Guter Link, mit guten Antworten.
Ich sehe da im Moment zwei Effekte:
- Transitzeit von Ladungsträgern durch die Sperrschicht
- Rekombinationszeit, bis freie Elektronen die Löcher wieder aufgefüllt
haben
Bisher kannte ich nur die Transitzeit aus dem TS.
- - - -
compumike schrieb:
space charge within a P-N junction needs to be established before
forward current can flow. (If the first sentence makes you ask why,
that's really a separate question -- perhaps this can help. Let's just
look at the dynamics of establishing and neutralizing that space
charge.)
From zero, this space charge can be established quite quickly, because
an externally applied forward bias voltage can route electrons
externally around. Electrons diffuse from the n-type material into the
edge of the p-type material, holes in the p-type material diffuse into
the edge of the n-type material, and at the metal interfaces, new
electrons are injected into the n-type end and holes are generated at
the p-type end to produce free electrons that can flow in the external
circuit. All of these flows are flows of majority carriers in their
respective materials, so diffusion happens quickly driven by much larger
concentration gradients. A space charge develops rapidly because
majority carriers are flowing to turn the diode on -- electrons in the
n-type material, and holes in the p-type material.
However, if the external voltage is then reversed to be a reverse bias,
the space charge is attracted to itself to recombine. But this
recombination only happens through the diffusion of minority carriers.
This minority carrier diffusion has much smaller concentration
gradients, and therefore diffuses orders of magnitude more slowly. An
external circuit providing reverse bias can aid in speeding this
recombination, as it can allow for faster neutralization of excess holes
that migrated back to the p-type material, and removal of excess
electrons that migrated back to the n-type material. This hole-electron
recombination or charge neutralization is assumed to happen essentially
instantaneously at the semiconductor-metal interfaces, so if the
external current can supply and remove electrons under reverse bias, it
will do so much faster than the "normal" hole-electron recombination
rate in the bulk of the semiconductor. That's why there can be huge
reverse currents during the reverse recovery time.