Forward Bias
The term for the voltage used to control the thickness of the barrier is called BIAS. When the junction was formed electrons left holes as those electrons crossed the junction to form the barrier. If the bias voltage is placed negative to the N material and positive to the P material, that is called forward bias. In that case electrons are repelled back toward the junction and likewise the holes are repelled toward the junction causing The barrier to get thinner. The electrons and holes recombine at the junction. When the bias is enough to overcome the barrier potential current will flow through the junction.
Reverse Bias
On the other hand, if the bias voltage is placed negative on the P material and positive on the N material, that’s called reverse bias. In that case, the barrier just gets thicker allowing no current to pass through the junction. At some point the voltage can be increased and the resistance of the thickened barrier will breakdown allowing current can flow.
Reverse Breakdown
The nature of that breakdown is determined by the physical characteristics of the junction. The breakdown can occur by destructive or non-destructive means. The breakdown can be due to an arc which would destroy the junction or through the Avalanche, Zener, or tunnel effects which do not permanently damage the junction. A discussion of the reverse breakdown characteristics along with the terms “minority and majority “carriers are beyond the scope of this limited post.
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