An original way to obtain porous Zn₍₁₋ₓ₎MgₓO thin films by spray pyrolysis technique
Zn₍₁₋ₓ₎MgₓO thin films with various concentrations of magnesium were deposited using the spray pyrolysis method. The transmittance spectra recorded for all films exhibit maxima exceeding 90%. The band gap energy of the films with wurtzite structure increases from 3.22 to 3.60 eV by incorporating Mg...
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| Опубліковано в: : | Semiconductor Physics Quantum Electronics & Optoelectronics |
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| Дата: | 2017 |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2017
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| Цитувати: | An original way to obtain porous Zn₍₁₋ₓ₎MgₓO thin films by spray pyrolysis technique / Abdelhakim Mahdjoub, Abdelaali Hafid, Mohammed Salah Aida, Abdelhamid Benhaya // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2017. — Т. 20, № 1. — С. 55-63. — Бібліогр.: 35 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860272229554585600 |
|---|---|
| author | Abdelhakim Mahdjoub Abdelaali Hafid Mohammed Salah Aida Abdelhamid Benhaya |
| author_facet | Abdelhakim Mahdjoub Abdelaali Hafid Mohammed Salah Aida Abdelhamid Benhaya |
| citation_txt | An original way to obtain porous Zn₍₁₋ₓ₎MgₓO thin films by spray pyrolysis technique / Abdelhakim Mahdjoub, Abdelaali Hafid, Mohammed Salah Aida, Abdelhamid Benhaya // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2017. — Т. 20, № 1. — С. 55-63. — Бібліогр.: 35 назв. — англ. |
| collection | DSpace DC |
| container_title | Semiconductor Physics Quantum Electronics & Optoelectronics |
| description | Zn₍₁₋ₓ₎MgₓO thin films with various concentrations of magnesium were deposited using the spray pyrolysis method. The transmittance spectra recorded for all films exhibit maxima exceeding 90%. The band gap energy of the films with wurtzite structure increases from 3.22 to 3.60 eV by incorporating Mg into ZnO. However, when the atomic ratio of Mg exceeded 0.4, a second crystalline phase (assigned to cubic MgO) became discernible in XRD patterns, a compressive strain was observed in the wurtzite lattice, and crystallite sizes decreased significantly. In accordance with these observations, finer grains with a pronounced columnar growth were observed in 3D AFM representations, and the surface roughness decreases significantly. Finally, selective etching in water yields porous films with a great surface-to-volume ratio, a lower refractive index, and a better light transmission. These porous films with tunable band gaps seem to be excellent candidates for various interesting applications.
|
| first_indexed | 2026-03-21T11:50:46Z |
| format | Article |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 1. P. 55-63.
doi: https://doi.org/10.15407/spqeo20.01.055
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
55
PACS 73.61.-r, 78.20.-e, 81.15.-z
An original way to obtain porous Zn(1–x)MgxO thin films
by spray pyrolysis technique
Abdelhakim Mahdjoub1,*, Abdelaali Hafid1, Mohammed Salah Aida2, Abdelhamid Benhaya3
1Laboratoire des Matériaux et Structures des Systèmes Electromécaniques et leur Fiabilité (LMSSEF) Université
d’Oum El Bouaghi BP 358, Algérie
*E-mail: abdelmah@yahoo.com
2Laboratoire des Couches Minces et Interfaces (LCMI),
Université de Constantine I, Constantine 25000, Algérie
3Laboratoire d’Electronique Avancée (LEA),
Université de Batna, Batna 05000, Algérie
Abstract. Zn(1–x)MgxO thin films with various concentrations of magnesium were
deposited using the spray pyrolysis method. The transmittance spectra recorded for all
films exhibit maxima exceeding 90%. The band gap energy of the films with wurtzite
structure increases from 3.22 up to 3.60 eV by incorporating Mg into ZnO. However,
when the atomic ratio of Mg exceeded 0.4, a second crystalline phase (assigned to cubic
MgO) became discernable in XRD patterns, a compressive strain was observed in the
wurtzite lattice, and crystallite sizes decreased significantly. In accordance with these
observations, finer grains with a pronounced columnar growth were observed in 3D
AFM representations and the surface roughness decreases significantly. Finally, selective
etching in water yields to porous films with a great surface-to-volume ratio, a lower
refractive index and a better light transmission. These porous films with tunable band gap
seem to be excellent candidates to various interesting applications.
