In this chapter, we consider generation and recombination processes in semiconductors. In a semiconductor, electrons and holes can be either generated or recombined within a given volume, thereby changing the local carrier concentrations. In a sense, there are sources and sinks of particles within the semiconductor itself. Although generation and recombination events change the local carrier concentrations, the entire semiconductor must always remain space-charge neutral. This requirement leads to the injection or extraction of charge at the contacts. In this chapter, we examine the different types of generation and recombination processes and outline their behaviors.

Basic Generation-Recombination Mechanisms

There are in general three basic generation–recombination channels available in semiconductors. These are

1. Auger,

2. radiative,

3. thermal.

These mechanisms are defined as follows.

An Auger process is defined as an electron–hole pair (EHP) recombination followed by a transfer of energy from the recombined EHP to a free carrier, which is then excited to high energy within the band. The inverse Auger effect, in which an EHP is produced, is called impact ionization. In this case, a high-energy free carrier collides with the lattice and transfers its excess kinetic energy to an electron in the valence band, promoting it to the conduction band. Hence an EHP is produced after the event.

In a radiative recombination event, an EHP recombines with the emission of a photon. The electron recombines from the conduction band with a hole in the valence band.