Characterization of minority-carrier parameters is a primary interest for a range of devices, including solar cells. For on-line testing needs, contactless techniques are mandatory, as any diagnostic requiring contact formation is impractical. Here, we will describe the resonance-coupled photoconductive decay (RCPCD) technique that has proven to be a valuable diagnostic for a number of semiconductor technologies. This technique avoids some of the inherent limitations of microwave reflection. Our system is a pump-probe technique, using an optical pump and a microwave probe (400 to 900 MHz). These low frequency microwaves penetrate most silicon wafers with common doping levels. By varying the optical excitation wavelength, one can probe wafers of standard (300 to 400 mm) wafer thickness. Also, the method is very linear in sample photoconductivity, and we have observed a linear response over more than three orders of magnitude of excess carrier concentration. This attribute allows us to measure the carrier recombination lifetime over many decades of injection level, allowing the use of a procedure that is called injection-level spectroscopy (ILS).
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