Keywords: zinc oxide, magnesium, thin films, transmittance, porosity.
Manuscript received 22.11.16; revised version received 01.02.17; accepted for
publication 01.03.17; published online 05.04.17.
1. Introduction
Metallic oxides have many applications in a wide variety
of technological areas [1-3]. The most remarkable utility
of these materials is by far the TCO (transparent and
conducting oxides) application [3-5]. Tin-doped indium
oxide (ITO) is certainly the most common TCO, but
because of the rarity of indium on earth, ITO remains
too expensive. Therefore, researchers try to replace it
with more accessible materials. AZO (aluminum doped
zinc oxide), IZO (indium doped zinc oxide) and GZO
(gallium doped zinc oxide) exhibit interesting optical
and electrical properties and seem to be the materials,
performances of which are closest to those of ITO [4, 6].
Besides, doped ZnO is usually used as an active material
in photodetectors [8, 9] and photocatalysis [10, 11]. For
these applications, the active surface affected by the
grain size and the film porosity becomes the most
important factor improving the device performance [12].
On the other hand, the optical band gap of ZnO can be
increased by replacing zinc atoms by magnesium (Mg)
[13]. Several works have been published in this area
using different deposition methods such as sputtering
[14, 15], sol-gel [16], chemical bath deposition [17] and
spray pyrolysis [18, 19].
Zn(1–x)MgxO would therefore be a tunable band gap
semiconductor allowing multiple applications. The aim
of this work is to study the magnesium concentration
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 1. P. 55-63.
doi: https://doi.org/10.15407/spqeo20.01.055
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
56
effect on the optical, structural and morphological
properties of MgxZn(1–x)O thin films obtained by spray
pyrolysis deposition and its impact on potential
applications.
2. Experimental procedure
The originality of this work is of having employed a
medical nebulizer (Omron CompAir NEC801) for
depositing thin films by spray pyrolysis. Beside its low
price, the advantage of this apparatus is to help obtain a
flux of very fine droplets oriented vertically towards the
substrates placed on a thermoregulated heating plate.
The substrate holder temperature is maintained at 350 °C
allowing a complete decomposition of the precursors.
Zinc and magnesium acetates 0.2M aqueous solutions
were prepared to serve as precursors for the films
deposition. These solutions were mixed in different
volume ratios (0:5; 1:4; 2:3, 3:2; 4:1 and 5:0) to obtain
Zn(1–x)MgxO alloys ranging from ZnO to MgO. The total
dissolution of the precursors in the solvent is therefore
essential for obtaining the right chemical composition. A
clear solution without any precipitate is then sought. If
this procedure is scrupulously respected, the chemical
composition of the deposited film will correspond
perfectly to the chosen proportions of precursors.
Two similar sets of films were deposited on silica
and silicon substrates to allow a larger variety of
characterization. Morphology of the deposited layers
was observed using atomic force microscopy with the
A100 model of APEResearch. The crystalline structure
was explored by X-ray diffraction (EQ-MD10
diffractometer with a Cu-tube). Analysis of
transmittance and ellipsometric spectra, recorded using
respectively JASCO 630 spectrophotometer and
Angstrom-Advanced spectroscopic ellipsometer, allows
the study of the optical properties of the deposited films.
