Tip geometry effects in scanning capacitance microscopy on GaAs Schottky and metal-oxide-semiconductor-type junctions

In this work, the influence of the tip geometry in scanning capacitance microscopy is investigated experimentally and theoretically on metal-oxide-semiconductor- (MOS) and Schottky-type junctions on gallium-arsenide (GaAs). Using a two-dimensional model we find that on Schottky-type junctions the electric field around the tip is screened by the surface states and that the essential parameters entering the capacitance versus voltage C(V) characteristics are the doping level and the contact area only. In contrast to that, the electric field from the tip penetrates into the semiconductor on a MOS-type junction, and the tip geometry effects are much larger. C(V) spectra are fitted to the experimental data and allowed a quantitative determination of doping levels, oxide thickness, and contact area without further calibration measurements.