Investigation of the electronic structural and optical properties of CH3NH3HgI3 crystal.

Based on the first-principles density functional theory, the electronic structure and optical properties of CH3NH3HgI3 crystal were investigated by means of generalized gradient approximation (GGA + U) approach. Then, CH3NH3HgI3 crystal was grown successfully by anti-solvent method, and the UV-vis-NIR spectra of crystal grown were investigated. The results indicate that CH3NH3HgI3 belongs to direct band-gap semiconductor with 2.801 eV of band-gap. The energy level of electrons at the top of the valence band and the bottom of the conduction band is mainly formed by Hg and I, while C, N, and H of CH3NH3+ do not participate in forming the electron configuration near the Fermi level. CH3NH3HgI3 was combined by electrostatic interactions with CH3NH3+ and [HgI4]2-. Their electrostatic interactions lead to distortion of [HgI4]2- tetrahedron and cause the increase of band-gap of CH3NH3HgI3. Moreover, steric hindrance effect of CH3NH3+ spurs [HgI4]2- tetrahedron to form 1D chain structure. The result obtained from the UV-vis-NIR spectra of crystal shows that the band-gap of CH3NH3HgI3 crystal is 2.877 eV, which is good coincident with the calculated gap (2.801 eV). Our discussions on the electronic structural and energy band of crystal suggest that CH3NH3HgI3 can be used as an ultraviolet detector material.