3. Results and discussion
3.1. Effect of magnesium concentration
on the Zn(1–x)MgxO structure
XRD patterns recorded between 20° and 75° on the six
Zn(1–x)MgxO thin films deposited on silicon substrates
are shown in Fig. 1. The spray pyrolysis technique
performed at 350 °C favors crystallization of the
deposited materials. Furthermore, the silicon substrates
were used to avoid the background noise due to
amorphous materials. Good quality diffractograms were
obtained in comparison to similar studies carried out on
Zn(1–x)MgxO thin films [17, 20]. For atomic magnesium
ratios x less than 0.4, the XRD patterns show exclusively
characteristic peaks inherent to the ZnO wurtzite
structure [JCPDS File No.36-1451]. For x higher than
0.4, the characteristic peaks of MgO cubic structure
clearly appear on the XRD patterns and become
dominant when approaching pure MgO [JCPDS File
No.74-1225]. Note that 40% of Mg failed to bring out an
MgO phase accompanying the wurtzite structure, while
20% Zn impose their presence in the cubic structure of
MgO. The incorporation of Mg (Mg2+ slightly smaller
than Zn2+ [20]) in ZnO is much larger than that of Zn in
MgO. Choopun et al. reported that the solid solubility of
MgO in ZnO for thin-film samples did not exceed 33%
[21]. Above this concentration, MgO segregates from
wurtzite lattice in cubic phase. This is in agreement with
our results, if it is assumed that for x = 0.4 the MgO
cubic phase was not sufficient to be observed within the
detection limit of our measurement. In Fig. 1, we notice
a slight shift of the strongest peak (002) from 34.62° for
ZnO to 34.98° in the case of Zn0.4Mg0.6O alloy,
indicating a diminution in the hexagonal lattice
parameter c. This behavior has been observed by
Maemoto et al. [22].
The broadening of the diffraction peaks, directly
related to the crystallite size and lattice strain, was
analyzed using the Williamson–Hall (W-H) method
[23], being based on the following equation:
λ
θε
+=
λ
θβ sin49.0cos
d
, (1)
where 2
0
2 β−β=β m
represents the peak broadening after
removing the instrumental contribution (β0 = 0.001
radians), (βm – measured full width at half maximum (in
radians), ε – lattice strain, θ – Bragg angle, d – average
crystallite size, and λ – wavelength of X-rays.
20 30 40 50 60 70 80
Zn
O
(1
00
)
x=1
x=0,8
x=0,6
x=0,4
x=0,2
Ar
b,
u
ni
t
2θ (°)
x=0
M
gO
(1
11
)
Zn
O
(0
02
)
Zn
O
(1
01
)
M
gO
(2
00
)
Zn
O
(1
02
)
M
gO
(2
20
)
Zn
O
(1
03
)
Zn
O
(1
12
)
Fig. 1. XRD patterns of Zn(1–x)MgxO thin films deposited on
silicon substrates for x = 0, 0.2, 0.4, 0.6, 0.8, 1.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 1. P. 55-63.
doi: https://doi.org/10.15407/spqeo20.01.055
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
57
0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
0,000
0,002
0,004
0,006
0,008
0,010
0,012
0,014
MgO
Zn0,2Mg0,8O
Zn0,4Mg0,6O
Zn0,6Mg0,4O
ZnO
(β
∗c
os
θ)
/λ
(2*sinθ)/λ
Zn
0,8
Mg
0,2
O
Williamson-Hall plot
Fig. 2. Williamson–Hall plots of Zn(1–x)MgxO for wurtzite and
MgO cubic phases.
Using the W-H plot, the lattice strain and crystallite
sizes were calculated respectively from the slope of the
linear fit and the y-intercept (Fig. 2). This analysis was
applied to (002), (101), (102), (103), (112)
corresponding peaks of wurtzite phase as well as those
corresponding to (111), (200) and (220) planes of the
MgO cubic phase.
The results of W-H analysis are summarized in
Table 1 for the wurtzite phase and Table 2 for MgO. As
can be seen, increasing the Mg concentration (for
x < 0.6) is accompanied with wurtzite crystallite sizes
and lattice strain decrease (Fig. 3). Furthermore, for x
between 0.4 and 0.8, when the cubic phase appeared
beside the hexagonal one, the slope of W-H plots was
reverted, and the strain became compressive. When only
MgO was deposited, the crystallite size increased to
27.9 nm, and the strain became tensile again (Table 2).
These results demonstrate that the presence of both
hexagonal and cubic phases at the same time induces
compression in the lattice of each phase and hinders the
growth of larger particles. Similar correlation between
the compressive strain and crystallite sizes was reported
by Cheong et al. in their study of TiO2 thin films [24].
Reyes-Rojas et al. reported that the addition of ZrO2 and
Y2O3 increased the compressive strain in alumina
polycrystal and affected the grains growth [25].
3.2. Morphological aspect
Nanoscale 3D representation of the surface recorded by
AFM for the six samples prepared on silicon substrates
is shown in Fig. 4. The grains have a rounded shape with
a columnar growth. The size of MgO grains (exceeding
260 nm) is greater than that of ZnO (around 190 nm).
