Cross-sectional imaging and spectroscopy of GaAs doping superlattices by scanning tunneling microscopy

The scanning tunneling microscope is used to image GaAs pn-doping superlattices, cleaved in ultrahigh vacuum. Current-voltage (I-V) measurements provide a detailed view of the variation in Fermi-level position across the superlattice. The I-V curves show the clear signature of nondepleted n- and p-type material, with depleted regions appearing at the interfaces between n- and p-type layers. The number of states available for tunneling is found to provide the major source of contrast in the images.