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].