Theory of Operation

A semiconductor surface covered by native oxide is typically in depletion conditions regardless of its type. As a consequence the polarity of the surface barrier is characteristic of the conductivity type of the sample under test. Surface barrier polarity can be detected in a non-contact way by measuring the surface photovoltage. During such a measurement a chopped laser light is applied: by the high intensity illumination excess carriers are generated and their presence decreases the surface barrier, i.e. flatband condition is approached. The barrier change due to the illumination is detected by a probe capacitively coupled to the surface. Conductivity type is determined by the polarity of the surface barrier change due to illumination.