The microwave photoconductive decay (μ-PCD) and the surface photo voltage (SPV) techniques are proved to be powerful methods in the qualification of semiconductor bulk materials. They are applied best for standard wafers with homogeneous material quality. However, both methods have their limitations when measuring epitaxial layer (epi) wafers or silicon on insulator (SOI) structures. In its conventional realization the SPV measurement is limited by the active layer thickness. On the other hand an epi layer grown on highly doped substrate typically does not generate high enough signal in a μ-PCD measurement.
