Optoelectronic Properties of Sprayed MnxZn1−xO Optical Waveguide Thin Films: Refractive Index and Birefringence Tailoring

Abstract

MnxZn1-xO thin films (x = 0; 0.03; 0.05; 0.07, and 0.09) were deposited by spray pyrolysis on glass substrates. All of the films exhibited (002) oriented wurtzite structure with a diminishing crystallite size. The optical gap energy was evaluated by the first derivative method using transmittance which showed a linear increase of 0.06 eV starting from 3.24 eV. The photoluminescence spectra were deconvoluted and revealed the presence of multiple point defects most notably VO, with an agreement regarding the increase in optical gap energy. The reduction in charge carriers’
and mobility with the rise in magnetoresistance and resistivity were seen in the Hall effect based electric measurements. The SEM observations tracked the evolution of the surface morphology from flaky surface to dome shaped grains with a slight decrease in their size. Finally, the waveguiding properties of the films were investigated by m-lines technique which proved that all films were dual-mode waveguides. The ordinary and extraordinary refractive indices increased with Mn doping to reach 2.0019 and 2.0005 respectively, while the birefringence inversion started at Mn0.05Zn0.95O and stagnated at Mn content equals to 7 and 9 at. %.

Full text

Optoelectronic properties of sprayed MnxZn1−xOoptical
waveguide thin films: refractive index and birefringence
tailoring
Yassine Bouachiba1,2, Abdelouadoud Mammeri *1, Adel Taabouche1,3,
Abderrahmane Bouabellou1, Mohamed Aziz Mermouchi2, Ahd Saadou2, Badis
Rahal4, Hacene Serrar5, Lyes Benharrat6, and Halim Merabti5
1Laboratoire Couches Minces et Interfaces, Université de Fréres Mentouri
Constantine 1, Constantine, Algérie.
2Laboratoire Technologie des Matériaux Avancés, Ecole Nationale Polytechnique
de Constantine Malek BENNABI,BP 75A RP, Ali Mendjeli, Constantine, Algérie.
3Département de Physique et Chimie, Ecole Normale Superieure El Katiba Assia
Djebar Constantine, Constantine, Algérie.
4Physics Division, Nuclear Research Center of Algiers, 2 Bd, Frantz Fanon, BP
399, 16000, Algiers, Algeria.
5Research Center in Industrial Technologies (CRTI), BP 64 Cheraga, Alger,
Algeria.
6Research Center in Semiconductors Technology for Energy-CRTSE, 02 Bd. Dr.
Frantz Fanon, B.P. 140, 7 Merveilles, 16038 Algiers, Algeria.
January 13, 2023
*corresponding author: abdelouadoud.mammeri@gmail.com
1

