In a p–n junction photo cell, the value of the photo electromotive force produced by monochromatic light is proportional to: -
A
The intensity of the light falling on the cell
B
The frequency of the light falling on the cell
C
The voltage applied at the p–n junction
D
The barrier voltage at the p–n junction
The answer is A.
Solution
In a p-n junction photocell, each absorbed photon (of energy greater than the band gap) creates an electron-hole pair near the junction. The junction field separates these carriers: electrons go to the n-side and holes to the p-side, producing a photo emf and a photocurrent. For monochromatic light of a fixed frequency, the number of electron-hole pairs produced per second is proportional to the number of photons falling per second, i.e. to the intensity of the light. So the photo emf $\propto$ current through the cell, and the current $\propto$ intensity. Hence the photo emf is proportional to the intensity of the light falling on the cell.
ConceptPhoto emf and light intensity
Semiconductor Electronics: Materials, Devices and Simple Circuits in past papers
106 questions from this chapter have appeared across 24 exam years.
