystallographic defects in unipolar and bipolar structures. Mechanisms of leakage current in these structures and correlation with specific defects in SiC are discussed in the next chapter, where our experimental results regarding the impact of specific defects on leakage current for diffused p-i-n junctions also are shown. Finally, in the concluding chapter, the key aspects relevant to defect investigation in SiC, developed in this dissertation, are summarized. Suggestions for future research are provided.