2
Abstract
MnxZn1−xOthin films (x= 0,0.03,0.05,0.07, and 0.09) were deposited by spray pyrolysis
on glass substrates. All of the films exhibited (002) oriented wurtzite structure with a diminishing
crystallite size. The optical gap energy was evaluated by the first derivative method using trans-
mittance which showed a linear increase of 0.06 eV starting from 3.24 eV. The photoluminescence
spectra were deconvoluted and revealed the presence of multiple point defects most notably VO,
with an agreement regarding the increase in optical gap energy. The reduction in charge carriers’
and mobility with the rise in magnetoresistance and resistivity were seen in the Hall effect based
electric measurements. The SEM observations tracked the evolution of the surface morphology
from flaky surface to dome shaped grains with a slight decrease in their size. Finally, the waveg-
uiding properties of the films were investigated by m-lines technique which proved that all films
were dual-mode waveguides. The ordinary and extraordinary refractive indices increased with
Mn doping to reach 2.0019 and 2.0005 respectively, while the birefringence inversion started at
Mn0.05Zn0.95 Oand stagnated at Mn content equals to 7 and 9 at. %.
Keywords: ZnO, spray pyrolysis, birefringence inversion, prism coupler, magnetoresistance.
1 Introduction
Due to their high refractive index, chemical and thermal resistance, transparent ceramics films are
considered as a potential candidate for waveguide applications in various devices such as waveguide
amplifier [1] and low loss waveguide [2]. They were adapted to several deposition methods like ad-
ditive manufacturing [3], chemical vapor deposition [4], vapor solid process [5] and radio frequency
sputtering [6]. Transparent ceramics include a wide range of materials counting glasses [7,8], quartz
[9], nitrides [10], composites [11] and oxides [12].
Zinc Oxide (ZnO) is a very intriguing optical material where it was applied as a light emitting
diode and laser [13], waveguide [14–17] and waveguide amplifier [18,19]. ZnO is a uniaxial optical
material with ordinary and extraordinary refractive indices of no= 1.990 and ne= 2.006 respectively
[20]. Its inherent birefringence of uniaxial wurtzite structure is manifested when light propagates in
the material. The electric field vector of the incident light will experience different propagation ve-
locities for each axis, which can be used to change the phase shift between the two field components
with the propagation distance and therefore control the polarization. Phase retardation components
like waveplates and compensators are of high importance in polarization control which is an essen-
tial part of optical communication systems [21]. Anisotropic crystals with optical birefringence are
the building blocks of these components. Polarization control is of crucial importance in numerous

3
fields of photonics, including communications [22], imaging [23], and quantum information [24]. In-
tegrated polarization control bears the potential for compact, stable and low cost devices. ZnO was
deposited on a span of optically important substrates such as LiNbO3[25] silicon [26] silica [27],
diamond [28], GaAs [29], quartz [30] and glass [31].
Dilute magnetic semiconductors (DMS) are materials based on doping transition metals such as
V, Co, Cr, Mn, and Fe in a semiconductor to induce magnetic effects in the hosting material. With
that, a variety of applications were adopted in the microelectronics industry including spin-transistor
logic devices [32] and light emitting diode [33]. Mn doped ZnO proved to exhibit magnetic properties
in many papers [34–38]. CdMnTe DMS on GaAs substrate was validated as a waveguide to achieve
integrated optics [39] paving the way for the investigation and the application of DMSs as waveguides.
Spray pyrolysis is a deposition method in which a nanostructured material is obtained by spraying
a solution containing a precursor using a nebulizer onto a hot substrate. The precursor in the solution
undergoes a thermal decomposition and chamical reaction at the substrate to form the final material.
The film parameters like the shape, thickness, porosity and surface morphology can be controlled by
varying the spray parameters including the solution flow rate, substrate temperature and atomization
technique. Spray pyrolysis is a quite useful for the elaboration of nanostructured thin film oxide,
ceramic, composites, electroceramics, powders and even hollow particles and clusters for examples
Cu, TiO2, CdS, and CdSe [40–43].
In this work, we investigate the effect of Mn dopant on the electrical, optical and waveguiding
properties of ZnO. The inversion of the birefringence was demonstrated, in addition to an increase
in both refractive indices. The films underwent multiple characterizations; X-ray diffraction, UV-
Vis, photoluminescence, Hall effect measurements, scanning electron microscopy and prism coupler.
Figure 1represented an illustration of the most important finding of the paper.

