Internal laser probing: A theoretical study of wave propagation effects and the physical limits of measurement accuracy

Abstract

The transient distribution of charge carriers and temperature in semiconductors has become accessible to experiments by internal laser probing techniques that exploit the electro-optical and the thermo-optical effect. In this article, two representative methods, namely free carrier absorption and laser deflection measurements, are theoretically investigated. The study makes use of analytical calculations and the recently introduced concept of virtual experiments, which is based on a physically rigorous simulation of the entire measurement process. Wave propagation phenomena and parasitic effects introduced by preparing the sample or performing the actual measurement are thoroughly analyzed to identify major sources of error and to reveal the theoretical limits of measurement accuracy and resolution. We derive a consistent evaluation rule for extracting carrier and temperature gradients from the detector signals of deflection measurements. It is quantitatively demonstrated how to optimize the setup with respect to a desired purpose, e.g., a large measurement range or a large sensitivity.