I could find references for describing the depletion layer in a power diode under reverse bias and the consequent classification of Non-punch through and Punch-through diodes.
But I couldn't find a satisfactory explanation of how the depletion layer looks like under no bias. How far does the depletion layer extend into the n- layer? My guess is that the depletion layer width is small in the heavily dopes p+ region and large in the lightly doped n- region (but less width than in reverse bias condition).


1 Answer 1


It is impossible to answer your question without knowing the (relative) doping levels and the width of the N region.

Usually in power diodes the n region is lightly doped and also wide to increase the reverse breakdown voltage.

At zero bias the charges in the N and P depletion regions are be the same. So if the P+ region has 2x the doping level of the N region, the P+ depletion region will be 1/2 as wide as the N depletion region.

If the N region is wide enough to contain the complete depletion region (it does not reach the N+ part) then the relative sizes of the depletion regions will match the relative doping levels.

If the N region is not wide enough to contain the complete depletion region so part of it is inside N+ region then things get more complex.


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