Band structure and photoconductivity of blue-green light absorbing AlTiN films
Band structure and photoconductivity of blue-green light absorbing AlTiN films
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DOI：
10.1039/c7ta03936k
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发表时间：
2017-10
影响因子：
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通讯作者：
N. Tatemizo;Y. Miura;K. Nishio;Shunsaku Hirata;Fumihiro Sawa;K. Fukui;T. Isshiki;S. Imada
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文献类型：
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作者：
N. Tatemizo;Y. Miura;K. Nishio;Shunsaku Hirata;Fumihiro Sawa;K. Fukui;T. Isshiki;S. Imada
我们研究了重钛掺杂（高达11.0%的Ti）AlN薄膜（AlTiN）的能带结构和光电导性，其光吸收起始于约2.2 eV。X射线衍射（XRD）和透射电子显微镜的结果表明，薄膜由c轴取向的纤锌矿结构。X射线吸收近边结构（XANES）和K边扩展X射线吸收精细结构（K-edge extended X-ray absorption fine structure）结果表明，Ti原子占据Al原子3+/4+混合价位。从头计算进行了使用晶格常数估计从XRD数据与Ti原子占据Al网站的超晶胞。结果表明，Ti驱动态形成在AlN的导带（CB）底部下方，并且在高Ti浓度下几乎与其合并。计算的能带结构进行了实验验证，使用X射线光电子能谱的价带（VB）区域和N K边XANES。在吸收边附近的激发能量，光电导观察到的薄膜与8.3%和11.0%的Ti，这意味着Ti驱动的状态开始形成CB在这些Ti浓度。光电子产额谱结果表明，相对于真空能级，VB的势能约为6.0 eV。结合吸收边能量，得出AlTiN是一种很有前途的太阳能转换候选材料。
We investigated the band structure and photoconductivity of heavily Ti-doped (up to 11.0% of Ti) AlN films (AlTiN) with an optical absorption starting at around 2.2 eV. X-ray diffraction (XRD) and transmission electron microscopy results revealed that the films consisted of a c-axis oriented wurtzite structure. Ti K-edge extended X-ray absorption fine structure and X-ray absorption near edge structure (XANES) results suggested that most of the Ti atoms occupied Al sites having a 3+/4+ mixed valence. Ab initio calculations were conducted using lattice constants estimated from XRD data for supercells with Ti atoms occupying Al sites. It was revealed that the Ti-driven states were formed just below the bottom of the conduction band (CB) of AlN, and almost merged with it at high Ti concentrations. The calculated band structure was experimentally verified using X-ray photoemission spectroscopy of the valence band (VB) region and N K-edge XANES. At the excitation energy near the absorption edge, photoconduction was observed for films with 8.3% and 11.0% Ti, meaning that the Ti-driven states started forming a CB at these Ti concentrations. Photoelectron yield spectroscopy results implied that the potential energy of the VB was around 6.0 eV with respect to the vacuum level. Together with the absorption edge energy, it is concluded that AlTiN is one of the promising candidate materials for solar energy conversion.