A method and system for identifying a defect or contamination on the surface of a semiconductor or in a semiconductor. The method and system involves providing a semiconductor with a surface, such as a semiconductor wafer, providing a non-vibrating contact potential difference sensor, providing a source of illumination with controllable intensity or distribution of wavelengths, using the illumination source to provide controlled illumination of the surface of the wafer under or near the non-vibrating contact potential sensor probe tip, using the non-vibrating contact potential difference sensor to scan the wafer surface during controlled illumination, generating data representative of changes in contact potential difference across the wafer surface, and processing that data to identify a pattern characteristic of a defect or contamination.