ABSTRACT
One of the primary motivations for studying nanometer-scale semiconductor crystallites, or nanocrystals, is to understand what happens when a semiconductor becomes small. To review recent progress in utilizing optical spectroscopy to understand this size dependence, this chapter begins with a discussion of the basic theoretical concepts necessary to understand electronic structure in nanocrystals. It describes the experimental data from the prototypical direct gap semiconductor system, cadmium selenide. The chapter explains the origin of this phenomenon and discusses recent work that moves beyond cadmium selenide (CdSe). It outlines some of the remaining issues in the electronic structure of nanocrystals. For many semiconductors, the diamond-like band structure is a good approximation. In the particular case of CdSe, two additional complications arise. First, ignores the crystal field splitting that occurs in materials with a wurtzite (or hexagonal) lattice. The second complication is that, unlike the diamond structure, the hexagonal CdSe lattice does not have inversion symmetry.
