Question

(a) In the following diagram 'S' is a semiconductor. Would you increase or decrease the value of R to keep the reading of the ammeter A constant when S is heated ?
Give reason for your answer.
(b) Draw the circuit of a photodiode and explain its working. Draw its I- V characteristics.

Answer 1

Working : In photodiode an electric field exists across the junction from n-side to p-side. When visible light with energy $h\nu$ greater than the energy gap $E_g$ illuminates the junction, then electron -hole pairs are generated in the depletion layer. Due to electric field, electrons move towards n side and holes move towards p-side,thus, giving rise to an emf.