Tauc plot


A Tauc plot is used to determine the optical bandgap, or Tauc gap, in semiconductors. The Tauc gap is often used to characterize practical optical properties of amorphous materials.
Jan Tauc showed that the optical absorption spectrum of amorphous germanium resembles the spectrum of the indirect transitions in crystalline germanium, and proposed an extrapolation to find the optical gap of these crystalline-like states. Typically, a Tauc plot shows the quantity on the abscissa and the quantity on the ordinate, where is the absorption coefficient of the material. The value of the exponent denotes the nature of the transition:
The resulting plot has a distinct linear regime which denotes the onset of absorption. Thus, extrapolating this linear region to the abscissa yields the energy of the optical band gap of the material.