Narrow Bandgap in β-BaZn₂As₂ and Its Chemical Origins

Abstract

β-BaZn2As2 is known to be a p-type semiconductor with the layered crystal structure similar to that of LaZnAsO, leading to the expectation that β-BaZn2As2 and LaZnAsO have similar bandgaps; however, the bandgap of β-BaZn2As2 (previously-reported value ~0.2 eV) is one order of magnitude smaller than that of LaZnAsO (1.5 eV). In this paper, the reliable bandgap value of β-BaZn2As2 is determined to be 0.23 eV from the intrinsic region of the temperature dependence of electrical conductivity. The origins of this narrow bandgap are discussed based on the chemical bonding nature probed by 6 keV hard X-ray photoemission spectroscopy, hybrid density functional calculations, and the ligand theory. One origin is the direct As-As hybridization between adjacent [ZnAs] layers, which leads to a secondary splitting of As 4p levels and raises the valence band maximum. The other is that the non-bonding Ba 5dx2y2 orbitals form unexpectedly deep conduction band minimum (CBM) in β-BaZn2As2 although the CBM of LaZnAsO is formed mainly of Zn 4s. These two origins provide a quantitative explanation for the bandgap difference between β-BaZn2As2 and LaZnAsO.

Ligand-Hole in [SnI6] Unit and Origin of Band Gap in Photovoltaic Perovskite Variant Cs2SnI6

“…Compared with the LDA and PBE96, the HSE06 gave better results, as it often does for semiconductors. 24 In particular, when ¡ = 34%, the HSE06 provided the lattice parameters and bonding lengths within 1.5% errors from the room-temperature experimental values and reproduced the experiment band gap value.…”

Photoemission and x-ray absorption studies of the isostructural to Fe-based superconductors diluted magnetic semiconductorBa1−xKx(Zn1−Suzuki1, Zhao2, Shibata3 et al. 2015Phys. Rev. B372180View full textAdd to dashboardCite

“…The calculations were done using the experimentally determined tetrago-nal lattice constants a = 4.12Å, c = 13.58Å 7 and the arsenic height h As = 1.541Å 15 . First we tried the local density approximation (LDA) and generalized gradient approximation (GGA) exchange functionals 16,17 , but they gave overlapping conduction and valence bands, inconsistent with the semiconducting electrical conductivity with a band gap of 0.23 eV 18 . This is the well-known underestimation of band gap in LDA and GGA, and therefore we next employed the so-called modified Becke-Johnson exchange potential (mBJ) implemented in Wien2k program 19 with a standard mixing factor for the exact-exchange term of 0.25 20 .…”

Hole doping and pressure effects on the II-II-V-based diluted magnetic semiconductor (Ba1−xKx)

“…6 (b)). Pressure induced semiconductor to metal transition in the II-II-V based Ba(Zn,Mn) 2 As 2 is connected to As-As hybridization [12], which is related to the interlayer As-As distance, d. In the compound β-BaZn 2 As 2 [37], strong As-As hybridization as a result of a relatively short d = 3.7 Å between adjacent [Zn,As] layers leads to a secondary splitting of the bonding and antibonding states of As 4p levels. The latter, formed by As 4p z states are found near the valence band maximum (VBM).…”

“…The latter, formed by As 4p z states are found near the valence band maximum (VBM). It is shown [37] that the size of the bandgap is controlled by the proximity of these states to the Fermi level, which strongly depends on the As-As spacing. With a slight decrease in d, the hybridization of As atoms becomes larger, and widens the VB.…”