Structural, optical and electrical properties of the Zn doped MoO3 deposited on porous silicon

Accepted Manuscript
Title: Structural, optical and electrical properties of the Zn
doped MoO3 deposited on porous silicon
Authors: Taher Ghrib, Amal L. Al-Otaibi, Mody Alqahtani,
Nafla A Altamimi, Afrah Bardaoui, Sami Brini
PII:
DOI:
Article Number:
S0924-4247(19)30857-X
https://doi.org/10.1016/j.sna.2019.111537
111537
Reference:
SNA 111537
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Sensors and Actuators A
Received date:
Revised date:
Accepted date:
15 May 2019
31 July 2019
2 August 2019
Please cite this article as: Ghrib T, Al-Otaibi AL, Alqahtani M, Altamimi NA,
Bardaoui A, Brini S, Structural, optical and electrical properties of the Zn doped
MoO3 deposited on porous silicon, Sensors and amp; Actuators: A. Physical (2019),
https://doi.org/10.1016/j.sna.2019.111537
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Structural, optical and electrical properties of the Zn doped MoO3 deposited
on porous silicon
Taher Ghrib1,2,*, Amal L. Al-Otaibi1,2, Mody Alqahtani1,2, Nafla A, Altamimi1, 2, Afrah Bardaoui3, Sami
Brini1,2
1
of
Department of physics, College of Science, Imam Abdulrahman Bin Faisal University, P.O. Box 1982,
31441, City Dammam, Saudi Arabia.
2
Basic and Applied Scientific Research Center, Imam Abdulrahman Bin Faisal
University, P.O. Box 1982, 31441, Dammam, Saudi Arabia.
3
Laboratory of Nanomaterials and Systems of Renewable Energy (LANSER), Center for Research and
Technologies of Energy, BorjCedria Technopole, Bp 95, Hammam-Lif, 2050 Tunis, Tunisia
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* Corresponding author: [email protected]
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Highlights:
In this work it was studied and presented the 5% zinc doped molybdenum oxide deposited on
porous silicon prepared with different porous density by varying the etching duration (at 3, 5, 7,
10,12 min), it was denoted:

Successful deposition of Zn doped MoO3 films on porous silicon

Zn doped MoO3 films are predominantly amorphous in structure with small fraction of
orthorhombic MoO3 will crystallized progressively with the etching time.
High photocalytic effect of 5%Zn doped MoO3 nanofilm.
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
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Abstract:
This study presents the preparation process of porous silicon substrates and the deposed
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thin film of 5%Zn doped MoO3 on porous silicon. The first part covers many techniques used
to characterize porous silicon substrates. It examines the photoluminescence spectra analysis to
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study the etching time effect on the PL intensity, and the UV–vis analysis to find the band gap
of the prepared porous silicon substrates with different etching time. The second part treats
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several techniques for studying the etching time effect on the structural, electrical, optical
properties of the 5%Zn doped MoO3 thin film. X-ray diffraction (XRD) was used to study the
structure of the samples, Fourier transform infrared spectroscopy (FTIR) was used to determine
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the functional groups. While Photoluminescence spectra analysis, Photocatalytic activity test,
and Electrochemical impedance spectroscopy (EIS) were used to study the electrical properties.
By increasing the time etching, the structure crystallization was ameliorated, the band gap was
decreased from 2.96 to 2.75 eV, a visible optical absorption was detected at 450 to 500nm range
which increased from 88 to 92% and the electrical conductivity was increased by ten times from
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6.28 × 10−5 to 6.06 × 10−4 −1 . cm−1 .
Keywords: Molybdenum oxide; Zinc doping; etching time; photocatalysis; electrochemical
impedance spectroscopy.
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1. Introduction
Semiconductor metal oxides such as MoO3, SnO2, ZnO, In2O3, ... have been widely
studied for their high thermal and chemical stability and suitability in many applications.
Molybdenum trioxide belongs to the transition metal oxides, crystallizes in the orthorhombic
structure and has high chemical and thermal stability and interesting physical properties that
may be useful in optoelectronic apparatus. Recently, due its attractive electrical properties, the
MoO3 oxide was used in many applications such as optical devices [1] , smart windows [2],
medicine and agriculture [3] and it was incorporated in transistors [4], catalysts [5],
electrochemical capacitors [6] and gas sensors [7-9] to improve their physical properties.
