**6. Conclusion**

The low-temperature investigation convincingly demonstrates the presence of a second surface state and a wide absorbance of 1.2 eV in bismuth selenide using TRUS. While the surface state-related transition occurs at ~1.2 eV, ~1.1 eV, and ~ 1.0 eV above the Fermi surface in bismuth selenide, bismuth telluride, and antimony telluride, respectively. Thus, this work demonstrates unequivocally that temperaturedependent analysis of charge carrier and phonon dynamics aids in the extraction of surface states associated transitions within TI. Additionally, the temperature dependency of the COP mode is established in all these TIs. At 100 K, 50 K, and 5 K, the charge carrier dynamics of Bi2Te3 and Sb2Te3 show a shift from their surface state to an excited state in the conduction band, which is due to increasing carriers in the surface conduction channel. Thus, investigation of TIs at low temperatures reveals the emergence of TSS-related transitions and their dominance at low temperatures, which is repressed at room temperature due to bulk carriers' thermalization.
