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Electronic and optical properties of quaternary sulfide Tl2HgSnS4, a promising optoelectronic semiconductor: A combined experimental and theoretical study


A.A. Lavrentyev, B.V. Gabrelian, Tuan V. Vu, L.N. Ananchenko, G.L. Myronchuke, O.V. Parasyuk, V.A. Tkach, K.I. Kopylova, O.Y. Khyzhun

Source title: 
Optical Materials, 92: 294-302, 2019 (ISI)
Academic year of acceptance: 

Data on coupled experimental and theoretical studies of the electronic structure and optical properties of quaternary thallium mercury tin sulfide, Tl2HgSnS4, a perspective semiconductor for application in optoelectronics, are presented in the present work. In particular, for a Tl2HgSnS4 crystal grown by Bridgman-Stockbarger technique, we have measured X-ray photoelectron (XP) core-level and valence band (VB) spectra for as-synthesized and treated with 3 keV Ar+ ions surfaces. The XP measurements reveal a substantial sensitivity of the Tl2HgSnS4crystal surface regarding treatment with Ar+ ions: such surface treatment leads to almost complete eliminating the mercury content in topmost surface layers being analyzed. Furthermore, based on computing techniques within density functional theory (DFT) framework, we have calculated the electronic band-structure of Tl2HgSnS4 through modified Becke-Johnson (mBJ) approach for exchange correlation potential involving also in computation procedure spin-orbit (SO) coupling and Hubbard parameter U (mBJ–USO technique). The present mBJ–USO calculations reveal an excellent fit of the theoretical curve of total density of states and the experimental XP VB spectrum of the Tl2HgSnS4 compound. The DFT calculations indicate that the upper portion of the XP VB spectrum of Tl2HgSnS4 is mainly due to contributions of S 3p states, the central part is formed by S 3p and Sn 5p states, the lower portion is determined from contributions of Sn 5s states, with slightly smaller input of 6s states associated with Tl and Hg atoms, while at the bottom the principal contributions come from Hg 5d5/2 and Hg 5d3/2 states. The optical absorption edge was measured for the Tl2HgSnS4 crystal and the main optical constants were calculated within mBJ–USO technique.