  Thermal Admittance Spectroscopy (TAS) as become a popular technique to
determine trap state density and energetic position in semiconductors. In the
limit of a large number of trap states ($>10^{16} \text{cm}^{-3}$), Fermi-level
pinning undermines the assumptions used in the analysis of TAS data, which
leads to a significant underestimation of the trap state density. Here, we
develop the tools to detect and account for the occurrence of Fermi-level
pinning in TAS measurements.
