Direction: Given question consists of two statements, one labeled as the 'Assertion (A)' and the other as 'Reason (R)'. You are to examine these two statements carefully and select the answers to these items using the codes given below.

Assertion (A): At microwave frequencies, PIN diode can be used as a fast switch.

Reason (R): PIN diode has very high resistance when reverse biased and very low resistances when forward biased.

In forward bias, pin diode has low resistance whereas in reverse bias it behaves like a capacitor. Due to the capacitor property, we use a pin diode as a microwave switch.

EXPLAINATION-

PIN DIODE-

The diode in which the intrinsic layer of high resistivity is sandwiched between the P and N-region of a semiconductor material such type of diode is known as the PIN diode. The high resistive layer of the intrinsic region provides the large electric field between the P and N-region

Forward Biased PIN Diode

• When the diode is kept forward biased, the charges are continuously injected into the I-region from the P and N-region.
• This reduces the forward resistance of the diode, and it behaves like a variable resistance.

Reversed Biased PIN Diode

• When the reverse voltage is applied across the diode, the width of the depletion region increase.
• In reverse bias, the diode behaves like a capacitor. 
• The P and N region acts as the positive and negative plates of the capacitor, and the intrinsic region is the insulator between the plates.
• Due to capacitance, these diodes are used in the RF and also for microwave switches and microwave variable attenuators.