Proposition of new stable rare-earth ternary semiconductor sulfides of type LaTlS2 (La= Er, Eu, Tb): Ab-initio study and prospects for optoelectronic, spintronic and thermoelectric applications

Based on ab-initio calculations in the framework of the density functional theory (DFT), an analysis of the structural, magnetic, thermoelectric, and optoelectronic properties of three newly designed ternary semiconductor sulfides: LaTlS2 (La = Er, Eu, Tb) is carried out. It has been established that these compounds are thermodynamically and mechanically stable. Indirect bandgaps are found with the values 1.53, 1.62, 1.70 eV for the spin up (& UARR;) channel for ErTlS2, EuTlS2, TbTlS2, respectively. For the spin down (& DARR;) channel, the obtained values are slightly lower. The paramagnetic magnetic moments are predicted by observing different band shapes in the energy band structures for the spin up (& UARR;) and spin down (& DARR;) states. The values of the magnetic moments for ErTlS2, EuTlS2 and TbTlS2 are large, being respectively: 3.00, 6.00 and 6.00 mu B. The R(omega) spectra show a very low reflectance in the IR and visible regions, however, up to 45% of the photon reflection occurs in the UV region. The spectra of the Seebeck coefficient show that EuTlS2 is initially p-type semiconductor, but becomes n type semiconductor above 350 K. Whereas ErTlS2 and TbTlS2 are initially n-type semiconductors, but become p type semiconductors at temperatures higher than 100 K.