Physics of imaging p-n junctions by scanning tunneling microscopy and spectroscopy

Combined voltage-dependent scanning tunneling microscopy ~STM! images with atomic resolution, local scanning tunneling spectroscopy, and simulations of the potential distribution in the interface STM tip system are used to extract the physical imaging mechanisms of GaAs p-n interfaces in STM images. It is shown that ~i! the tip-induced changes of the potential near the interface result in the tunneling characteristics of the p-type (n-type! layer being dragged into the interfaces’ depletion region at positive ~negative! sample voltage. ~ii! This leads to a considerable reduction of the apparent width of the image of the depletion zone in STM images. ~iii! At small negative sample voltages, a pronounced depression line appears. The depression is directly correlated with the electronic interface. It arises from the interplay of competing current contributions from the valence and conduction bands. This understanding of the imaging process allows us to develop methods on how to extract accurate physical data about the properties of the electronic interfaces from scanning tunneling microscopy images.