# How deep does the depletion region in power diode penetrate the lightly doped n- layer under no bias?

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).