FM demodulated Kelvin probe force microscopy for surface photovoltage tracking

The surface photovoltage (SPV) of a structured semiconductor surface is deduced via detection of the contact potential difference measured with Kelvin probe force microscopy (KPFM). Our setup is based on a quantitative KPFM method complemented with modulated laser illumination in order to measure SPV. A high lateral resolution and quantitative values for the SPV are obtained by operating the KPFM in the so-called frequency modulation (FM) mode which is advantageous compared to the amplitude sensitive (AM) mode as proven by our simulations. In contrast to similar studies based on scanning tunnelling microscopy, KPFM offers the clear advantage that there is virtually no electric DC field between tip and sample and, therefore, the SPV is not affected by the presence of the tip.