For Zn(1–x)MgxO alloys, the grain size is slightly smaller
than that of ZnO (between 150 and 180 nm) as long as
the cubic phase does not appear (x < 0.4). When the
cubic phase becomes important, finer grains (less than
100 nm) with a pronounced columnar growth are
observed, and therefore the surface roughness decreases
significantly (RMS indicated in Table 3). The
simultaneous presence of two competitive phases
(wurtzite and cubic) favors a growth of fine columns
resulting in a low surface roughness. Similar behavior
was observed by Tsay et al. in their work [20].
These observations clearly illustrated in Fig. 5,
confirm the tendency emerging from the XRD analysis.
However, it should be noticed that the grains size
estimated by AFM is much greater than that of the
crystallites calculated from XRD patterns. Presumably,
each grain observed by AFM contains several
nanocrystallites revealed by XRD.
Table 1. Williamson–Hall XRD analysis of the wurtzite phase.
(hkl) Atom. ratio 0 0.2 0.4 0.6 0.8
θ (deg.) 17.31 17.31 17.33 17.49 17.29
(002)
βm (deg.) 0.369 0.468 0.563 0.752 0.593
θ (deg.) 18.185 18.185 18.14 18.27 18.13
(101)
βm (deg.) 0.409 0.453 0.543 0.731 0.563
θ (deg.) 23.94 23.9 23.83 24.00 23.87
(102)
βm (deg.) 0.503 0.553 0.553 0.692 0.543
θ (deg.) 31.63 31.61 31.55 31.82 31.44
(103)
βm (deg.) 0.642 0.612 0.543 0.582 0.513
θ (deg.) 34.17 34.08 34.00 34.19 34.10
(110)
βm (deg.) 0.652 0.662 0.523 0.523 0.493
Crystallites size (nm) 54.8 25.3 12.6 7.8 11.2
Lattice strain (10–3) 3.2 1.8 –1.5 –4.5 –2.4
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 1. P. 55-63.
doi: https://doi.org/10.15407/spqeo20.01.055
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
58
Table 2. Williamson–Hall XRD analysis of the MgO cubic
phase.
(hkl)
Atom. ratio (111) (200) (220)
θ (deg.) 15.71 21.38 31.06
βm (deg.) 0.374 0.423 0.483
Crystallites size (nm) 27.9
Lattice strain (10–3) 1.06
0.0 0.2 0.4 0.6 0.8 1.0
0
10
20
30
40
50
60
C
ry
st
s
iz
e
(n
m
)
Mg at. ratio
Wurtzite phase
MgO
St
ra
in
(1
0-3
)
Williamson-Hall results
-10
-8
-6
-4
-2
0
2
4
Fig. 3. Crystallite size and lattice strain deduced from the
Williamson–Hall plots.
3.3. Optical properties
For transmittance measurements, silica substrates of 1-
mm thick were used. Fig. 6 shows the transmittance
spectra of Zn(1–x)MgxO films for the different values of
the atomic ratio x, compared to that of the bare silica
substrate. Silica is transparent over practically the entire
range of wavelengths available by the JASCO 630
spectrophotometer. Interferential fringes are visible on
all the spectra recorded for the deposited films. It
demonstrates good quality of the deposited films with
homogeneous and smooth surface. The fit of the
measured spectra by an appropriate mathematical model
(detailed out in a previous work [26]) allows
determining the thicknesses indicated in Fig. 6.
The transmittance maxima recorded on all the films
are very close to the transmittance of silica (maximum
value is 93.5%). MgO is practically transparent across
the measured spectrum, whereas ZnO has an absorption
edge around 380 nm corresponding to a band gap energy
of 3.22 eV (in good agreement with the published
values) [27]. For Zn(1–x)MgxO alloys with atomic ratio x
between 0.2 and 0.4, a single absorption edge dominates.
The band gap energy increases up to 3.54 eV in
agreement with the results reported by Tsay et al. [20].
