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Electronic structure and optical properties of Ag2HgSnSe4: First-principles DFT calculations and X-ray spectroscopy studies 


Tuan V. Vu, A.A. Lavrentyev, B.V. Gabrelian, O.V. Parasyuk, V.A. Ocheretova, O.Y. Khyzhun

Source title: 
Journal of Alloys and Compounds, 732: 372-384, 2018 (ISI)
Academic year of acceptance: 

Complex study of the electronic structure of the Ag2HgSnSe4 compound employing both experimental and theoretical methods was carried out in the present work. In particular, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+ ion-irradiated surfaces of Ag2HgSnSe4 single crystal have been measured. The present X-ray photoelectron spectroscopy (XPS) results indicate that Ag2HgSnSe4 single crystal surface is sensitive with respect to Ar+ ion-irradiation. Particularly, Ar+ ion bombardment of the single crystal surface causes significant modification in topmost surface layers resulting in abrupt decreasing the content of Hg atoms in the layers. The X-ray emission band representing the energy distribution of the Se 4p states was measured and compared with the XPS valence-band spectrum provided that a common energy scale is used. Results of such comparison reveal that the main contributions of the Se 4p states occur at the top and in the upper portion of the valence band. The experimental findings were confirmed by first-principles band-structure calculations performed in the present work employing the augmented plane wave+local orbitals (APW+lo) method as realized in the WIEN2k package. The calculations indicate that the Hg 5d and Ag 4d states are the principal contributors to the bottom and the central part of the Ag2HgSnSe4 valence band, respectively, while its upper part is dominated by contributions of the Se 4p states. Regarding the occupancy of the conduction band, the present APW+lo calculations manifest that its bottom is dominated by the unoccupied Sn 5s states. The principal optical characteristics of Ag2HgSnSe4 are elucidated by the calculations.