Narrow Bandgap in 尾-BaZn2As2 and Its Chemical Origins

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• 作者：Zewen Xiao ; Hidenori Hiramatsu ; Shigenori Ueda ; Yoshitake Toda ; Fan-Yong Ran ; Jiangang Guo ; Hechang Lei ; Satoru Matsuishi ; Hideo Hosono ; Toshio Kamiya
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：October 22, 2014
• 年：2014
• 卷：136
• 期：42
• 页码：14959-14965
• 全文大小：568K
• ISSN：1520-5126

文摘

尾-BaZn₂As₂ is known to be a p-type semiconductor with the layered crystal structure similar to that of LaZnAsO, leading to the expectation that 尾-BaZn₂As₂ and LaZnAsO have similar bandgaps; however, the bandgap of 尾-BaZn₂As₂ (previously reported value 鈭?.2 eV) is 1 order of magnitude smaller than that of LaZnAsO (1.5 eV). In this paper, the reliable bandgap value of 尾-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鈥揂s 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 nonbonding Ba 5d_x²鈥?i>y² orbitals form an unexpectedly deep conduction band minimum (CBM) in 尾-BaZn₂As₂ although the CBM of LaZnAsO is formed mainly of Zn 4s. These two origins provide a quantitative explanation for the bandgap difference between 尾-BaZn₂As₂ and LaZnAsO.