A detailed theory was proposed for the scanning tunnelling microscopy of point defects which were located near to semiconductor surfaces. The conditions were derived which were required in order to get a permanent current through the gap states of a defect, and general rules were also deduced for the current spectroscopy of defects with one or two ionization levels in the gap. It was shown that these ionization levels could be completely invisible to scanning tunnelling microscopy. In the particular case of low-temperature grown GaAs which contained a high density of As-related defects, it was shown that the observation of gap states was related to the conductivity of the material due to thermally activated hopping between defects. It was proposed that scanning tunnelling microscopy should be used to measure the rates of capture and emission of carriers by surface defects.

Theory of Scanning Tunnelling Microscopy of Defects on Semiconductor Surfaces X.De la Broïse, C.Delerue, M.Lannoo, B.Grandidier, D.Stiévenard: Physical Review B, 2000, 61[3], 2138-45