Geometry effects and frequency dependence in scanning capacitance microscopy on GaAs Schottky and metal–oxide–semiconductor-Type junctions

In this work, the influence of the tip-geometry and an unusual low frequency behavior 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. On a MOS-type junction, the electric field from the tip penetrates into the semiconductor 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 moreover calibration measurements. Furthermore, we show that the natural surface depletion field on GaAs generates a permanent minority carrier accumulation around the tip–apex. In contrast to thermally generated minority carriers in the space charge region of a large area device, the minority carrier distribution around the SCM tip–apex is detected up to much higher excitation frequencies. An analytic approach to estimate the transition frequency between the low and high frequency regime is also given.