The Tauc plot is a method that is widely used for the determination of band gap. Shown next is theprocedure for determining the band gap from a diffuse reflectance spectrum using the Tauc plot. Process for Obtaining Band Gap Using Tauc Plot 1. The following relational expression proposed by Tauc, Davis, and Mott is used.where h: Planck's constant, ν: frequency of vibration, α: absorption coeffi..