Contact potential difference of Au and GaInAs by electrostatic force microscopy

For a metallic surface (Au) and highly doped (N+) and (P+) semiconductor sur faces (GaInAs) and for localised zones (2 x 2 mu m) we have measured using an electrostatic force microscope the variation of the gradient of the electrostatic force by the signal (phase of the oscillating movement of the metallised tip) as a function of the sample-tip potential difference (-4 V to +4 V). In both cases the signal shows a quadratic variation with the sample-tip potential difference. The variation of the signal is of the order of magnitude of the theoretical predictions obtained by modelling the shape of the tip by a truncated cone + a portion of a sphere. Using the parabolic curve that fits the experimental results, the value of tho contact potential difference, corresponding to a zero value of the electrostatic force gradient, can be determined with an accuracy of 50 mV. The contact potential difference, measured between the metallised tip and the metal (Au), taken as a reference, allows the work function of the metal tip to be determined (5.25 eV). The values of the contact potential difference for the GaInAs (N+) and (P+) surfaces can be explained by the Fermi level pinning due to surface charges.