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Molybdenum trioxide can be crystallized in three polymorphic phases; the stable phase α-MoO3
and two meta-stable phases β-MoO3 and h-MoO3. Also, it used different elements for the
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doping of MoO3 such as iron used by Ouyang et al. [8] who studied the facile synthesis of Fedoped MoO3 by a hydrothermal method, in which the Fe doping amount was easily adjusted to
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be 0.3, 0.6, 0.7 and 0.9 wt.% by only increasing the reaction time. Kamoun et al.[10]
investigated the physical properties of MoO3 in thin films doped with europium element and an
aqueous solution of ammonium Molybdate containing various concentration of Europium (0–
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2%) sprayed on a glass substrate heated at 460 °C in air. Other researchers used the Cobalt [11]
, the cerium [12],… as dopant to ameliorate its physical properties.
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The MoO3 were mainly manufactured in thin films shape by using chemical or physical
methods. The physical methods include magnetron sputtering [13] and pulsed laser deposition
(PLD) [14], while the chemical methods include spay pyrolysis [15], chemical vapor deposition
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(CVD) [16] and electrochemical deposition methods [17, 18]. These processes are very simple
and can be operated at relatively low deposition temperature using relatively low concentrations
and gave thin films in good adhesion with the substrate; demonstrating a uniform molecular
distribution, excellent optical properties and high purity. The nature of the used wafer on the
creation and the grains’ shape constituting the prepared thin film and its overall physical
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properties such as the glass [12, 14], porous silicon [2, 19] and graphite [20].
This work examined the thin film of MoO3 deposited on porous silicon; which was
prepared in various etching times. The prepared MoO3 thin films deposited on porous silicon
were studied using the X-ray diffraction (XRD) to investigate the evolution of its structure, the
scanning electron microscopy (SEM) to investigate its morphology, the UV–vis spectra and
photoluminescence measurements in order to analyze the optical properties and measure the
band gap, the Fourier transform infrared spectroscopy (FTIR) to analyze the existing functional
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groups and its purity and the Electrochemical impedance spectroscopy (EIS) and Hall effect to
study the evolution of its electrical properties. The photocatalytic effect of the zinc doped
MoO3 deposited on porous silicon substrate on methylene blue (MB) was examinated and the
obtained results were related to the optical and electrical properties behaviors.
2. Porous silicon substrate.
2.1. Preparation
The used substrate as initial specimen was n-type Si with orientation (100). The Si
specimen was cleaned in two steps. Firstly, by using an ethanol to remove the oxide layer from
its surface. The second step was by using the HCl (10%) for 5 min to remove mineral
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impurities. Thin homogenous Porous silicon (PSi) layers of different thicknesses were formed
on the front surface of the substance using electrochemical (EC) method. Fig. 1 shows EC
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system, in this case the n-type silicon substrate surface emerged in a solution constituted of
hydrofluoric acid and ethanol (1:1, 20% diluted). One face of the silicon wafer was in contact
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with aluminum anode plate and the other side with an electrolyte which plunged a platinum
electrode (cathode) by using a current intensity of 10 mA by 3, 5, 7, 10, 12 min at room
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temperature.
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Fig. 1.
2.2. Photoluminescence spectra analysis
Fig. 2 offers the variation of photoluminescence spectra at room temperature using 340
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nm wavelength excitation, with etching duration for the porous silicon (PSi) specimens obtained
at the current densities 10 mA/cm2 at 3, 5, 7, 10, 12 min. The peak of the intensity shifted to the
left (blue range) and the maximum wavelength increased from 472.97 to 494.39 nm when
increasing the etching duration. It is denoted that the PL intensity increased with the etching
duration and then with the porosity density it became higher for the highest etching duration (12
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min). These results are in good agreement with Omar et al.[2] who studied the effects of
electrochemical etching time on the performance of porous silicon solar cells on crystalline ntype (100) and (111). This increase of the photoluminescence intensity may be influenced by
the increase in the total volume of the nano-pores and the surface of the porous silicon. Also,
the blue shift of PL spectra, as shown in fig. 2, may be attributed to the quantum confinement
effect between electrons in the conduction band and the holes in the valence band. The
confinement number increases with photons number trapped inside the porous silicon. This
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trapping of photons will increase with density and the volume of the generated pores. The
variation PL spectra confirm that the specimens have a different porous layer and pore diameter.
