All material properties are calculated in the cell center and used for the
whole cell volume. Vertical position of cell centers is defined by the info
in the 'Project Configuration' window.

For instance, for the p-layer with thickness of 0.1665 and NA=3 the cell
centers will be located at z={0.02775,0.08325,0.13875}. So, the piecewise
dependence of the acceptor concentration you have set up will have no effect
(i.e. for all cells the value of 7e18 will be used). No matter you have used
scripts or piecewise approximations.

Also, script for the donor concentration will give the bottom layer of cells
with Nd=0, and two layers of cells with Nd=5e18. Thin upper layer with
Nd=6e17 will be ignored.

So, one has to be careful with z-dependent materials properties. It is a
good idea to write scripts depending on the layer thickness and number of
cells (they are globally defined parameters which are updated automatically
than the user changes settings in the 'Project Configuration' window).