A new lifetime diagnostic system for photovoltaic materials

We have developed a new minority-carrier lifetime measurement apparatus for measuring the recombination lifetime in semiconductors. We describe the technique as transmission modulated photoconductive decay (TMPCD). This is a contactless, non-invasive technique that produces transient photoconductive lifetime data. The measurement procedure is very sensitive to small signals and has a superior time response for measurement of short carrier lifetimes. This technology has several advantages over resonant coupled photoconductive decay (RCPCD) and transient microwave reflection photoconductive decay (μPCD). The response time advantage provides a capability to measure very short lifetimes in thin film materials, such as nanocrystalline silicon films and nanowire composites. This is accomplished while maintaining a sensitivity that is at least comparable to RCPCD. The new technique has been successfully applied to silicon wafers, compound semiconductor thin films, nano-crystalline silicon films, and II–VI nanowires.