Radiometric Analysis of Laser Modulated IR Properties of Semiconductors

A photothermal technique for the characterization of semiconductor materials is preseInted, in combination with the theoretical description of the signal generation process of the effects of the charge carrier density on the IR optical properties. It relies on the excitation of charge carrier density waves by modulated laser irradiation in the visible spectrum, leading to periodical variations of the IR optical properties. The detection is based on sensing the ir transmission of the semiconductor sample. The modulated laser irradiation in the visible simultaneously leads to small temperature variations and additional signal contributions due to the modulation of the iInternal IR radiation, which can be minimized and eliminated by appropriate focussing conditions. A principal understanding of the signal generation mechanism has been achieved by timedependent measurements with a gradually increasing iIntensity of the external IR radiation source, while frequency-dependent measurements of the modulated IR transmission signal provide quantitative information on the semiconductor properties.