Because when the etching duration increases, the pores size increases and the Pl intensity will
decrease; but in our case, it increased. This increase may be interpreted by the apparition of new
pores inside the first created pores. Therefore, the increase in the etching time is attributed to the
apparition of pores with double wells whose inside is of nano-size and favors charge carrier
quantum confinement. The probability of recombination of e and h is higher in very small
structures (quantum confinement effects), leading to higher emissions. The pores quantum
dimensions of the structure in the sample favorites the PL shift towards shorter wavelengths.
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The interfacial complexes in the form of non-bridging oxygen hole centers are also possible
sources of PL in PSi such as Si-O coming from the oxidation of the surface atoms. The FWHM
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of the photoluminescence maximum decreased when the etching time increased as indicated in
table 1. The width of the photoluminescence peak is a good indicator of material quality,
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because the photoluminescence peak may easily be broadened by structural defects or
impurities.
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Fig. 2. and Table 1.
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2.3. UV–vis analysis
Fig. 3 shows the optical absorption of the Psi n-type (100) samples prepared under current
density 10 mA/cm2, with different etching times 3, 5, 7, 10 and 12min. UV-vis reflectance
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spectra of Psi substrates prepared are measured in the range of 400-800 nm. It is denoted that
there was a small increase in the optical absorption when the etching time increased. The
increase in the optical absorption can be interpreted by the confinement and trapping of photons
inside the pores and after a multi-reflection which minimizes their optical reflection by the PSi
material, and they will be absorbed. The highest effective absorption of the PS layer was
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recorded at 12 min etching duration, which clearly reduced light reflection and increased lighttrapping at wavelengths ranging from 400 to 1000 nm, compared with the non-etched Si sample
and the other etched samples.
Fig. 3.
It is well-known that the silicon is an indirect transition semiconductor, the absorption
coefficient and the band gap energy Eg are related by the Tauc relationship[21](αhυ)2=A(hυEg), where hυ is the photons excitation energy. In fig.4, the band gaps (Eg) values are found to
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be increased in all samples and their values are 2.091, 2.095, 2.104, 2.109 and 2.131 eV
respectively for 3, 5, 7, 10, 12 min etching time as presented in table 1. It is denoted from these
Eg values that the band gap increases versus the etching process out of the increase in the pores
density and volume leading the Si wafer to an insulator behavior due to the vacuum created
inside. These results are in good agreement with some other works. Hussein et al.[19], for
instance, studied the effect of current density and etching time on photoluminescence and
energy band gap of p-type porous silicon. Also Douri et al.[22] examined the Etching time
affect on optical properties of porous silicon for solar cells fabrication. It fits the absorption
curve between 1and 2.4 eV with this formula and estimates the energy gap Eg.
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Fig. 4.
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3. Properties of 5% Zn doped MoO3thin film deposited on porous silicon
3.1. Preparations procedures
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At first, MoO3 in powder shape was prepared by a hydrothermal method [23]. Ammonium
heptamolybdate tetrahydrate (AHM; (NH4)6Mo7O24·4H2O), and nitric acid (HNO3) were used
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as precursors. The AHM was dropped gradually in 30 ml distilled water under uniform stirring
at room temperature until the saturation. The resulting solution was acidified with nitric acid
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(2.2 M) to a total volume of 70 ml, made in a stainless steel autoclave and heated for 40 hours at
180 ° C. The precipitate was washed with deionized water several times and dried in the oven
ref-K. SI. 1700 S for 7h at 70°C. The dried product of yellowish color was calcined for 5 h at
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600°C giving a fine MoO3 powder.
Secondly , to get 5% Zn doped MoO3, the zinc nitrate (Zn(NO3)2·6H2O) powder was added to
previously prepared powder (MoO3 pure) in appropriate fractions to obtain a final solid solution
of 1:20 portions (5 wt. % Zn and 95 wt. % MoO3) denoted Z5M. After that, the mixture was
grinded in an agate mortar and transferred into a 50 mL stainless steel autoclave for 25 h at
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200°C. After being washed repeatedly with distilled water, the obtained white powder was dried
for 12 h at 80°C.
