Lifetime spectroscopy is a valuable tool in a number of silicon-based technologies. Currently, lifetime measurement is the most sensitive diagnositc for identification of low-level metal impurities in silicon by using the ratio of high-injection to low-injection lifetime. When a single impurity dominates recombination, the lifetime as a function of injection level provides a measure of the defect concentration. Another measurement parameter, that has not been comonly used, is the lifetime as a function of temperature. Temperature-dependent lifetime analysis leads to a better understanding of trapping-delayed recombination rates, trapping and recombination center energy levels and activation energies, temperature-dependent capture cross sections, and surface or grain boundary recombination or trapping effects. A contactless measurement technique has been develpoed that provides the sample's recombination lifetime over a temperature range from 80 K to 300 K. A sample is coupled to the measurement circuitry that is placed into a Dewar where it is cooled by liquid nitrogen. Lifetimes are then measured as the sample is allowed to warm to room temperature. Data will be shown on these variable-temperature lifetime measurements, which have been made on silicon wafer material ranging from high-quality float-zone-grown wafers to low-cost polycrystalline materials used in photovoltaics.
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