Electronic structure and optical properties of Cs2HgI4: Experimental study and band-structure DFT calculations

• High-quality Cs2HgI4 single crystal has been grown by the Bridgman–Stockbarger method.
• Electronic structure of Cs2HgI4 single crystal is studied by XPS.
• First-principles calculations of total and partial densities of states are reported.
• Light absorption coefficient and specific electrical conductivity are measured.
• Main optical characteristics of Cs2HgI4 are calculated.

High-quality single crystal of cesium mercury tetraiodide, Cs2HgI4, has been synthesized by the vertical Bridgman–Stockbarger method and its crystal structure has been refined. In addition, electronic structure and optical properties of Cs2HgI4 have been studied. For the crystal under study, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces have been measured. The present X-ray photoelectron spectroscopy (XPS) results indicate that the Cs2HgI4 single crystal surface is very sensitive with respect to Ar+ ion-irradiation. In particular, Ar+ bombardment of the single crystal surface alters the elemental stoichiometry of the Cs2HgI4 surface. To elucidate peculiarities of the energy distribution of the electronic states within the valence-band and conduction-band regions of the Cs2HgI4 compound, we have performed first-principles band-structure calculations based on density functional theory (DFT) as incorporated in the WIEN2k package. Total and partial densities of states for Cs2HgI4 have been calculated. The DFT calculations reveal that the I p states make the major contributions in the upper portion of the valence band, while the Hg d, Cs p and I s states are the dominant contributors in its lower portion. Temperature dependence of the light absorption coefficient and specific electrical conductivity has been explored for Cs2HgI4 in the temperature range of 77–300 K. Main optical characteristics of the Cs2HgI4 compound have been elucidated by the first-principles calculations.

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