# Why do power diodes have a p+ n- n+ construction and why not p+ p- n+?

I've been learning about power diodes and how they differ from low power diodes with the addition of a lightly doped n-type layer.
This n-type layer improves the breakdown voltage rating of the device, and improves conduction in forward bias due to the high number of injected carriers from the heavily dopes regions.
Will a power diode work the same if this n- layer is replaced with a lightly doped p-type layer? If it does, why is an n- layer preferred? Or, if it doesn't, why?

• +1 Used to be almost three times hole mobility in silicon (not germanium), when I was studying this in 1980. I remember the old figures of 1300 vs 500 for silicon and 3800 vs 1800 for germanium. But measurements may have been refined since the olden days, I suppose. (Room temp of $300\:\text{K}$.) – jonk Sep 18 '18 at 12:01