Using scanning capacitance microscopy (SCM), we have studied the photovoltaic effect on differential capacitance (dC/dV) signals of low-energy-BF2+-implanted silicon wafers. The surface photovoltage induced by the stray light of the atomic force microscope laser beam leads to distorted dC/dV profiles and hence perturbs the contrast of SCM images. Due to the photovoltaic effect on the junction region, the observed junction image also exhibits a narrower junction width. According to this study, the photovoltaic effect not only significantly affects the dC/dV signals but also deteriorates the accuracy of junction characterization, in particular for ultrashallow junctions and lower band-gap semiconductors. © 2003 American Institute of Physics.