Engineering Physics

8.20 Photodiodes

A photo diode is a reverse biased semiconductor p-n diode whose reverse current increases with the increase in intensity of light incident at the junction. When light is incident on the p-n junction of a photo diode, the atoms at the junction absorb the energy of photons and create more free electrons and holes. These additional carriers increase the reverse current. As the intensity of incident light on the junction increases the reverse current also increases. The basic biasing arrangement and construction of a photodiode is shown in Fig. 8.34(a). Its standard symbol is shown in Fig. 8.34(b). The lens is used to concentrate the light to the junction region.

 

Figure 8.34 (a) The basic biasing arrangement and construction of ...