Amorphous hydrogenated silicon (a-Si:H) based pn-doping superlattices grown by radio-frequency-plasma deposition onto crystalline Si substrates were cleaved in air according to the crystallographic orientation of the substrate material. Their cross-sectional face is investigated using scanning tunneling microscopy (STM) and scanning force microscopy (SFM). With constant current STM in i dry nitrogen ambient at atmospheric pressure tip deflections due to the pn-superlattice periodicity are observed. With contact mode SFM in air only the transition from the substrate to the superlattice thin film but no periodic structure is resolved. A model calculation suggests that the apparent periodic height variation in constant current STM is due to a difference between p- and n-type doped layers in their density of accessible states for tunneling.