4
ZMn0
o
ZMn0
e
ZMn9
o
ZMn9
e
Unpolarized light
Unpolarized light
After doping with 9 at. % Mn
ZMn0
o
ZMn0
e
<
<
ZMn9
o
ZMn9
e
ZMn0
o
ZMn0
e
<
ZMn0
e
>
n
ZMn0
o
n
ZMn9
o
ZMn9
e
>
ZMn9
e
<
n
ZMn9
o
n
>
ZMn9
e
n
ZMn0
e
n
>
ZMn9
o
n
o
ZMn0
n
Film
Substrate
Film
Substrate
Figure 1: Demonstrative figure of the birefringence inversion in Mn doped ZnO.
2 Experimental
2.1 Deposition conditions and characterization techniques
Pneumatic spray pyrolysis was employed to deposit updoped and Mn doped ZnO thin films on ordi-
nary glass microscope slides. The precursor for the Zn was Zinc acetate dihydrate [Zn(CH3CO2)2·
2H2O] (99.0% purity) and for Mn was Magnesium acetate tetrahydrate [Mg(CH3COO)2·4H2O](98.0%
purity) provided by AnalaR NORMAPUR. The solvent was 99.98% pure methanol. At 60°, the proper
amounts of Zinc acetate and Magnesium acetate were dissolved in methanol and stirred for 45 min-
utes at 60° to produce a molarity of 0.1 and Mn atomic doping percentage (at. %) of 0, 3, 5, 7 and 9.
A 46 mL of each solution was sprayed at a rate of 2 mL/min to grow films with thickness near 400
nm. The glass substrates were cleaned in a 1:1 acetone and ethanol ultrasonic bath for 15 minutes and
then dried in air. The deposition temperature was set at 450°.
To ensure the study’s validity, multiple characterization techniques were performed. The X-ray
diffraction was used to study the films’ crystal structure (Philips PANalytical X’Pert Pro diffrac-
tometer with a wavelength of 1.5406 Å). The UV-Vis measurements were performed by Shimadzu
UV-3101PC UV–Vis-NIR with a slit opening of 1 nm. The photoluminescence spectra were recorded
at room temperature with an excitation laser at 325 nm by FL3-DFX-iHR320. To examine the surface
morphology and Cross Section (CS) images JEOL JSM-7001F Scanning Electron Microscope (SEM)
was the tool. The electrical properties were determined by Ecopia HMS-3000 hall effect measurement

2.1 Deposition conditions and characterization techniques 5
system. As for the main objective of the work, the Metricon 2010/M Prism coupler was employed to
study the waveguiding characteristics of the films. Rutile TiO2was the coupling prism in our setup,
with ordinary and extraordinary refractive indices of no= 2.5822 and ne= 2.8639 respectively and
a side angle of θp= 44.60°. A monochromatic polarisable He-Ne laser with a wavelength of 632.8
nm served as the laser source. The setup was plotted in figure 2for demonstration.
Figure 2: Illustrative figure of the prism coupler setup.
where ~
kpis the wave vector at the prism’s base, ~
kfis the wave vector inside the MnxZn1−xOfilm,
θiis the incident angle, βis the propagation constant of the standing wave along the waveguide, np,
na,nfand nsare the refractive indices of the prism, air gap, film and substrate respectively. The
details conditions of the physical phenomenon and the obtention of the thickness and the refractive
indices were discussed in our previous work [44–46].

6
3 Results and discussion
3.1 XRD
20 24 28 32 36 40 44 48 52 56 60 64 68
ZMn0
Intensity (a. u.)
2(°)
ZMn3
ZMn5
ZMn7
ZMn9
(112)
(103)
(102)
(101)
(002)
(100)
Figure 3: X-ray diffraction patterns of all the films.
Figure 3represents the XRD spectra of the Mn doped ZnO for various concentrations. It was clear
that all films had poly-crystalline structure identified by hexagonal wurtzite (JCPDS card no. 00-036-
1451) indicating the incorporation of Mn+2 as a substitute for Zn+2[47]. The quasi-predominance
of (002) peak suggested the preferential growth of undoped and Mn-doped ZnO thin films through
the c-axis direction. Weak intensity peaks of other crystallographic directions were also observed at
the following positions: 31.96 (100), 36.56 (101), 47.87 (102), 63.17 (103) and 68.27°(112). We
expected the [002] direction to be the quasi-dominant direction in the thin films due to the fact that
ZnO has a P63mc symmetry; meaning that it is more stable pointing at [002] direction than other
directions [48].
The crystallite size (D) were evaluated by the Debye- Scherrer formula [31]:
D=Kλ
βcos(θ)(1)
where βis the Full Width at Half Maxima of the peaks, λis the wavelength of the incident X-rays, θ
is the Bragg’s diffraction angle and Kis the shape factor for a Gaussian fit with a value of 0.9. The

