Advanced Characterization Techniques

The structural, electrical and optical characterization of silicon and silicon devices can be presently carried out with a variety of techniques, which are often used at the industrial level without a deep understanding of the physical processes that are involved in obtaining the final data. The main aim of this Chapter is to direct the reader to a comprehensive understanding of the physical backgrounds of a few advanced electrical and optical measurements that are currently used to investigate the optoelectronic properties of silicon, with a major concern to the extension of these measurements to the micro- and nanolevel, particularly interesting for the study of extended defects like dislocations and precipitates as well as of silicon quantum dots and nanowires. As shown in previous chapters of this book, extended defects like grain boundaries and dislocations have a strong negative impact on the behavior of silicon-based devices, but third-generation solar cells (see Chapter 10) will use nanostructured features to overcomethe Shockley–Queisser limit or the detailed balance limit [1] to conversion efficiency of silicon solar cells. Nanostructured PV devices offer, in fact, the opportunity to engineer the photon absorption, the free-carrier generation and the carrier-extraction pathways independently of each other. A variety of nanostructures can be used to achieve these objectives including heterostructures, quantum dots and nanowires. In these materials,excitons are separated into free electrons and holes at the heterointerfaces. To work well, however, they require high-quality interfaces structured in three dimensions, along with good connectivity and transport properties in both the donor and acceptor regions.