Fast recovery diodes are designed to provide ultra high switching speed. They are mainly classified into two :-
Diffused PN Junction Diodes
Metal Semiconductor Diodes
The total recovery time for a P-N Junction diode can be substantially reduced by introducing efficient recombination centers, such as Au and Si, to the bulk material. Although the recovery time is directly proportional to the lifetime, it is not possible to reduce recovery time to Zero by introducing an extremely large number of recombination centers, because the reverse generation current of a P-N junction is proportional to recombination centers. For direct band gap Semiconductors, such as GaAs, the minority carrier lifetimes are much smaller than that of silicon. This results in ultrahigh speed GaAs P-N junction diodes with recovery times of the order of 0.1ns or less.