3.2 UV-Vis measurements 7
crystallite size was estimated from the peaks with the highest intensity (002). The most intense peak
was the reliable peak for such calculation, which can be justified by the fact that the XRD analysis
in our case was a macroscopic characterization technique, in addition to that, the high intensity of a
particular peak evidentially revealed that the crystal regions orientations in the films were pointing in
the same direction where their intensities accumulate. The calculations carried out on the basis of the
XRD spectra were tabulated in table 1. There was a decrease in the crystallite size with Mn doping,
this could have been the result of the fact that Mn atoms acted as thermodynamically more favorable
nucleation sites [49]. With the increase in Mn percentage, the nucleation site number grew, and with it
the number of crystallites increased, therefore, limiting the growth of each other. Overall, the average
strain on the main wurtzite axis decreased indicating more relaxed films over Mn concentration.
Table 1: The calculations inferred from XRD measurements.
Samples Crystallite size (nm) a(Å) c(Å) a(%) c(%)
ZMn0 37.6 3.2180 5.1537 -2.37 -3.42
ZMn3 25.1 3.2179 5.1567 -2.38 -3.12
ZMn5 22.8 3.2221 5.1592 -1.96 -2.87
ZMn7 22.6 3.2211 5.1588 -2.06 -2.91
ZMn9 21.7 3.2187 5.1580 -2.30 -2.99
3.2 UV-Vis measurements
Figure 4: UV-Vis measurements and the first derivative method for obtaining the gap energy.

3.2 UV-Vis measurements 8
The UV–Vis spectra in addition to the first derivative optical gap energy calculations were plotted in
figure 4. An overall increase in transmittance in the visible region of the films can be observed. The
optical band gap did also increase with the increase in Mn concentration. A similar tendency has been
reported in previous papers[50–52].
The optical band gap energy was evaluated by the first derivative method [53–55] and the peaks were
fitted with a Gaussian peaks to determine their center. The value of the optical gap energy varied by
0.06 eV, starting from 3.24 eV for the undoped ZnO to reach 3.30 eV for the 9 at. % Mn doped ZnO.
This variation was almost linear and it was approximated according to a linear interpolation (figure
5) as an empirical relation in the next equation:
Eg= 0.00722x+ 3.2389 (2)
Figure 5: Optical gap energy values as a function of Mn at.% concentration with linear fitting.
The increase in the gap energy probably was related to two reasons: first, based on the nearly
free electron in a periodic lattice approximation, the gap energy depends only on the first Fourier
coefficient of the crystal potential: Eg∝RVcry stal(r)ei~
k·~r which is proportional to the mean cohesive
(binding) energy. Any modification of the mean cohesive energy will result in an intrinsic modifica-
tion of the gap. The binding energy of Mn-O is greater than Zn-O [56], therefore, with increasing
Mn concentration in the films the gap energy increased. Secondly the Burstein-Moss effect where
Mn+2 has the same charge state as that of the cation in the host material (Zn+2) therefore Mn+2 is the
neutral state of Mn in ZnO [57]. Mn+2 cannot act as an acceptor since the first unoccupied energy
level lies above the Conduction Band Minimum CBM. We recall that the dshell of a substitutional

