Copper(I) iodide (CuI) is the leading inorganic -type transparent conductor, attracting major attention for its promising optoelectronic properties and facile growth methods, although, commercial uptake is limited due to its as-of-yet insufficient electrical conductivity. Doping CuI with the chalcogens (O, S, Se, Te) is a viable route to tune its electrical conductivity for applications such as in thin film transistors, hole transport layers in solar cells, and transparent thermoelectric generators. The heaviest chalcogen element, Te, is yet to be explored in heavily intrinsically -type doped CuI at non-alloying concentrations, the subject of the present work. We report the effects of tellurium at the boundary between the doping and alloying regime (up to a maximum of 2.4 % Te) in CuI thin films and investigation the variation in the thermoelectric properties and electronic band structure of the material. Ion implanting tellurium into CuI led to a progressive reduction in the films' work functions from 4.9 eV to 4.5 eV while the ionization potential remained unchanged, measured through photoemission spectrometry. This signified a modulation of the Fermi energy relative to the valence band edge, having a major effect on the materials' electrical conductivity and Seebeck coefficient, the former decreasing by 3 orders of magnitude, while the latter increased by 80 %. We conducted density functional theory (DFT) calculations to elucidate the effect of tellurium doping on the band structure of CuI. Tellurium doping corroborated the shift of Fermi energy, the incorporation of impurity acceptor states deeper into the band gap, in addition to disordering the valence band maximum. This work shows that, the Fermi energy in heavily -type doped CuI can be moved away from the valence band through Te doping in addition to introducing band disorder, useful for controlling the hosts’ transport properties.

中文翻译：

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热电碘化铜（I）掺杂碲调节费米能量


碘化铜（I）（CuI）是领先的无机型透明导体，因其有前途的光电特性和简便的生长方法而引起了人们的广泛关注，但由于其导电性尚不足，商业应用受到限制。用硫属元素（O、S、Se、Te）掺杂 CuI 是调整其电导率的可行途径，适用于薄膜晶体管、太阳能电池中的空穴传输层和透明热电发电机等应用。最重的硫族元素 Te 尚未在非合金浓度的重度本征型掺杂 CuI 中进行探索，这也是本工作的主题。我们报告了碲在 CuI 薄膜中掺杂和合金化状态（最高 2.4% Te）之间边界的影响，并研究了材料热电性能和电子能带结构的变化。通过光电发射光谱法测量，将碲离子注入 CuI 导致薄膜的功函数从 4.9 eV 逐渐降低至 4.5 eV，而电离势保持不变。这意味着费米能相对于价带边缘的调制，对材料的电导率和塞贝克系数产生重大影响，前者降低了3个数量级，而后者则增加了80%。我们进行了密度泛函理论 (DFT) 计算，以阐明碲掺杂对 CuI 能带结构的影响。碲掺杂除了扰乱价带最大值之外，还证实了费米能级的变化、杂质受主态更深地融入带隙。 这项工作表明，除了引入能带无序之外，重掺杂 CuI 中的费米能还可以通过 Te 掺杂从价带移开，从而有助于控制主体的输运特性。