ABSTRACT
The optical properties of semiconductors are inextricably linked to the electronic and vibrational properties. As we discussed in Chapter 1, the band gaps of semiconductors span a wide spectral range that can be exploited for the emission or detection of light. Along with intrinsic optical properties, defects give rise to various optical phenomena. Electronic transitions from hydrogenic impurities (Chapter 4) and vibrational modes of mass defects (Chapter 5) lead to well-defined peaks in the infrared (IR) spectrum that provide information about the symmetry and chemical composition of the defects. Optical spectra also provide researchers with a nondestructive method for determining the concentration of specific impurities in a sample. In this chapter, we continue the discussion of optical properties of defects in semi-
conductors. The first two sections deal with optical changes due to free carriers and their interaction with the lattice. The following sections cover the absorption and emission of photons with energies near the band gap. These processes involve the creation and destruction of electron-hole pairs. Finally, we discuss the optical properties of specific defect systems: isoelectronic impurities, large-relaxation defects such as DX centers, and transition metals.
