You are viewing a single comment's thread from:
RE: Electrical Components Basics: The Standard Diode
I never fully got around the theory of the PN junction at school. But if I remember when you apply voltage in the opposite direction it creates a bigger "depletion" area at the junction that opposes the flow of current. Is that how it works?
Yeah, that sounds about right. A properly aligned electric field can push charges through the central region but reverse bias will just increase the depletion region and make it even more difficult to conduct current. The way I understand it, the depletion region is sort of like a "neutral" region without the charge carriers.
Unfortunately my last solid state physics course stopped just short of detailed PN junction explanation, so I can't go much more into the details/math/chemistry.
I can't remember the details myself, or where I read it, but just did a quick refresher. Essentially the N-type side is doped with an impurity that provides an excess of free electrons, whilst the P-type doped to provide an excess of "holes" . An example dopant for N-type is Phosphorus which has 5 electrons in its outer shell, while P-Type might use Boron which has 3 electrons (silicon having 4 outer shell electrons).
At the PN junction, free electrons pass into the P side to fill the holes but in doing so leave a resultant charge at the junction which creates a small depletion area (visible as 0.6-0.7V forward bias voltage) . Driving it the junction in reverse bias expands the depletion region as you stated to resist current flow.
Whoever, thought this stuff up was seriously smart!