In a p-n junction under equilibrium:

The correct answer is Option (3) → No net current flows

(A) In a semiconductor diodes, carriers (electrons and holes) can indeed be generated by photo-exciation, which occurs when semiconductor is exposed to light.

(B) Yes, electron holes pair are generated as this is a basic principle of operation in photodiodes.

(D) Photodiodes can be used as photodetector as it operates by converting incident light into electrical current.

(E) The zener diode is used for voltage regulation, and its specification should be choosen based on the required output voltage.