Next generation of power semiconductor devices will be designed and op
timized to meet the specific application requirements. Mixed-mode simu
lations are used to study the carrier dynamics in punch-through and no
npunch-through Insulated Gate Bipolar Transistor (IGBT) structures dur
ing soft- and hard-switching conditions. The simulation results are sh
own to qualitatively predict the measured bump in the tail current wit
h varying output dv/dt conditions and excessive forward conduction vol
tage under varying di/dt conditions. A new physical effect termed ''co
nductivity modulation lag'' is shown to occur during turn-on under sof
t-switching conditions. This mechanism is caused by the fact that mino
rity carrier injection into the base of the bipolar transistor signifi
cantly lags behind the rate at which drift region conductivity can be
modulated. The proposed phenomenon leads to an inductive effect that r
esults in dynamic voltage saturation during turn-on and causes excessi
ve forward voltage drop.