S. IDRISSI1,*, S. ZITI3, H. LABRIM2 and L. BAHMAD1,*
1 Laboratoire de la Matière Condensée et des Sciences Interdisciplinaires (LaMCScI), Mohammed V University of Rabat, Faculty of Sciences, B.P. 1014 Rabat, Morocco.
2 USM/DERS/Centre National de l’Energie, des Sciences et des Techniques Nucléaires (CNESTEN), Rabat, Morocco.
3 Intelligence Artificial and Security of Systems, Mohammed V University of Rabat, Faculty of Sciences, B.P. 1014 Rabat, Morocco.
Abstract: 11*) Corresponding authors:samiraidrissi2013@gmail.com (S. I) ;lahou2002@gmail.com (L.B);
In this paper, we use the density functional theory (DFT) calculations under Quantum Espresso package to characterize the doping effect of sulfur substituting on the Zirconium dioxide ZrO2. Through the density of states and the band structure calculations, a direct band gap is appearing for the pure and doped studied system. The electronic properties analysis shows that the doping with sulfur could considerably decrease the band gap of doped ZrO2 by the presence of an impurity state of sulfur 3 p on the up spin of the valence band.
The results of the ab-initio density functional theory investigations show that the substitutional sulfur dopants incorporated into the Zirconium dioxide ZrO2 drastically and affect the electronic structure of the studied material. In fact, the doping of Zirconium dioxide ZrO2 with appropriate concentration values of sulfur leads to band gap values in the interval (1-2) eV.
We recall that the band structure and density of states can improve among others: the energy gap of this doped ZrO2 material. In fact, we have started from 1.3 eV for the pure ZrO2 to reach 1.2 eV for 9% of sulfur doping. This last energy gap value is suitable for photovoltaic application.
Keywords: Zirconia ZrO2; Doping; Band gap; gradient generalized approximation (GGA); DFT method.
Introduction
As an essential ceramic compound, zirconium dioxide (ZrO2) has attracted immense attention, because of its higher refractory, thermal and mechanical properties [1- 7]. For the applications of light solar cells, the nanotechnology has focused on enormous improvement in the procedure of semiconductor nano-materials [8-12]. Because of the low production cost [13, 14], the development of renewable energy resources have a large interest in prepared solar cell technology owing to high power conversion efficiency.
On the other hand, the metal oxide layers such as Al2O3, TiO2, SiO2, MgO2, and ZrO2 have been used to act as an energy barriers forrestraining charge recombination [15-20]. In visible and near infrared region (NIR), the Zirconia dioxide material ZrO2 host possesses a high physical, chemical stability and optical transparency. The energy transfer from ZrO2 to rare earth ions has been proved by different doping ions such as Yb 3p, Er 3p,Tm 3p, Tb 3p, Eu 3p and Ho 3p [21-24]. In addition, the ZrO2 might be a good spectrum modifying matrix serving as a photon-conversion and an electron transporting layer. Therefore, the over coating of co-doped Yb-3p and Er-3p have the wide band gap value (4-6 eV) of the material ZrO2 [26-27]. The charge recombination participates to the loss of charge carriers and therefore decreases the photovoltaic performance of the cell [28-35].
Moreover, the several efforts on studying [36-38] have been devoted to the study of ferromagnetism tempted by the transition metal doping of semiconductor oxides ZrO2, called diluted magnetic semiconductors (DMSs) [39-40]. Because of the ferromagnetism in semiconductor metal oxides discovers, main applications in spintronics and optoelectronics are achieved. However, it remains unclear whether ferromagnetism is an intrinsic property of the system or it is due to the combination of magnetic impurities [41, 42]. Also, the Oxides ZrO2 have been also predicted as ferromagnets at room temperature when doped by the light 2p elements (N) [43].
The aim of this work is to analyze and discuss the band gap values of the zirconium dioxide ZrO2 by doping this material with different concentrations of the sulfur element (S). In fact, the doping sulfur is an efficient method for narrowing the band gap energy of semiconductor oxide and shifts the threshold wavelength to the visible light region, see Refs. [44-45]. This could be helpful to use solar energy for the elimination of organic hazards by photocatalysis.
In the present study, the effect of doping this material has been discussed, as function of the different concentrations: doped ZrO2 with 5 %, 9 %, 14 % and 18% of sulfur. These concentrations are below the percolation threshold of the pure dioxide ZrO2 compound. For this purpose, we study such properties by using the DFT method under the Quantum Espresso package.
Crystal structure and calculation method
In this paper, we are discussing the results of doping effect of Sulfur on Zirconium dioxide ZrO2. The structure of the pure Zirconium dioxide ZrO2 as demonstrated in Fig. 1, by the Xcrysden package [46]. The ZrO2 has the cubic structure with the space group “Fm3m” (N° 225). The lattice constant is chosen to take the value 5.149 Å [47] and very near to the other theoretical studies 5.139 and 5.154 Å [48, 49]. The zirconium atoms are occupying (0, 0, 0) while the oxygen atoms reside in positions: (1/4, 1/4, 1/4) and (3/4, 3/4, 3/4).
To study the doping effect of sulfur substituting on the Zirconium dioxide ZrO2. Through the density of states and the band structure calculations of the pure and doped zirconium dioxide ZrO2 with sulfur. We apply the Abinitio method using the Quantum Espresso code [50]. In fact, the obtained calculations are established based on the Density Functional Theory (DFT).
Indeed, we executed our simulations under the ultra-soft pseudo-potential method [51]. In these numerical calculations, we have used the gradient generalized approximation GGA founded on the parametrization given by Perdew et al. [52]. We use this approximation to treat the exchange correlation functional.
The valence electron configuration for Zirconium (Zr), oxygen (O) and sulfur (S) are: Zr (4d 5s), (2s 2p) and (3s 3p), respectively. The electrons were treated explicitly as valence states and expanded in plane-waves. In this work, the cutoff energy is equivalent to the separation of valence and core configurations, this value is found to be about 340 eV. The special points sampling integration, in the Brillouin zone, were employed using the Monkhorst–Pack method [53]. The convergence tolerance, in our simulations are fixed to 10-6 eV/atom. Some of our recent works have been based on the DFT study and other methods of numerical simulations [54-57].