TABLE OF CONTENTS In Chap. 6 we studied the interactions between a semiconductor and an electromagnetic field in which the semiconductor is brought from the ground state to an excited state via absorption of photons from the applied radiation. In this chapter we study other important optical phenomena in semiconductors. These optical processes involve emission of radiation from the sample. One of these processes is luminescence, while the other is inelastic scattering of light (also known as Raman or Brillouin scattering; their difference will be discussed later in this chapter). In a typical luminescence process electrons in the sample are excited electrically or optically. After some energy loss (relaxation) the excited electrons return to the ground state while emitting light. In a Raman or Brillouin process light is scattered by fluctuations inside the sample. One important difference between these two processes is that luminescence involves real excitation of electrons, while in light scattering typically virtual excitations of electrons are sufficient. We shall study the physical mechanisms of these processes in this chapter. We begin with a discussion of luminescence.
In order for a sample to emit radiation it has to be energized by some external means. One possible way is to excite the sample by injection of electrons and holes via an external current, leading to electroluminescence. Another common method is by absorption of photons of energy higher than that of the bandgap, the resulting process, in which photons of energy lower than the exciting...
