Is it possible to build two or more kinds of doped silicon on each other? For example, building a 1 um p-doped silicon on 1um n-doped one? while they have been separated by an insulation layer?
If the insulation layer is oxide, creating such a layer-by-layer structure might be complex on a monocrystalline silicon wafer. However, employing an in-plane structure via photolithography allows for far easier realization.