Quantification of point and line defects in Si_0.6Ge_0.4 alloys with thickness variation via optical pump-THz probe measurement

Measuring defect density through non-contact, non-destructive methods without any additional sample processing has been of great interest in both academia and industry. In this study, we propose a new method to quantify the point and line defect densities of Si_0.6Ge_0.4 films by using the recombination time of the photoexcited carrier, as well as the optical pump THz probe method (OPTP). The change in the crystallinity of Si_0.6Ge_0.4 obtained from various measurements was consistent with the recombination time of the point- and line-defect states in OPTP, which changed from 107 ps to 172 ps and from 3961 ps to 870 ps, respectively. The actual defect density of each sample was extracted from photoinduced current transient spectroscopy (PICTS) for comparison with the recombination time. In addition, the non-Drude behavior of the photoexcited carrier was analyzed using two-dimensional terahertz time-domain spectroscopy (2D-TDS), which corresponds with previous measurement tools. The quantification methodology proposed in this study is expected to be advantageous to both academia and industry, as it will enable fast and accurate analysis of defects without requiring further sample processing.