Imaging sub-surface dopant and free electron distributions using scanning tunnelling microscopy

The interaction between sub-surface charge and the physics of the tunnelling process has been studied for a number of doped semiconductor structures. The work was carried out using a UHV STM and measurements were made in two dimensions on (110) surfaces cleaved in UHV. It is clear that for such surfaces, tunnelling spectra, and hence the tip movement traditionally used to generate topology images, depend on the sub-surface depletion beneath the tip. The influence of the semiconductor screening properties and its impact on dopant related image-formation is discussed.