Quantitative determination of sheet resistance of semiconducting films by microwave near-field probing

We propose and experimentally approve a method for determining the sheet resistance R-sh of a semiconducting film on a dielectric substrate from the near-field (NF) microwave measurements data. The method is based on the earlier developed theory for NF microscopy of plane layered media. The fitting parameters of the theoretical model were sought using a universal set of calibration standards, specifically, bulk-homogeneous Si slabs varying in the doping degree. Experimental investigations were assisted by a 3 GHz resonance probe with an aperture of about 1 mm. As test structures we used n-GaN films of 0.03-15 k Omega sheet resistance, grown on a sapphire substrate. The accuracy of the technique was assessed by comparing the NF probing data with the dc measurements of R-sh in the Van-der-Pauw (VDP) method. For R-sh < 4 k Omega the root-mean-square deviation of NF from VDP data is approximately equal to 20%. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4794003]