There are at least two phases to learning about electronics. In the first phase, you learn about how components are supposed to work. In the second phase, you learn about how they really work. Wires have resistance and inductance. Adjacent wires have capacitance. Capacitors leak. Inductors have resistance. All of these things matter. [Learnelectronics] has a recent video that explores recovery time for a diode — a phase two conversation.
If you haven’t run into recovery time before, it is the amount of time the diode takes to shut off after it is conducting. This manifests itself as a little undershoot where the signal that the diode should block leaks through briefly.
The video looks at a few different diode types at different frequencies. The recovery time makes a difference in several designs including switching power supplies. If you dig into the physics, there is a usually a trade-off between several other parameters and recovery time. Just to give you an idea, the datasheet for a BAT42 Schottky diode says the reverse recovery time at 10mA is no more than 5 ns.
The video shows reverse recovery time, but forward recovery time is a thing too, though that usually isn’t such a big deal until you deal with very high currents. If you want a more technical explanation, there are good application notes from Vishay and Fairchild, to read.
If you want a different take on the same subject, [w2aew] also did a video on this topic a while back.