beta-BaZn2As2中的窄带隙及其化学成因
Narrow Bandgap in beta-BaZn2As2 and Its Chemical Origins
摘要：
已知β-BaZn 2As 2是具有与LaZnAsO类似的层状晶体结构的p型半导体，导致预期β-BaZn 2As 2和LaZnAsO具有类似的带隙;然而，β-BaZn 2As 2的带隙（先前报道的值~0.2 eV）比LaZnAsO的带隙（1.5 eV）小一个数量级。本文从电导率温度依赖性的本征区确定了β-BaZn_2As_2的可靠带隙值为0.23eV。基于6 keV硬X射线光电子能谱、杂化密度泛函计算和配体理论探讨了这种窄带隙的起源。一个起源是相邻[ZnAs]层之间的直接As-As杂化，这导致As 4p能级的二次分裂并提高了价带最大值。另一种是虽然LaZnAsO的导带底（CBM）主要由Zn 4s形成，但在β-BaZn 2As 2中非键Ba 5dx 2-y2轨道意外地形成了深导带底（CBM）。这两个起源提供了一个定量的解释β-BaZn 2As 2和LaZnAsO之间的带隙差异。
英文摘要：
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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