Page 86 - Photonics Essentials an introduction with experiments

Photoconductivity

80 Photonic Devices

Figure 5.2. Energy-level diagram for a simple GaAs photoconductor based on interband
absorption of light.

shown in Figure 5.1. Photoconductivity occurs when incident light
with an energy greater than the band gap is absorbed. The electron
hole pairs that are thus created increase the conductivity by increas-
ing the number of charge carriers. A schematic energy level diagram
of this structure is shown in Fig. 5.2.
The absorption of a photon having at least the band gap energy
creates an electron–hole pair, as shown in Fig. 5.3. In the example
that follows, we will use GaAs for the semiconductor material. In

Figure 5.3. A photon is absorbed by GaAs, creating an electron–hole pair. The conduc-
tivity of the GaAs is increased because there are more charge carriers.

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