Electron Paramagnetic Resonance Characterization of SiC
Electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for studying the physical and chemical structure of point defects in crystalline semiconductors. Investigations throughout the past few decades have provided detailed descriptions of so
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Electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for studying the physical and chemical structure of point defects in crystalline semiconductors. Investigations throughout the past few decades have provided detailed descriptions of some of the most important intrinsic defects and impurities in silicon carbide. Several reviews summarize the significant findings. This chapter expands the scope of earlier work by focusing on EPR studies of as-grown electronic-grade SiC. Both intrinsic and extrinsic defects pertinent to devices are discussed. In particular, impurities used to produce n- and p-type wafers and those incorporated to yield semi-insulating SiC are reviewed. In addition, defects generated by ion implantation are also discussed. To avoid repetition of previously published reviews, the physical description of the defects is only briefly summarized. Rather, this chapter emphasizes the use of collaborative techniques to determine defect energy levels and electricalpassivation mechanisms. Overall, the chapter highlights the contribution of EPR to understanding the electrical, physical, and chemical processes important to technological applications of silicon carbide.
7.1 Introduction Electron paramagnetic resonance (EPR) spectroscopy has been used since the fifties to study electronic materials such as Si, the II-VI semiconductors, and GaAs. EPR, or electron spin resonance (ESR) as it sometimes called, utilizes the absorption of microwaves by a point defect to determine the detailed electronic structure and symmetry. Since the signal obtained is a response to changes in magnetic dipole orientation (ie. a 'spin-flip'), only paramagnetic defects may be detected. That is, the EPR signal intensity is proportional to the number of defects with unpaired electrons. The magnetic interactions among the electron, local environment and applied magnetic field enable one to paint a detailed picture of the chemical and physical structure of a defect. Z. C. Feng (ed.), SiC Power Materials © Springer-Verlag Berlin Heidelberg 2004
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M.E. Zvanut
For instance, from analysis of EPR spectra at various temperatures and orientations the boron acceptor in SiC is generally thought to substitute for Si at the hexagonal site with the hole situated primarily on a nearest neighbor C. Many texts describe the theoretical basis and basic applications of EPR for a variety of semiconductor systems, including SiC [1-6]. The work presented below concentrates exclusively on the defects pertinent to device applications, and the description of the technique is limited to aspects that will enable the interested reader to determine the applicability of EPR to their problem. As a result, no information will be provided which enables a novice to measure spectra and interpret the results. Only the rudimentary steps needed to paint a picture of a defect from measured EPR spectra is presented. For details, the reader is referred to several excellent texts, particularly [1-3]. The chapter is divided into four sections. Section 7.1
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