Editing Power semiconductor device (section)

===Diodes===

An ideal [[diode]] should have the following characteristics:
* When ''forward-biased'', the voltage across the end terminals of the diode should be zero, no matter the current that flows through it (on-state).
* When ''reverse-biased'', the leakage current should be zero, no matter the voltage (off-state).
* The transition (or commutation) between the on-state and the off-state should be instantaneous.
In reality, the design of a diode is a trade-off between performance in on-state, off-state, and commutation. Indeed, the same area of the device must sustain the blocking voltage in the off-state and allow current flow in the on-state; as the requirements for the two states are completely opposite, a diode has to be either optimised for one of them, or time must be allowed to switch from one state to the other (i.e., the commutation speed must be reduced).

These trade-offs are the same for all power devices; for instance, a [[Schottky diode]] has excellent switching speed and on-state performance, but a high level of leakage current in the off-state. On the other hand, a [[PIN diode]] is commercially available in different commutation speeds (what are called "fast" and "ultrafast" rectifiers), but any increase in speed is necessarily associated with a lower performance in the on-state.