Electronic and optical properties of wide band gap Tl3TaS4: A promising surface acoustic wave material

We report the effect of different approaches based on density functional theory (DFT) on first principles calculations of mechanical, electronic, and optical properties of ternary thallium tantalum sulfide, Tl3TaS4, a prospective semiconductor for application in surface acoustic wave devices. The present findings indicate that the best fit with experimental data is achieved when the DFT band-structure calculations are performed employing modified Becke-Johnson (mBJ) functional and including also in the consideration the Hubbard parameter U and spin-orbital effect (so-called mBJ+U+SO method). In particular, the application of the mBJ+U+SO method allows achieving an indirect band gap of 2.842 eV, which is close to that measured experimentally for Tl3TaS4. The calculations indicate that the valence band maximum of Tl3TaS4 is dominated by hybridized S-3p and Tl-6s states, while unoccupied hybridized S-3p and Ta-5d states yield the principal contributions to the conduction band minimum. With respect to the occupation of the valence and conduction bands by S-3p states, the present theoretical results are found to be in excellent agreement with experimental X-ray emission and absorption spectroscopy measurements of Tl3TaS4. The main optical constants have been calculated within mBJ+U+SO method revealing big perspective of application of the of Tl3TaS4 compound in optoelectronic devices.