Overlay plot of geometry and analytic function

Dear Comsol Users
I defined an analytical function depending on x and y which I would like to plot in overlay with my geometry for which it is defined (similarly to the plot on page 7 of the semiconductor diode example).
How do I do that?

I created a plot group of the analytical function, but I dont know how to "add" the geometry domains to this plot.
Thanks for hints or suggestions.