A new lifetime diagnostic system for photovoltaic materials

We have developed an apparatus for measuring the minority-carrier or recombination lifetime in semiconductors. We have named the technique 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 sensitivity is comparable to that of RCPCD but considerably larger than that of μPCD. The response time advantage provides a capability to measure very short lifetimes in thin film materials, such as amorphous and nano-crystalline silicon films and nanowire composites. This is accomplished while maintaining a sensitivity that is at least comparable to RCPCD. We will show results of the application of this new technique to a wide range of photovoltaic materials. These include silicon wafers, compound semiconductor thin films, nano-crystalline silicon films, and II-VI nanowires.