Deviation from typical I-V characteristics of a diode in high frequency
Reverse recovery time quote from Wiki: -


  Following the end of forward conduction in a p–n type diode, a reverse
  current can flow for a short time. The device does not attain its
  blocking capability until the mobile charge in the junction is
  depleted.


This is why some diodes are useless for switching circuits or power supplies or for radio frequency applications. Some versions of the 1N400x diode can have reverse recovery times of 30 us: -