Question

In a photo diode, the conductive increases when the material is exposed to light. It is found that the conductivity changes only if the wavelength is less than 620 nm. What is the band gap?

Answer 1

Explanation:

• There will be an increase in any material’s conductivity when there is an increase in the free charge carriers.
• In the diode, extra electron hole pairs are formed when there is an exposure of photo diode to light, thus increasing the conductivity.
• Thus, for changing a photo diode’s conductivity, the incident radiation’s minimum energy must be equal to the material’s band gap.

In other terms,

Gap of band = Incident radiation’s energy  

⇒E = hcλ

⇒E = 1242 eV - nm620 nm = 2.0 eV .