Measurement of free carrier transport near semiconductor surface by terahertz time-domain spectroscopy

In recent years, wide bandgap semiconductor devices have attracted much attention. For the establishment of device processing technologies, it is crucial to characterize the carrier transport, especially occurring in a thin layer near the surface. In this study, using Si as an example, we confirmed the ability to measure such carrier transport theoretically and experimentally by terahertz time-domain spectroscopic ellipsometry (THz-TDSE). In low frequency, the conductance can be determined almost uniquely, but the separation of carrier density (N
c
) and mobility (µ) remains challenging. We propose a simple method to detect N
c
and µ of semiconductors with the same DC conductivity (σ).