Frequency modulated microwave photoconductivity measurements for characterization of silicon wafers

Abstract

Frequency resolved photoconductivity measurements in the microwave frequency range are presented as a contactless tool for the characterization of silicon wafers and junctions. In particular for the characterization of junctions the change of excess carrier kinetics as a function of the injection level is important. In contrast to previous approaches the special design of the setup allows us to determine the absolute injection level experimentally from the value of the modulated microwave reflection amplitude. The method is demonstrated by measuring the ambipolar diffusion constant as a function of the excess charge carrier density of n- and p-type silicon wafers. The conditions to obtain the volume lifetime from the measurements are discussed in view of relevant experimental data. The results are promising for a contactless investigation of the injection level dependent surface/interface recombination velocity.