超薄ZnO多晶型薄膜的限制效应：电子和光学性质
Confinement effects in ultra-thin ZnO polymorph films: electronic and optical properties
摘要：
基于广义梯度和混合第一性原理模拟，本文对ZnO超薄膜的电性质进行了全面的表征，分别沿体心四面体（010）、立方烷（100）、h-BN（0001）、闪锌矿（110）、纤锌矿（10 $\bar{1}$ 0）和（0001）取向切割。局域态密度的特性进行了分析，在马德隆势的减少欠配位原子和表面状态/共振出现在VB的顶部和底部的CB。发现薄膜中的间隙宽度大于相应块体中的间隙宽度，这归因于量子限制效应。测定了薄膜的高频介电常数分量，计算了薄膜的吸收光谱。由于从表面共振或到表面共振的过渡，它们显示出刚好高于吸收阈值的特定特征。这项研究提供了第一次了解有限的尺寸效应的ZnO薄膜的电子性质和基准，这是有望通过光谱技术促进超薄膜的实验表征。
英文摘要：
Relying on generalized-gradient and hybrid first-principles simulations, this work provides a complete characterization of the electronic properties of ZnO ultra-thin films, cut along the Body-Centered-Tetragonal(010), Cubane(100), h-BN(0001), Zinc-Blende(110), Wurtzite(10$\bar{1}$0) and (0001) orientations. The characteristics of the local densities of states are analyzed in terms of the reduction of the Madelung potential on under-coordinated atoms and surface states/resonances appearing at the top of the VB and bottom of the CB. The gap width in the films is found to be larger than in the corresponding bulks, which is assigned to quantum confinement effects. The components of the high frequency dielectric constant are determined and the absorption spectra of the films are computed. They display specific features just above the absorption threshold due to transitions from or to the surface resonances. This study provides a first understanding of finite size effects on the electronic properties of ZnO thin films and a benchmark which is expected to foster experimental characterization of ultra-thin films via spectroscopic techniques.
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