Nondestructive measurements of depth distribution of carrier lifetimes in 4H-SiC thick epitaxial layers using time-resolved free carrier absorption with intersectional lights.

To achieve low on-state and switching losses simultaneously in SiC bipolar devices, the depth distribution of the carrier lifetime within the voltage blocking layer and the techniques used for observing the carrier lifetime distribution are important considerations. We developed a measurement system of the time-resolved free carrier absorption with intersectional lights (IL-TRFCA) for the nondestructive measurements of the depth distribution of the carrier lifetime in 4H-SiC thick epilayers. To confirm the reliability of the measurement results, we also performed TRFCA measurements to the cross section of the samples. As a result, although the lifetimes are underestimated owing to an inevitable diffusion of the carriers from the measurement region, the system was able to observe a carrier lifetime distribution up to a depth of 250 µm. Our IL-TRFCA system demonstrated a depth resolution of ∼10 µm, which is the best resolution among previously reported nondestructive measurement techniques. We consider the proposed system to be useful for the development of SiC bipolar devices.