Impact of band gap narrowing and surface recombination on photoelectrothermal modulated optical reflectance power curves

Photomodulated optical reflectance is a well established technique for surface and near surface characterizations. In this work, the nonlinear behavior of the differential reflectance as a function of the pump irradiance (104–106W∕cm2) is studied on uniformly and nonuniformly (p-n∕p+-p junctions) doped silicon structures, with a particular emphasis on the impact of band gap narrowing (BGN) and of surface recombination velocities (SRVs). We show that the BGN induced by the presence of excess carriers substantially influences the excess carrier profile. We also explain the unexpected shape of power curves on lowly doped substrate by a time-dependent variation of the SRVs during illumination.