Recombination in Semiconductors

Excess carriers in semiconductors recombine either by direct recombination of electrons and holes, or through the intermediacy of recombination centers. The latter process is the one observed in silicon and germaniun. Various impurity atoms, dislocations, vacancies, and interstitials are known to act as recombination centers. The capture rates associated with these imperfections vary over a wide range depending on their state of charge. Recombination at the surfaces is described in terms of a similar model in which surface states replace the recombination centers present in the bulk. The surface recombination velocity measures the density and capture properties of these states. A given center can act as a recombination center or a trap depending on the relative magnitude of the capture cross sections for electrons and holes. This paper reviews the analytical treatments of the different processes as well as specific experimental results.