Question

A p-n junction diode can be used as:
A. Amplifier
B. Detector
C. oscillator
D. Capacitor

Answer 1

Hint: A Pn junction diode is used as a photodiode
• A special case of pn junction diode is used as Zener diode
• And due to the unique character of the flow of current in only one direction, it is also used as a rectifier

Complete step by step answer:
A photodiode is a PN-junction diode that converts light energy to electric current.
When a light photon falls on the pn junction diode it gives energy to the electron present in the diode which after gaining energy from the falling photon starts moving in the depletion region it collides with atoms and thus breaking or ionizing them into holes and electrons which further repeats the process and thus flow of electric current is set up. They are also called a light detector, and a light-sensor. Photodiodes are always made to work in reverse bias condition. Typical photodiode materials are Silicon and Germanium.
Its electric symbol is

Hence, the correct answer is option (B).

Additional information:
PN Junction Diode: A PN-junction diode is formed by fusing a p-type semiconductor and an n-type semiconductor creating a potential barrier voltage across the diode junction.
Biasing of PN junction diode and this is based on the voltage applied:
Forward bias: When we connect the positive terminal of the voltage potential is connected to the p-type while the negative terminal is connected to the n-type.
Reverse bias: When we connect the negative terminal of the voltage potential is connected to the p-type and the positive is connected to the n-type.

Note:
• When a photon falls on the diode it imparts energy to its electrons which set them in motion and the flow of electric current takes place the falling photon has the same effect on the PN junction diode as an applied voltage
• When a voltage is applied to a pn junction diode the current flows only in one direction
• When voltage is applied the electrons start to move across the PN junction diode and in the depletion region the breakdown occurs due to which flow of current is established
• Due to the flow of current in one direction, only the diode is used as rectifier there will not be the negative cycle so it will convert AC into DC