Excess Carrier Phenomenon in Semiconductors

Abstract

The generation of excess carriers in a semiconductor may be accomplished by either electrical or optical means. For example, electron--hole pairs are created in a semiconductor when photons with energies exceeding the band gap energy of the semiconductor are absorbed. Similarly, minority carrier injection can be achieved by applying a forward bias voltage across a p-n junction diode or a bipolar junction transistor. The inverse process to the generation of excess carriers in a semiconductor is that of recombination. The annihilation of excess carriers generated by optical or electrical means in a semiconductor may take place via different recombination mechanisms. Depending on the ways in which the energy of an excess carrier is removed during a recombination process, there are three basic recombination mechanisms that are responsible for carrier annihilation in a semiconductor. They are (1) nonradiative recombination (i.e., the multiphonon process), (2) band-to-band radiative recombination, and (3) Auger band-to-band recombination.