Narrow Bandgap in beta-BaZn2As2 and Its Chemical Origins

Abstract

Beta-BaZn2As2 is known to be a p-type semiconductor with the layered crystal structure similar to that of LaZnAsO, leading to the expectation that beta-BaZn2As2 and LaZnAsO have similar bandgaps; however, the bandgap of beta-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 beta-BaZn2As2 is determined to be 0.23 eV from the intrinsic region of the tem-perature dependence of electrical conductivity. The origins of this narrow bandgap are discussed based on the chemi-cal 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 beta-BaZn2As2 although the CBM of LaZnAsO is formed mainly of Zn 4s. These two origins provide a quantitative explanation for the bandgap difference between beta-BaZn2As2 and LaZnAsO.

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• Photoemission and X-ray Absorption Studies of the Diluted Magnetic Semiconductor Ba${}_{1-y}$K${}_y$(Zn${}_{1-x}$Mn${}_x$)${}_2$As${}_2$ Isostructural to Fe-based Superconductors
• Magnetic Properties and Electronic Configurations of Mn Ions in the Diluted Magnetic Semiconductor Ba${}_{1-x}$K${}_x$(Zn${}_{1-y}$Mn${}_y$)${}_2$As${}_2$ Studied by X-ray Magnetic Circular Dichroism and Resonant Inelastic X-ray Scattering