Finally the Z5M powder was dissolved in a hydrogen peroxide (H2O2) solution. Then, it
was spread on a well cleaned PSi substrate (2×2cm size), which was placed on the substrate
holder of a spin coating unit and spun at 2000 rpm. The coated MoO3 films of 200 nm thickness
deposited on different etched silicon substrates were annealed from 900 °C for 1h and
characterized by the following analysis.
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3.2. X-ray diffraction analysis
X-ray diffraction (XRD) patterns of the prepared samples were depicted from 10° to 80°
with an incident X-ray angle 2° and evaluated according to JCPDS card No. 0050508. Fig. 5-a
gives the XRD patterns for all samples at an incident angle of 2ᵒ with two broad diffraction
peaks at around 2=22ᵒ and 62ᵒ angles corresponding to (110) and (430) respectively. These are
related to the orthorhombic structure implying that the Zn doped MoO3 deposited on PSi starts
with an amorphous structure and tends progressively towards a crystalline structure of
orthorhombic -MoO3 phase. Fig. 5-b shows the SEM image of the Zn doped MoO3 deposited
on porous Si etched at 10 min which demonstrates randomly distributed pores on the surface
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filled with the film with various sizes ranging from about 60 nm to 85 nm.
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Fig. 5
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3.3. FTIR Analysis
Fig. 6 shows the Fourier transform infrared (FTIR) spectrum of MoO3 deposited on
porous silicon measured in the range of 400–3000 cm-1. The spectrum offers two peaks at 809
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cm−1 assigned to the stretching mode of oxygen in Mo–O–Mo bonds inter-molecular and 1092
cm−1 assigned to the terminal Mo=O stretching intra-molecular vibration [24, 25]. These two
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peaks correspond to a layered orthorhombic α-MoO3 phase in accordance with the result
obtained with the XRD study. Also, it shows a broad peak at 1208 cm−1conforming to the
bending vibration of Si–O–Si asymmetric stretching modes of a SiO2 [26] thin film formed on
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the porous silicon surface after etching. Also, 2254 cm-1 belongs to the residual of CO2 present
in the surrounding air [27]. The peak obtained at 470 cm−1 provides the Zn-O finger print related
to the stretching vibration in the MoO3 structure [27]. This general form of these curves
indicates no formation of new bonds or apparition of alternative contamination after deposition
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on the silicon wafers.
Fig. 6
3.4. Photoluminescence spectra analysis
Usually the origin of photoluminescence (PL) can be attributed to four facts which are the
nano-crystals surface states, the quantum confinement, the specific defects and the phase
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disorder in structures. Related to these facts, the surface and interfacial properties can also
influence it. The prepared materials revealed an amorphous phase, and this means in practice
that the quantum size effect does not play the crucial role in PL properties of the prepared
samples. But the morphology of the quantum pores on the silicon has a slight effect on PL
active structures. Photoluminescence spectra of MoO3 deposition on porous silicon are shown in
fig. 7 in the 200–700 nm range. Four samples with silicon etched at 3min, 5min, 7min, and
10min show two emission peaks in photoluminescence spectra centered at 310 and 380 nm
while the sample with silicon substrate etched for 12min present another peak centered at 420
nm. The two peaks, 380 nm and 420 nm, can be attributed to the blue emission which gives to
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the samples etched at 12 min and seems to be the best one for the luminescence in a visible
range [28]. The origin of this major difference in the observed PL intensity is related to the
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difference in temperature and etching time. These emissions can be related to band transitions
due to the presence of Mo, O and Zn interstitial sites as well as the surface defects which are
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correlated to the density of defaults. These results are useful for the development of advanced
optoelectronic and nano devices based on a wide band gap luminescent metal oxide like MoO3.
Future work will be focused on the wavelength dependent emission properties MoO3 and to see
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the possibilities to enhance the visible emission.
