Answer the following, giving reason:
(a) The resistance of a p-n junction is low when it is forward biased and is high when it is reversed biased.
(b) Doping of intrinsic semiconductors is a necessity for making electronic devices.
(c) Photodiodes are operated in reverse bias.

(a) Forwarding current increases significantly when the forwarding voltage across the p-n junction is just
slightly increased. Because of this, a forward biased p-n junction has low resistance (=voltage/current).
Reverse current increases little as the reverse voltage across the p-n junction increases significantly.
As a result, the p-n junction has a high resistance when reverse biased and low resistance in forward bias.
(b) Doping semiconductors produces either an excess or a shortage of valence electrons. Doping enables scientists to take use of the characteristics of collections of elements, known as dopants, in order to
modify a semiconductor's conductivity.
(c) To work in the photoconductive mode, the photodiode is reverse biased. The depletion layer becomes wider when the photodiode is biased in reverse. As a result, the junction capacitance and the response
time are reduced. The photodiode reacts more quickly as a result of the reverse bias.