3.3 Photoluminescence 9
Mn+2 ion in zinc wurtzite crystal (tetrahedral complex) is split into an e2doublet and a t2triplet state.
All Mn+2 ions in ZnO are in the high spin state [58].
The optical gap is the minimum energy needed to excite an electron from the valence band to the
conduction band. In the pure, undoped crystal, the optical gap equals the energy separation between
the bands’ edges. Since the Pauli principle limits the occupation of electronic states to a maximum
of two electrons and the optical transitions are vertical, the introduction of donor electrons occupying
states below the Fermi level pushed it to the conduction band. This renders the energy difference
between states with Fermi energy in the conduction and valence band to be the optical gap energy.
The blocking of the low-energy transitions is known as the Burstein-Moss (BM) effect and an in-
crease in the optical gap energy is observed [59]. Similar explanations were proposed by Hu et al.
[51] and S.A.Ahmed [60]. Figure 6illustrates the shift of Fermi level due to the introduction of Mn+2
in ZnO with respect to undoped ZnO. We point out that the transitions from t2and e2to the Fermi
level are 953 and 539 nm respectively. The first transition seems to be in the infrared region which
might be excitable by the surroundings and the second by ordinary lab lamps. These electrons were
trapped by oxygen vacancies [47]. The oxygen vacancies existence was proved in the next subsection
of photoluminescence measurements.
0
1
2
3
4
5
6
7
Mn Doped ZnO
CBM
E
f
(Mn=9 at.%)
3.20
3.25
3.30
3.35
Ef
Mn=9 at.%
CBM
VBM
E
f
(Mn=0 at.%)
t
2
e
2
t
2
e
2
Energy (eV)
Zoomed
Burstein-Moss shift
Undoped ZnO
Figure 6: Illustrative figure of the Burstein-Moss effect of Mn doped ZnO.
3.3 Photoluminescence
A defect free ZnO single crystal has an emission peak in the visible region meanwhile an increase in
the number of emission peaks is associated with the presence of defect levels in the material.

3.3 Photoluminescence 10
Figure 7: Photoluminescence spectra with their deconvolution for all undoped and Mn doped ZnO
thin films.
The positions of these peaks yield information concerning the type of defects [61–64]. The pho-
toluminescence spectra of the Mn-doped ZnO film were presented in figure 7. All of the spectra were
deconvoluted for proper interpretation of the results. An agreement between the gap energy calculated
in the UV-Vis subsection and photoluminescence could easily be observed, where there was a blue
shift in the exciton recombination peak from 381 nm in ZMn0 to 377 in ZMn9. The second peak in

3.4 Hall effect measurements 11
MnZ0 film, i.e. the 402 nm peak was assigned to the electronic transition from the bottom of the CB
to the VZn energy level [65]. The peaks around 413 could be ascribed to electronic transitions be-
tween shallow donor level of neutral Znito the top level of the valence band [66]. The peaks between
428 and 436 nm were the results of transitions from zinc interstitial Zniand/or oxygen vacancies VO
to the valence band [67]. Peaks in the vicinity of 460 nm were due to oxygen vacancies [68]. The
peaks around 475 nm of ZnO emission have been reported, yet their origin has not been explained
[69]. The 481 nm peak was the result of electrons transitioning from Znito VZn [66]. The peak at 507
nm was ascribed to VOas well [70]. The green emission at approximately 522 nm was attributed to
the transition from CB to acceptor levels of OZn [71]. As for the 595 nm peak, it was due to oxygen
interstitials-zinc vacancies complexes [72]. Finally, the 650 nm peaks were the reflected double the
wavelength of the laser source (2×325). Similar results were reported [73,74].
3.4 Hall effect measurements
Figure 8: Resistivity, mobility, magnetoresistance and the natural logarithm of the bulk concentration
as a function of Mn at. %.
All the films showed n-type conduction since the present crystal phase was ZnO wurtzite. An increase
in resistivity and magnetoresistance with a decrease in charge carriers’ density, in addition to mobility
as the Mn content went from 0 to 9 at. % was depicted in figure 8. From previous studies [75],
Mn behaves as a deep donor, however, it does not give a direct contribution to the charge carriers
density of the films at room temperature. The charge carriers’ density was affected mainly by the
BM effect which prevents the charges above CBM and blow the Fermi level from being accessible
in addition to that the trapping of the electron transitioning from t2to CBM for a wavelength of just
above 950 nm by oxygen vacancies [47]. We should mention that as a function of the spin state, the
distribution of the electron in t2and e2are different. The Mn dshell holds 10 electrons in total, it

