ABSTRACT
A new approach in the electric field modulation spectroscopy is presented which effectively extracts a selective photoreflectance (PR) response from a certain layer within a thin multilayer structure. This technique, which we call differential photoreflectance (DPR) spectroscopy, is based on two oppositely phased modulations from two lasers with different wavelengths, so that modulation has a gradient with respect to the depth in the sample. The application of this technique is demonstrated for a two dimensional electron gas in a high electron mobility transistor (HEMT) structure.
