Enhanced Born charges in III-VII,IV-VII2, andV-VII3compounds

Abstract

We report electronic-structure and lattice dynamics calculations on selected III-VII, IV-VII 2 , and V-VII 3 compounds. The common characteristic of these largely ionic compounds is that their outmost cation-s states are fully occupied and thus the conduction-band states are derived from the more spatially extended cation-p states, resulting in significant cross-band-gap hybridization, which enhances Born effective charges substantially. The large Born charges cause large splitting between longitudinal and transverse optic phonon modes and large static dielectric constants resulting mostly from the lattice contribution. This can lead to effective screening of defects and impurities that would otherwise be strong carrier traps and recombination centers and may therefore have positive effects on the carrier transport properties in radiation detectors based on these soft-lattice halides.

Shallow halogen vacancies in halide optoelectronic materials

“…21,22,24 Large static dielectric constants (such as 30.6 for TlBr) result in very small image charge corrections, 42 which do not affect the conclusions of this paper.…”

First principles study of native defects in InI

“…The strong inter-layer bonding is evidenced by the short interlayer In-In bond length of 3.57 Å and small phonon anisotropy. 15 InI also has high density (5.3 gm/cm 3 ) and wide bandgap ($2 eV), 19,20 suitable for room-temperature radiation detection. Its low toxicity compares favorably against TlBr, HgI 2 , and PbI 2 .…”

Investigation of Bismuth Triiodide (BiI3) for Photovoltaic Applications

“…To demonstrate this approach, we investigate the potential of bismuth triiodide (BiI 3 ) as a photovoltaic absorber, through both theory and experiment. BiI 3 has a long history of study in X-ray detectors, 4-7 given its high density and high atomic number of constituent elements, few competing phases in the Bi-I system, 4 wide bandgap of 1.67 eV, 8 large static dielectric constant (albeit anisotropic), 9 and an electron mobility that has been measured as high as 260±50 cm 2 /(V·s) or 1000±200 cm 2 /(V·s) with Sb-doping. 4,10 The hole mobility is expected to be much lower due to the difference in carrier effective masses; previously we calculated the hole and electron effective masses in the BiI 3 R3 phase to be 10.39 and 1.85, respectively.…”