ABSTRACT
Photodetectors (PDs) convert light energy into electrical energy, which usually manifests as a photocurrent. This chapter gives an introduction to the working principle of photodetection by semiconductors, the material properties, different types, and their structures, important parameters pertaining to PDs, and materials and makes a list of the application areas. The conversion of optical energy into electrical energy by a PD involves three basic processes. First, a bunch of incident photons is absorbed by the semiconducting material to create excess electron–hole pairs. The carriers are then transported across the absorption or transit region. In the third stage, the transported carriers are collected to generate photocurrent. The absorption process in a direct gap semiconductor is indicated by a vertical line in the E-k diagram. Since a photon and a phonon are involved in the absorption process, the second-order perturbation theory is used to calculate the absorption coefficient in indirect gap semiconductors.
