IGBT Modules - Technologies, Driver and Application (Second Edition) - page 166

Special adaptations of the inner structure and the doping concentration show successful
first signs as they have already been detailed in various publications
, and
. It will be some time yet until mass production, however.
Fig. 3.37
1.2kV IGBT with self-limiting collector-emitter voltage at the level of the
nominal static breakdown voltage
Just as with IGBTs, with diodes too – here particularly the freewheeling diodes – it can
come to an avalanche break-over. During the turn-off of the freewheeling diode a
significant proportion of the reverse recovery current still flows despite the fact that the
diode is already building up blocking voltage. This current flows in the space-charge
region of the diode as a hole current in the direction of the p-doped area (anode). The
carrier concentration p through this hole current adds to the base doping N
of the n
drift zone and reduces its blocking capability according t
The effective doping
is increased to:
p N N
D eff ,D
+ =
Eq. 3.33
A dynamic avalanche breakdown occurs (as opposed to a static break-over in the diode
blocking mode) below the actual diode blocking voltage. This can happen the sooner
the faster the associated IGBT in the commutation path turns on and forces high rates
of change of the commutating current. This effect is partially compensated, however.
During the avalanche breakdown the generated electrons (which are generated in equal
numbers as the holes) at the pn-junction drift to the n-region (cathode) and recombine
there with parts of the original hole current. The destruction of the diodemay still occur,
however, if a breakdown of the secondorder takes place (chapte
A robust diode is characterised thus by being able to survive unharmed an avalanche
breakdown at high commutation slopes and highDC-bus voltages at the same time.
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