Influence of the tip work function on scanning tunneling microscopy and spectroscopy on zinc doped GaAs

The authors investigated the influence of the tip work function on the signatures of zinc in gallium arsenide with scanning tunneling microscopy and spectroscopy. By deliberately inducing tip modifications, the authors can change the tip work function between 3.9 and 5.5 eV, which corresponds to the expected range for tungsten of 3.5-6 eV. The related change in flatband voltage has a drastic effect on both the dI/dV spectra and on the voltage where the typical triangular contrast appears in the topography images. The authors propose a model to explain the differences in the dI/dV spectra for the different tip work functions. By linking the topography images to the spectroscopy data, the authors confirm the generally believed idea that the triangles appear when tunneling into the conduction band is mainly suppressed. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3498739]