When the atomic ratio exceeds this value (x between 0.6
and 0.8), two optical transitions appear, corresponding to
the two crystalline phases (wurtzite and cubic) revealed
by XRD. The lowest transition situated at 3.6 eV
corresponds to wurtzite phase. The second one
approaches that of the MgO thin films, estimated by
Badar et al. at 5.5 eV [28]. The transmittance spectra
recorded for the samples with columnar growth (for x =
0.6 or 0.8) exhibit larger amplitude fringes probably due
to the diminution of surface roughness [26].
For ellipsometric measurements, monocrystalline
silicon substrates were used. Fig. 7 shows the
ellipsometric spectra of Zn(1–x)MgxO films for the
different values of the atomic ratio x. The ellipsometric
angles ψ and ∆ are plotted as functions of the incident
photon energy hν. In the part of the spectrum where the
films are transparent, interferential fringes can be
observed. However, in the absorption area, the
interferential fringes disappear [29]. For Zn(1–x)MgxO
alloys with atomic ratio x between 0.2 and 0.4, the limit
between the two areas is clearly discernible, and thus the
values of the band gap energy can be estimated. These
values are indicated in Table 4 and correspond well to
those previously calculated using the results of UV-Vis
spectroscopy (see Fig. 8).
When the atomic ratio x lies between 0.6 and 0.8,
the two crystalline phases (wurtzite and cubic) co-exist,
and the transition between the transparency and the
absorption areas (situated between 3.5 and 4.5 eV)
becomes difficult to discern. This behavior was clearly
explained by Choi et al. in the previous work [29]. An
appropriate mathematical analysis of the ellipsometric
spectra would be necessary to separate the two
absorption edges [30], but such investigation is not the
purpose of this work.
Table 3. Results of the AFM analysis.
Atomic
ratio x 0 0.2 0.4 0.6 0.8 1
Grain
size (nm) 188 176 154 78 97 263
RMS
(nm) 18.4 15.1 13.8 5.2 8.6 15.5
Table 4. Band gap energy of Zn(1–x)MgxO.
Atomic ratio x 0 0.2 0.4 0.6 0.8 1
Optical gap
(eV) (from
transmittance)
3.22 3.39 3.53 3.58 3.60 5.42
Optical gap
(eV) (from
ellipsometry)
3.26 3.36 3.54 – – –
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 1. P. 55-63.
doi: https://doi.org/10.15407/spqeo20.01.055
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
59
Fig. 4. AFM 3D representation of Zn(1–x)MgxO thin films
deposited on silicon substrates
0,0 0,2 0,4 0,6 0,8 1,0
50
100
150
200
250
300
Mg atomic ratio
G
ra
in
s
si
ze
(n
m
)
5
10
15
20R
M
S (nm
)
AFM analysis
Fig. 5. Grains size and RMS deduced from AFM.
2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5
MgO
Zn0,2Mg0,8O
Zn0,4Mg0,6O
Zn0,6Mg0,4O
Zn0,8Mg0,2O
ZnO
(α
.h
ν)
2
h.ν (eV)
(b)
200 400 600 800 1000 1200
0
20
40
60
80
100
T
(%
)
Wavelength (nm)
MgO -135nm
Zn0,2Mg0,8O-140nm
Zn0,4Mg0,6O-145nm
Zn0,6Mg0,4O-150nm
Zn0,8Mg0,2O-180nm
ZnO -195nm
Quartz
(a)
Fig. 6. Transmittances of Zn(1–x)MgxO thin films deposited on
silica (a) and band gap energy determination (b).
3.4. Porous Zn(1–x)MgxO thin films
Based on the above results, especially the coexistence of
two crystalline phases (wurtzite close to ZnO and cubic
close to MgO), and knowing that MgO, contrary to ZnO,
is soluble in water [31], the idea of making a porous
material by a selective etching becames evident.
Zn0.2Mg0.8O samples prepared on silica and silicon
substrates were etched in deionized water at 60 °C for
two hours. The changes introduced to the surface
morphology were observed by AFM and reported in 3D
representation (Fig. 9).
Morphology was totally changed and presented
growth in oriented column-forms. The mean grain size
estimated by AFM decreased drastically from 97 nm
(indicated in Table 3) down to 22 nm. The deposited
films then became nanoporous and presented a greater
surface-to-volume ratio. This behavior can be explained
by dissolution of the cubic phase MgO surrounding
columns of wurtzite phase. The small size of the grains
observed by AFM after treatment approaches the XRD
crystallites size reported in Table 1.
