Flores Efracio Mamani, Moreira Mário L, Piotrowski Maurício Jeomar
Department of Physics, Federal University of Pelotas, P.O. Box 354, 96010 900 Pelotas, RS, Brazil.
Department of Physics, National University Jorge Basadre Grohmann, 23001 Tacna, Perú.
J Phys Chem A. 2020 May 14;124(19):3778-3785. doi: 10.1021/acs.jpca.9b11415. Epub 2020 May 4.
Here, we have studied the crystalline structure of bulk ZnX (X = O, S, Se, Te) and ZnF systems as a first step to understand the structures like ZnX and Zn-based systems like ZnO/ZnF interfaces, which are of utmost importance for possible technological applications. In addition, an adequate methodological description based on density functional theory (DFT) calculations is necessary. It is well known that plain DFT calculations based on local or semilocal exchange-correlation functionals fail to describe the correct band gap energy for these systems, whereas nonlocal approaches, such as hybrid-based functionals, can compensate the underestimation of band gap. To contribute to the assessment, DFT studies were performed within semilocal Perdew-Burke-Ernzerhof (PBE) and two nonlocal functionals, hybrid Heyd-Scuseria-Ernzerhof (HSE) and PBE + functionals. Our results confirm that PBE underestimates the energy band gap values, from 33.0 to 42.8% for ZnX compounds compared to the experimental values. Applying the hybrid HSE functional, we obtained a band gap dependency in relation to the range of separation of the nonlocal exact exchange, in general decreasing the band gap error and improving the lattice constant description. In addition, using the PBE + approach, we have investigated the localization of the Zn d-states and its effect on the band gap in ZnX and ZnF. We found an increase in the band gap with increasing Hubbard parameter, which introduces on-site Coulomb corrections for the Zn 3d states. In the same context, the relevance to include the Hubbard corrections for the O 2p states (and X p states) is highlighted. Thus, considering PBE + , the error in ZnO band gap, for example, decreases to 5.1%, in relation to the experimental value. Finally, ZnO-12L/ZnF-4L superlattices are found to exhibit conventional electronic properties, such as low fundamental band gap, smaller than either of the parent materials. Our first-principles calculations reveal that the unexpected band gap reduction is induced by the conducting layers that tend to penetrate the interface and decrease the band gap, leading to the transport of carriers through the interface to ZnF, which, even with a high band gap for charge transfer, can be interesting for photovoltaic applications.
在此，我们研究了块状ZnX（X = O、S、Se、Te）和ZnF体系的晶体结构，作为理解诸如ZnX结构以及像ZnO/ZnF界面这样的锌基体系的第一步，这些对于可能的技术应用极为重要。此外，基于密度泛函理论（DFT）计算的适当方法描述是必要的。众所周知，基于局域或半局域交换关联泛函的普通DFT计算无法正确描述这些体系的带隙能量，而非局域方法，如基于杂化的泛函，可以弥补带隙的低估。为了有助于评估，在半局域的Perdew-Burke-Ernzerhof（PBE）以及两种非局域泛函，即杂化的Heyd-Scuseria-Ernzerhof（HSE）和PBE + 泛函下进行了DFT研究。我们的结果证实，PBE低估了能带隙值，与实验值相比，ZnX化合物的能带隙值低估了33.0%至42.8%。应用杂化HSE泛函，我们获得了与非局域精确交换分离范围相关的带隙依赖性，总体上减小了带隙误差并改善了晶格常数描述。此外，使用PBE + 方法，我们研究了Zn d态的局域化及其对ZnX和ZnF中带隙的影响。我们发现随着哈伯德参数的增加带隙增大，该参数对Zn 3d态引入了在位库仑校正。在相同背景下，强调了对O 2p态（以及X p态）包含哈伯德校正的相关性。因此，例如考虑PBE + 时，ZnO带隙的误差相对于实验值降至5.1%。最后，发现ZnO - 12L/ZnF - 4L超晶格表现出传统的电子性质，如低的基本带隙，比任何一种母体材料都小。我们的第一性原理计算表明，意想不到的带隙减小是由倾向于穿透界面并减小带隙的导电层引起的，导致载流子通过界面传输到ZnF，即使对于电荷转移具有高带隙，这对于光伏应用也可能是有意义的。
