What is the reason for the large forward voltage drop of fast recovery diodes?

When testing the fast recovery diode circuit, if there is an abnormality in the fast recovery diode, the PN junction will cause the forward voltage drop of the fast recovery diode to be too large.
The internal structure of a fast recovery diode is different from that of a regular diode, as it adds a base region I between P-type and N-type silicon materials to form a P-I-N silicon wafer. Due to the thin base region, the reverse recovery charge is very small, which not only greatly reduces the TRR value, but also reduces the transient forward voltage drop, allowing the diode to withstand high reverse operating voltages.
The reverse recovery time of a fast recovery diode is generally several hundred nanoseconds, the forward voltage drop is about 0.6V, the forward current is several amperes to several thousand amperes, and the peak reverse voltage can reach several hundred to several thousand volts. The reverse recovery charge of the ultrafast recovery diode is further reduced, allowing its TRR to be as low as tens of nanoseconds. If the measured forward voltage drop of the fast recovery diode is abnormally high, it may be due to the purchase of a PN structure diode.