Silica
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 1. P. 55-63.
doi: https://doi.org/10.15407/spqeo20.01.055
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
60
1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5
5
10
15
20
25
30
35
40
45
50 Ψ- ZnO
Δ- ZnO
Energy (eV)
Ψ
(°
)
Eg=3,25eV 0
20
40
60
80
100
120
140
Δ (°)
1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5
0
10
20
30
40
50
60 Ψ-Zn0,8Mg0,2O
Δ-Zn0,8Mg0,2O
Energy (eV)
Ψ
(°
)
0
20
40
60
80
100
120
Δ (°)
Eg=3,36eV
1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5
0
10
20
30
40
50
60
70 Ψ-Zn0,6Mg0,4O
Δ-Zn0,6Mg0,4O
Energy (eV)
Ψ
(°
)
Eg=3,54eV 20
40
60
80
100
120
140Δ (°)
1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5
10
20
30
40
50
60
70 Ψ-Zn0,4Mg0,6O
Δ-Zn0,4Mg0,6O
Energy (eV)
Ψ
(°
)
0
20
40
60
80
100
120Δ (°)
1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5
20
25
30
35
40
45
50 Ψ-Zn0,2Mg0,8O
Δ-Zn0,2Mg0,8O
Energy (eV)
Ψ
(°
)
40
60
80
100
120
140Δ (°)
1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5
10
20
30
40
50
60
Δ
(°
) Ψ- MgO
Δ- MgO
Energy (eV)
Ψ
(°
)
20
40
60
80
100
120
140
160
Fig. 7. Ellipsometric spectra of Zn(1–x)MgxO thin films.
Transmittance and ellipsometric spectra were
recorded for optical study. The film porosity causes
diminution of the refractive index, which increases the
transmittance of the films in the transparent part of the
spectrum (Fig. 10). Reduction in the interferential
fringes amplitude, resulting from a lower refractive
index [26], maintains the transmittance at a higher level.
In contrast, in the absorption area, the transmittance is
lower after water etching. The optical confinement in the
pores and the multiple reflections caused by the textured
surface amplify the absorption effect decreasing the
transmitted light.
The ellipsometric spectra recorded before and after
etching (Fig. 11) show a clear difference. The
interferential fringes were shifted and had a greater
amplitude. An appropriate mathematical analysis [30] of
these spectra allows determining the refractive index
dispersion in the transparent area highlighting the etching
effect, as shown in Fig. 12. The ellipsometric results
confirm the diminution of the film refractive index
induced by the porosity resulting from the water etching.
0,0 0,2 0,4 0,6 0,8
3,1
3,2
3,3
3,4
3,5
3,6
3,7
Wurtzite phase
Eg
(e
V
)
Mg atomic ratio
From ellipsometry
From transmittance
Fig. 8. Band gap energy determinated from transmittance and
ellipsometric spectra.
Fig. 9. AFM 3D representation of Zn0.2Mg0.8O thin films
before and after etching in water.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 1. P. 55-63.
doi: https://doi.org/10.15407/spqeo20.01.055
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
61
200 400 600 800 1000 1200
0
20
40
60
80
100
Non etched Zn0,2Mg0,8O
Etched Zn0,2Mg0,8O
T
(%
)
Wavelength (nm)
Quartz
Fig. 10. Transmittance of Zn0.2Mg0.8O thin films before and
after etching in water.
1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5
10
20
30
40
50
60
Energy (eV)
Ψ
(°
)
20
40
60
80
100
120
140
160
Δ after etching
Ψ after etching
Δ
(°
)
Before etching
Fig. 11. Ellipsometric spectra of Zn0.2Mg0.8O thin films before
and after etching in water.
1,0 1,5 2,0 2,5 3,0 3,5 4,0
1,5
1,6
1,7
1,8
1,9
2,0
R
ef
ra
ct
iv
e
in
de
x
Energy (eV)
Non etched Zn0,2Mg0,8O
Etched Zn0,2Mg0,8O
Fig. 12. Refractive index of Zn0.2Mg0.8O thin films before and
after etching in water.
