Simultaneous charge carrier density mapping of SiC epilayers and substrates with terahertz time-domain spectroscopy

With the growing demand for efficient power electronics, SiC-based devices are progressively becoming more relevant. In contrast to established methods such as the mercury capacitance-voltage technique, terahertz spectroscopy promises a contactless characterization. In this work, we simultaneously determine the charge carrier density of SiC epilayers and their substrates in a single measurement in a doping range spanning almost three orders of magnitude, from about 8×10¹⁵ cm^-3 to 4×10¹⁸ cm^-3, using time-domain spectroscopy in a reflection geometry. Furthermore, inhomogeneities in the samples are detected by mapping the determined charge carrier densities over the whole wafer. Additional theoretical calculations confirm these results, take into account the effects of systematic material parameter uncertainties, and provide thickness-dependent information on the doping range of 4H-SiC, in which terahertz time-domain spectroscopy is capable of determining the charge carrier density.