Question

difference between recovery time and transit time of a diode

Answer 1

A diode operating in forward bias mode has minority carriers injected in both N and P regions. Depending on the structure of the diode, these carriers once injected will take some time to be removed. These carriers are called stored charge. The time it takes to remove the stored charge is generally referred to as recovery time. As an example (refer to the drawing): a current source is switched in and out out of a diode at T=0 and T=t1 respectively. Initially when current is switched into the diode, the voltage of the diode goes to its forward voltage quickly. When the current is removed however, the voltage stays at forward voltage for a while because of the stored minority carriers in the diode. Recovery time refers to the time it takes to clear the stored charge in the diode. In this case, the only mean of removing stored charge is by recombination. This is the same stored charge mechanism as a transistor in saturation.