What actually happens inside a p–n junction the moment you forward-bias it?
At rest, a depletion region with a built-in barrier stops most carriers crossing.
At rest, a depletion region with a built-in barrier stops most carriers crossing. Forward bias (p to +, n to −) pushes electrons and holes toward the junction, narrowing the depletion region and lowering the barrier, so once you exceed the knee voltage (~0.7 V for silicon) current flows freely. Reverse bias does the opposite — it widens the depletion region and the diode blocks current.
Key point
Forward bias narrows the depletion region and lowers the barrier, so current flows.
Common mistake
thinking current rises smoothly from 0 V in forward bias.
Memory tip
nothing much flows until you pass the ~0.7 V knee (silicon).
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