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Fig. 7
3.5. Photocatalytic activity test
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Fig. 8 shows the UV-vis absorption spectra of the MB solution at the same reaction time
1h for all samples MoO3/porous silicon catalyst. The MB solution is constituted of an MB
powder dissolved in hydrogen peroxide solvent. This figure shows the variation of the optical
absorption of the methyl blue (MB) after its degradation with the prepared samples. The
photocatalytic activity of the samples was evaluated by the degradation of MB solution under a
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visible light irradiation [29, 30]. It exhibits the UV–vis absorption spectroscopy recording the
absorption behavior of the solution after treatment by comparing it with the characteristic light
absorption of MB. Initially, the maximum absorption peak of MB is located at 667 nm,
accompanied by a shoulder peak at 618 nm [31]. It is obvious that both absorption peaks have
not shifted with the etching time but just subjected a decreasing in their intensities, indicating
that MB has been effectively degraded. Also, it is brightly seen that the intensity of
characteristic peak for MB remarkably decreases with treatment at 3 min and reaches about zero
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after 12 min etching time, suggesting the high photocalytic effect of the 5%Zn doped MoO3
nanofilm.
Fig. 8
3.6. UV–vis analysis
Fig.9 shows the absorbance spectra of MoO3 deposited on PSi for five different etching
times at 3, 5, 7, 10 and 12 min at a heat treatment of 900ᵒC. UV-vis spectra of these prepared
samples are measured in the range of 300-1000 nm. It is denoted that there was an overall
decrease in the optical absorption with the wavelength for all the etching times and pass by one
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maximum absorption in the range centered at about 330nm and another broad peak at the visible
range centered at 450 to 500nm. Also, there was an increase in the optical absorption with the
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etching time which can be attributed to the enhancement in the pores volume and density;
which can fill more material of MoO3:Zn and increase the absorption of the photons trapped
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inside. In fig.10, (αhν)2 was plotted as a function of photon energy (hν). For various etching
times, it is denoted that the band gap value is affected by the etching time. From 3 min to 12
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min, the band gap increases 2.78, 2.96, 2.90, 2.84, 2.75eV respectively which are summarized
in table 2.
3.7. Electrical properties.
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Fig. 9 and Fig. 10
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Electrochemical impedance spectroscopy (EIS) is a nondestructive technique that can study
the chemical and physical properties in solids. Also, it can study the electrical properties of
materials. The results of the impedance measurement can be presented by the complex plane
plot of the opposite of the imaginary part - Z" versus the real part Z' of the complex impedance
Z. Each point on the complex plane plot represents the impedance at a certain frequency [32].
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For the Nyquist plot as obtained from the prepared specimen in fig. 11, the equivalent
impedance of these elements may be arranged in parallel or in series. Through the Nyquist
form, when it takes a semicircle, the equivalent circuit can be constituted of two elements; one
resistor (R1) in series with another element constituted of resistor (R2) in parallel with capacitor
C1 as shown in Fig. 11 [33]. R1 is an ohmic resistance obtained at a high frequency; which is
related to deposited thin film (5%Zn doped MoO3) and R2 is the diameter of the semicircle
which indicates the interfacial resistance between the thin film and the porous silicon substrate.
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Fig. 11
The total equivalent impedance in series is given by the sum of the impedance values of
each individual element:
𝑍𝑒𝑞 = 𝑅1 + 𝑍𝑅2 ||𝐶1
In parallel circuit, the impedance is given by the reverse of the impedance fraction sum for each
element:
1
𝑍𝑅2 𝐶1
=
1
𝑅2
+
1
𝑍𝐶1
1
Where 𝑍𝐶 1= 𝑗𝐶 is the capacitor impedance and j the imaginary number defined as j2=-1, ω is
1
1
𝑅2
𝑍𝑅2𝐶 =
+ 𝑗𝐶1 =
1+𝑗𝑅2 𝐶1 
𝑅2
𝑅2
1+𝑗𝑅2 𝐶1 
𝑅2 (1−𝑗𝑅2 𝐶1 )
1+(𝑅2 𝐶1 )2
= 𝑅1 +
𝑅2
1+(𝑅2 𝐶1 )
−𝑗
2
𝑅22 𝐶1 
1+(𝑅2 𝐶1 )2
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= 𝑅1 +
𝑅2
1 + 𝑗𝑅2 𝐶1 
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𝑍𝑒𝑞 = 𝑅1 +
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𝑍 𝑅2 𝐶
=
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1
of
angular frequency.
