单层WSe2/IVB族氧化物界面的局域晶格结构、稳定性和电子性质

The deposition of a high-k dielectric on top of the 2-Dimentional channel of WSe2 can improve the mobility of WSe2 monolayer Field Effect Transistor (FET). However, very few theoretical studies based on the properties of interdaces of WSe2 monolayer and high-k oxides which are relevant to the performance of WSe2 monolayer FET have been performed. In this proposal, we perform a systematic investigation of the local structures, stability and electronic properties of WSe2/group-IVB oxides (HfO2, ZrO2 and TiO2) interfaces by means of standard density functional theory (DFT) and hybrid DFT calculations. For local structures of the interfaces, the lattice direction match, lattice constant mismatch, relaxation and bonding characteristics of the atoms in the interfacial sites are the main focus. For electronic properties, the band offsets, density of states and the carrier mobility of the interfaces will be calculated. The effects of oxygen contain and hydrogen impurities on the structures and electronic properties of the interfaces will be studied. The goal of this proposal is to identify the relationship among the local structures of the interfaces, the electronic properties of the interfaces and the performance of WSe2 FET and thus reveal the mechanisms of the improved mobility induced by the top-gated high-k dielectrics by the comparison of the different structures and electronic properties of the interfaces considered. We will develop a rational basis to enhance the performance of WSe2 FET and thus provide theoretical guideline on design of optimal new top-gated high-k dielectrics in laboratory and industry.

改善WSe2场效应管性能的有效措施之一是在沟道材料WSe2单层上制备一层高介电常数的顶栅介质以提高其电子迁移率，与WSe2单层场效应管性能相关的WSe2单层与高介电常数氧化物所形成界面的性质目前尚缺乏有力的理论分析。本申请拟采用基于常规密度泛函与杂化密度泛函的第一性原理计算方法深入、系统地研究WSe2与IVB族氧化物（HfO2、ZrO2和TiO2）所形成界面的局域晶格结构（晶相匹配、晶格失配、原子驰豫、键长、键角等）、热力学稳定性、电子性质（能带偏移、能态密度、载流子迁移率等）及界面处氧含量和含H杂质对WSe2/IVB族氧化物界面结构和电子性质的影响规律；分析原子和电子两种结构层次上的计算数据，深入理解界面处局域结构-界面电子性质-WSe2场效应管性能三者间的依赖关系，揭示高介电常数介质提高WSe2场效应管迁移率的机制，为优选顶栅介质材料、确定介质薄膜制备工艺参数提供参考。

为研究高介电常数顶栅介质提高WSe2场效应管电子迁移率的机制，我们采用基于密度泛函的第一性原理计算方法深入、系统地研究了WSe2与IVB族氧化物（HfO2、ZrO2和TiO2）所形成界面的局域晶格结构、热力学稳定性、电子性质及界面处氧空位、H杂质和OH杂质对界面结构和电子性质的影响规律。我们的研究结果表明，HfO2/WSe2界面中氧化物与WSe2单层之间的距离最小，电荷转移最大，形成能最低，是最稳定的界面，并且HfO2表面与WSe2单层之间较强的电荷转移能帮助提高WSe2单层的迁移率，因此是用于WSe2 场效应管（FET）最适合的栅介质材料。界面处的氧空位导致界面在禁带范围产生了缺陷态，且费米能级向导带底偏移，这说明O空位相当于电子掺杂（n-型掺杂）。WSe2/IVB族氧化物界面的费米能级由于H杂质的存在而向导带底偏移了，H杂质引起了n-型掺杂，这个结果跟O空位类似。而界面的费米能级由于OH杂质的存在而向价带顶偏移了，因此OH杂质引起p-型掺杂。这些缺陷和杂质的存在会影响WSe2 场效应管（FET）的性能，与已有的实验结果相吻合。