First and second harmonic generation of the XAl2Se4 (X=Zn,Cd,Hg) defect chalcopyrite compounds☆
Introduction
Several investigations have been carried out to understand the perspective phenomenology existing in the study of nonlinear optical properties (NLO) of semiconductors. In order to improve their yields in the industrial area. It is established that a strong relationship exists between the electro-negativity and the band gap in semiconductors. Thus it is interesting to exploit the influence of physical and chemical tendencies such as the electro-negativity on the NLO in semiconductors. Novel compounds having suitable qualities such as phase matching for applications in the field of laser or in devices based on optical parametric oscillators (OPO) are investigated. One of the recently studied family is the defect chalcopyrite (DC) [1], [2], in particular, aluminum (Al)-containing compounds like CdAl2Se4, HgAl2Se4, ZnAl2Se4 and others [3], [4]. Because of their wide region of transparency due to a large gap [5], [6], [7], [8], [9], they possess high optical strength, high photosensitivity, and strong luminescent properties, which make them promising materials with potential application in optoelectronics and nonlinear optical fields. A more complete understanding of the physical properties is prerequisite to the eventual technological application of these compounds.
The first-principle calculation of physical properties and chemical bonding is a popular route towards understanding the electronic, chemical and structural properties of materials. Both experimental and theoretical works like chemical bond method [10] are in good agreement concerning the transferability of the atomic contributions to the nonlinearity of the optical properties. From a fundamental point of view, the increase/decrease of the electro-negativity of a compound influences the second harmonic generation. There have been several attempts to obtain the correlation between band gaps, single bond energy, atomic numbers, electro-negativities and refractive indices [11], [12]. Moss et al. [13] have been systemizing the extensive experimental data on energy gap and high frequency refractive index for several semiconductors. An empirical relationship between these quantities was proposed. Other corrections have been established by Reddy [11], which consents that there exists a possible correlation between refractive indices and the nature of the material bonding. Nevertheless, no quantitative relationship can be generalized for the nonlinear optical properties according to the experimental data [14] and theoretical results [15].
Due to the complex structure of the periodic crystal and the lack of accuracy of standard method for bonding calculations, it is natural to use more complex models and methods to interpret these more complex data. We have shown in a previous work [16], using a Bader's quantum theory of atoms in molecules (QTAIM) [17], [18], [19], [20], how to analyze the chemical bonding properties and topological partition of the compressibility of the AgGaSe2 in its chalcopyrite phase. This investigation has been traditionally dominated by the intent of developing empirical measurements of the key factors controlling the main trends in the materials like the Pauling electro-negativities [21]. Our main objective in this work is to show whether the (QTAIM) approach can be useful to determine if the chemical bonding properties influence the second harmonic generation processes for three defect chalcopyrite compounds CdAl2Se4, HgAl2Se4 and ZnAl2Se4. To make topological analysis on the electron densities, we have used techniques developed by Luaña and co-workers [22], [23], [24], [25], [26], [27] in order to calculate complex bonding properties and the charge displacement when replacing the cation atoms from Zn to Hg in the II-B column of the Mendeleiev table. We also provide an ab initio calculation of the linear and nonlinear optical properties based on the Aspnes [28], Sipe and Gharamani [29] and Aversa and Sipe [30] methods.
The paper is organized as follows: the computational details are briefly described in Section 2. The core of the paper appears in Section 3, where the results are presented and analyzed. Section 4 concludes with a brief review of the main results.
Section snippets
Computational details
It is well known that the density functional theory (DFT) yields correct ground state properties such as the lattice constant, and the phonon frequency of a system. Since the DFT does not describe correctly excited states [31], [32], it is necessary to go beyond LDA or GGA (XC) functionals to quasi-particle-like GW electronic structure calculations. The GW approximation successfully yields quasi-particle energy gaps in semiconductors which agree with the experimental values [33], [34], [35],
Results and discussion
We have determined the equilibrium properties of the investigated compounds. The most relevant results in comparison with the available experimental data and theoretical results are presented in Table 1. In general, the equilibrium cell lattice is obtained within 4% of the experimental values [3], [41], [42], [36]. The agreement with the available experimental data is reasonable within the limits expected for the chosen XC functional. An immediate conclusion is clear just from these data: there
Conclusion
We have carried out a systematic ab initio density functional theory study of the structural, bonding and optical properties of ZnAl2Se4, CdAl2Se4 and HgAl2Se4 in the defect-chalcopyrite phases within density functional theory in the GGA-PBE density approximation. We used the highly accurate GW0 method to correct the gaps. The calculated properties were in good agreement with experimental data and theoretical results. Comparatively to the conventional methods, the so-called topological analysis
Acknowledgments
The authors would like to thank MALTA-Consolider Team and Departamento de Química Física y Analítica. Universidad de Oviedo (Spain). Especially, Professor J. M. Recio for providing the computational facilities. The authors R. Khenata, S. Bin-Omran and A. Bouhemadou extend their appreciations to the Deanship of Scientific Research at King Saud University for funding the work through the research group project no. RGP-VPP-088. For the author Ali H. Reshak his work is supported from Project CENAKVA
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