This study highlights the great technological
potential of Zn(1–x)MgxO nanoporous films, with tunable
band gap enabling several optoelectronic applications
[30], high transparency for photovoltaic applications
[31] and a large active surface essential for chemical
sensors [32] and photocatalysis [33].
4. Conclusion
Good quality Zn(1–x)MgxO thin films with tunable band
gap were deposited by simple spray pyrolysis method.
The transmittance maxima recorded on all films exceed
90%. An important increase of the band gap energy
(from 3.22 to 3.6 eV) is possible while maintaining the
wurtzite-like phase (for atomic ratio less than 0.4). If the
atomic ratio of Mg exceeds this value, two crystalline
phases (wurtzite and cubic) grow in competition
resulting in a compressive lattice strain. Therefore, finer
grains with a pronounced columnar growth are observed,
and the surface roughness decreases significantly. A
simple etching in water yields to nanoporous films, with
a great surface-to-volume ratio, a lower refractive index
and a better light transmission. These properties might
be interesting for various applications.
Acknowledgements
We would like to thank researchers and technicians of
LCAM-OEB and the Faculty of Chemistry (USTHB) for
their technical assistance in accomplishing this work.
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|
| id | nasplib_isofts_kiev_ua-123456789-214912 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1560-8034 |
| language | English |
| last_indexed | 2026-03-21T11:50:46Z |
| publishDate | 2017 |
| publisher | Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| record_format | dspace |
| spelling | Abdelhakim Mahdjoub Abdelaali Hafid Mohammed Salah Aida Abdelhamid Benhaya 2026-03-03T11:08:39Z 2017 An original way to obtain porous Zn₍₁₋ₓ₎MgₓO thin films by spray pyrolysis technique / Abdelhakim Mahdjoub, Abdelaali Hafid, Mohammed Salah Aida, Abdelhamid Benhaya // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2017. — Т. 20, № 1. — С. 55-63. — Бібліогр.: 35 назв. — англ. 1560-8034 PACS: 73.61.-r, 78.20.-e, 81.15.-z https://nasplib.isofts.kiev.ua/handle/123456789/214912 https://doi.org/10.15407/spqeo20.01.055 Zn₍₁₋ₓ₎MgₓO thin films with various concentrations of magnesium were deposited using the spray pyrolysis method. The transmittance spectra recorded for all films exhibit maxima exceeding 90%. The band gap energy of the films with wurtzite structure increases from 3.22 to 3.60 eV by incorporating Mg into ZnO. However, when the atomic ratio of Mg exceeded 0.4, a second crystalline phase (assigned to cubic MgO) became discernible in XRD patterns, a compressive strain was observed in the wurtzite lattice, and crystallite sizes decreased significantly. In accordance with these observations, finer grains with a pronounced columnar growth were observed in 3D AFM representations, and the surface roughness decreases significantly. Finally, selective etching in water yields porous films with a great surface-to-volume ratio, a lower refractive index, and a better light transmission. These porous films with tunable band gaps seem to be excellent candidates for various interesting applications. We would like to thank the researchers and technicians of LCAM-OEB and the Faculty of Chemistry (USTHB) for their technical assistance in accomplishing this work. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics An original way to obtain porous Zn₍₁₋ₓ₎MgₓO thin films by spray pyrolysis technique Article published earlier |
| spellingShingle | An original way to obtain porous Zn₍₁₋ₓ₎MgₓO thin films by spray pyrolysis technique Abdelhakim Mahdjoub Abdelaali Hafid Mohammed Salah Aida Abdelhamid Benhaya |
| title | An original way to obtain porous Zn₍₁₋ₓ₎MgₓO thin films by spray pyrolysis technique |
| title_full | An original way to obtain porous Zn₍₁₋ₓ₎MgₓO thin films by spray pyrolysis technique |
| title_fullStr | An original way to obtain porous Zn₍₁₋ₓ₎MgₓO thin films by spray pyrolysis technique |
| title_full_unstemmed | An original way to obtain porous Zn₍₁₋ₓ₎MgₓO thin films by spray pyrolysis technique |
| title_short | An original way to obtain porous Zn₍₁₋ₓ₎MgₓO thin films by spray pyrolysis technique |
| title_sort | original way to obtain porous zn₍₁₋ₓ₎mgₓo thin films by spray pyrolysis technique |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/214912 |
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