A PIN diode has an intrinsic (
i) layer between
p and
n layers. When reverse bias is applied depletion layers are formed at
p-i and
i-n junctions.
The effective/width of depletion layer increases by the width of i layer. It can be used as a voltage controlled attenuator.
At high frequencies the rectification effect ceases and impedance of diode is effectively that of i layer.
This impedance varies with the applied bias. It is used in high frequency switching circuits, limiters, modulators etc.