3.5 Surface morphology and Cross-sectional images 12
splits into t2and e2as mentioned above so the number of electrons in e2will be 4 and in t2will be
6. In a high spin state and in the case of Mn+2 (d5), e2is occupied by 2 electrons and t2by 3, but
for the low spin state e2is occupied by 4 electrons and t2by just one electron, which deepens these
electrons further [76] The diminishing of the mobility over Mn content could be explained by impurity
scattering by Mn+2 ions, in addition to the decrease in crystallite size inducing boundary scattering.
All of this made the Mn doped ZnO thin films more resistant at room temperature [77]. Mn is a
transition metal with a non-zero net spin, its introduction in the wurtzite structure provides localized
spins interacting with conducting carriers in ZnO [78] previously mentioned as sp-d coupling. This
effect is related to an intensive property of the Mn doped ZnO. Therefore, by performing Hall-effect
measurement using 1 Tesla magnet, the Mn+2 ions were all aligned. Doing that increased the spin
interaction in the sp-d coupling which by its turn manifested as magnetoresistance [79]. A decrease in
the magnetoresistance was observed in ZMn9 which was corresponded to the lowest charge carriers’
value [80]. The magnetoresistance effect was schematized in figure 9.
y
x
Spin interaction
Electron
Figure 9: Illustration of the magnetoresistance effect in the Mn doped ZnO films
3.5 Surface morphology and Cross-sectional images
The SEM images in figure 10, revealed flaky surface morphology for all films. In fact, this surface
morphology was more pronounced in pure films. With the introduction of Mn, the flaky surface
morphology was less evident with a dome shaped-growth tendency. Multiple grain size distribution
could be observed for all the deposited films. The average grain size in the undoped ZnO films was in
the range of 300 and 500 nm. The rest of the films experienced a small decrease in grain size (200-400
nm) with smoother surfaces. As depicted in figure 11, the CS images showed the thickness values at
four points of each of the films. These values were close to the ones obtained by the m-lines, yet we
mention that the m-lines relative error is 0.5% [81] which makes it of high accuracy relative to the
SEM images [82,83]. The average thickness from the CS images were listed in table 2.

3.5 Surface morphology and Cross-sectional images 13
Figure 10: SEM images of all the undoped and Mn doped ZnO thin films.
Figure 11: Cross-section images for all of the deposited films.

3.6 M-lines measurements 14
3.6 M-lines measurements
Figure 12: The reflected intensity as a function of angle of incidence, (left) transverse electric, (right)
transverse magnetic.
Figure 12 showed the curves recorded by the prism coupler for undoped and Mn doped ZnO thin
films. All films experienced bi-mode in transverse magnetic and transverse electric polarization from
which the optogeometric parameters can be deduced as previously detailed in our works [44]. The
thickness and the effective indices were listed in table 2. The small variation in thickness between the
films was reasonable given the fact that the deposition method was spray pyrolysis.
Figure 15 illustrated the propagation of light in the TE mode and TM mode following that, figure
14 presented both ordinary and extraordinary refractive indices in addition to the birefringence as a
function of Mn doping. There was an obvious increase in both refractive indices. This increase could
be attributed to the difference in electronegativity between Mn+2 (1.55) [84] and Zn+2 (1.65) [85].
The greater the difference in electronegativity, the more polarized the electron distribution and the
larger the partial charges of the atoms. When electronegativity decreases, polarizability increases.
Therefore, from the electronegativity point of view, the increase in polarizability decreases the ability
of ions to attract electrons from the atoms bonded to them [86]. The effect of the polarizability
difference between Zn+2 −O−2and Mn+2 −O−2on the bond vibration was schematized in figure 13
by adopting chemical bonds as springs. The birefringence experienced a slight increase at first and
then a negative values when the Mn content reached 5 at. %, after that it stabilized.

