Origin of the optical absorption of TlGaSe2 layered semiconductor in the visible range

Abstract

The results from the investigation of optical absorption in TlGaSe2 layered bulk semiconductor in the wavelength range of 400-900 nm between the temperatures of 19 K and 300 K are presented and discussed. In the results, the layered semiconductor TlGaSe2 is interpreted as a direct band gap semiconductor with a band gap of about 2.04-2.14 eV at 300 K. Additionally, the optical transmission spectrum of TlGaSe2 exhibited some peculiarities, which were attributed to indirect allowed interband transitions. It has been explained that the optical absorption edge of TlGaSe2 can be characterized by the presence of an Urbach-like tail as well as a high-energy Tauc absorption region. The Tauc slope and Tauc energy gap were extracted from the absorption coefficient data by using the Tauc procedure. The results revealed that the 'amorphized' structure of TlGaSe2 which is prominent in near conduction/valance band energy states, cannot be ignored for the understanding of the optical transition mechanisms in this semiconductor.