or drift region, layer with injection of holes from the (p+)
collector. The drift region supports the bulk of the depletion
region formed by the OFF-state collector voltage, but also
contributes a significant portion to the ON-state loss from the
finite drift region resistance [3]. As the IGBT voltage hold off
capacity increases, the thickness of the drift region generally
increases. Therefore, the drift region requires deeper ambipolar
diffusion lengths at high-level injection levels for a sufficient
carrier concentration across the entire drift region [2]. Highminority carrier concentration is typically present in the higher
voltage-rated IGBT drift regions during the ON-state to mitigate
the drift region resistance and forward saturation voltage. As a
result, injection and recombination of large amounts of charge
will result in slower turn-on and turn-off transitions. This is
especially evident in the decaying current tail during last portion
of the turn-off transition [4].