3.6 M-lines measurements 15
Figure 13: Schematic drawing of the effect of polarozability on the vibration of Mn-O and Zn-O.
In general, the refractive index and extinction coefficient are influenced by the density and the
local polarizability as it is related to chemical bonds and electron clouds deformations, which will
be happening by the induced electromagnetic waves when they were coupled and guided inside Mn
doped ZnO thin films. The relationship between the microscopic polarization (α) and the macroscopic
refractive index is known as the Lorenz-Lorentz equation [87]:
n2−1
n2+ 2 =4π
3Nα (3)
where Nis Avogadro’s number. We can see that a higher refractive index is associated with larger
ionic polarizability, which increased with the decrease of electronegativity of the doped films when
replacing Zn+2 with Mn+2. The birefringence of ZnO is positive as its refractive indices no= 1.990
and ne= 2.006. From figure 14, there was an inversion in birefringence from positive to negative
values. Birefringence can be affected by a number of factors such as bond orientation [88,89] strain
[90], and polarizability [91]. The inversion of the birefringence was intimately related to the smaller
Mn-O bond length in comparison to Zn-O along the c direction [92] i.e. smaller dipole moment
(~p =~
lq). A smaller bond length in the [0001] direction was translated to smaller extraordinary
refractive index.

3.6 M-lines measurements 16
Figure 14: Ordinary and extraordinary refractive index over Mn atomic concentration.
Table 2: Summary of the measured thicknesses, refractive index in and effective indices.
Film Thickness (nm) Refractive index Effective index
TE TM CS noneTE0TE1TM0TM1
ZMn0 404,6 423,2 411.0 1.9729 1.9759 1.8860 1.6240 1.8670 1.5680
ZMn3 477,2 487,3 575.5 1.9846 1.9904 1.9170 1.7100 1.9050 1.6550
ZMn5 340,2 371,6 288.5 1.9943 1.9893 1.8820 1.5540 1.8530 1.5180
ZMn7 359,4 380,5 446.25 1.9993 1.9979 1.8950 1.5870 1.8670 1.5320
ZMn9 352,2 370,8 494.0 2.0019 2.0005 1.8950 1.5790 1.8640 1.5220
(a) Transverse Magnetic (b) Transverse Electric
Figure 15: Demonstrative figure of the the light propagation in: (a) transverse electric and (b) trans-
verse magnetic modes with respect to the wurtzite conventional cell.

REFERENCES 17
Conclusion
In summary, Mn doped ZnO films were successfully elaborated by spray pyrolysis and tested for their
waveguide properties. The Wurtzite structure was apparent in all films with no secondary phases.
The crystallite size decreased with Mn doping. A general rise in the transmittance over Mn at.%
concentration followed by a linear optical gap increase, the reason for that was linked to the Mn-O
elevated binding energy in addition to Burstein Moss effect. Multiple point defect were detected by
photoluminescence analysis including VO,Zniand VZn with an alignment in the optical gap energy
behavior with UV-Vis. The surface morphology was found to be flaky in the undoped film and tend
towards dome like grains with a small decrease in grain size. The m-lines spectroscopy measured two
modes in each film in both TE and TM polarization. The ordinary and extraordinary refractive indices
increased with Mn doping and negative birefringence was recorded in 5, 7 and 9 at. % Mn doped
ZnO films. This work demonstrates the simplicity and effectiveness of Mn doping for controlling
the magnetoresistance and birefringence properties of ZnO thin films while preserving the wurtzite
structure.
Competing Interests
There are no conflicts of interest between the authors.
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