Effect of photocarriers on acoustic wave propagation for measuring excess carrier density and lifetimes in silicon

Abstract
A new technique is described to measure temporal periodic fluctuations in the free-carrier density of silicon. It is based on the electronic dependence of the elastic constants, and involves the measurement of the perturbation in phase of an acoustic wave propagating through a region of modulated carrier density. An experiment is described in which the bulk lifetime of photogenerated carriers is determined using this technique. A theory is developed to predict the acoustic phase perturbation, and is found to agree well with experiment.