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= 𝑍 ′ + 𝑗 Z''
It can be denoted that, at high frequencies, the second and third terms in the fraction will
go to zero and only 𝑅1 is observed. When the frequency is decreased even further the
denominator will go to a value of one, because 𝑅2 𝐶1  tends to zero and the imaginary part will
be infinitely small; only R1+R2 will then be observed. At a medium frequency the peak of the
semicircle will be observed when the value for the frequency is equal to 1/𝑅2 𝐶1 ; then the total
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impedance will be:
𝑍𝑒𝑞 = 𝑅1 +
𝑅2
𝑅2
−𝑗
2
2
The Nequist impedance spectra of MoO3/PSi under darkness are shown in fig.12. These spectra
are characterized by a semicircular shape. The radius of these semicircles and the resulting
resistance show an etching time dependency; it decreases when the etching time is increasing
(from 3 min to 12 min); leading to the improvement in the electrical properties of the prepared
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material [34]. The decrease in the curvature radius estimates the evolution of the effective
electron lifetime, the effective electron chemical diffusion coefficient and the effective electron
diffusion length and mobility in the prepared thin film; which gives the material the electrical
properties that lead to a high photovoltaic efficiency. The decrease in the semicircle radius
implies a decrease in the electron lifetime leading to a decrease in the volume charge Nb and
surface charge Ns densities in the conduction band; which can vanish the overall photovoltaic
efficiency. The decrease in the electron lifetime appears clearly in the PL measurement of fig. 7
which increases due to the charge recombination of the electron lifetime. Also, the decrease in
the curative radius is accompanied by a decrease in the resistance R1and the resistance R2;
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which facilitates the electron migration from the thin film to the silicon substrate and diminishes
the lifetime.
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Fig. 12
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These results are in good agreement with those obtained by Hall Effect measurement
summarized in table 2; which clearly shows a decrease in the volume and surface charge
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densities with the etching time and an increase in the charge mobility µ and the electrical
Table 2
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Conclusion
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conductivity σ. These materials can be used with good performance in photovoltaic cells.
This work studied the effect of deposition 5%Zn doped MoO3 on porous silicon etched
with various times on the evolution of their electrical, optical and structural properties. It was
observed that the porous silicon substrates have a band gap from 1.5 to 1.6 eV which increases
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versus the etching time. Also, it was denoted that the PL intensity increases with the etching
duration. For the study of the etching time effect on the electrical, structural, optical properties
of the 5% Zn doped MoO3 thin film; it used the XRD which shows that the sample present
amorphous structure will be crystallized for the highest etching time giving an orthorhombic
phase. PL spectra show two emission peaks centered respectively at 310 and 380 nm; which are
attributed to UV and blue emissions, the band gap energy decreases from 2.96 to 2.75 eV. The
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etching time improves strongly the photocatalytic effect towards the methyl blue and the
electrical properties.
Acknowledgements
The authors gratefully acknowledge use of the services and facilities of the Basic and
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Applied Scientific Research Center at Imam Abdulrahman Bin Faisal University.
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14
Author Biography
Taher Hcine Ghrib is currently an associate
professor and aggregated teacher in physic, at the College of
Sciences of Dammam of Imam Abdul Rahman bin Faisal
University-Saudi Arabia. He obtained his habilitation in
Physics at the science college of Carthage-UniversityTunisia on 2017. He prepared his thesis in Tunisia that
of
covers “investigation of the thermally treated steel by the
Photothermal Deflection Technique” and presented on 2008. He obtained his aggregation in
ro
Physics and Chemistry at the preparatory institute for scientific and technical studies of El
Marsa on 2001 of Tunisia. He worked as a course teacher of physics. He worked on steel and
-p
metal alloys in his thesis; he demonstrated a very practical method for measuring the
mechanical properties of steels such as hardness by measuring the thermal conductivity by
means of mathematical models and experimental nondestructive measurements. Almost all of
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his work is published in numerous publications in various journals and books.
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Now he is specialized in nano and porous materials and thin films of metals, perovskites and
alloys. He is involved in the project ETRERA (Empowering Tunisian Renewable Energy
Research Activities) which object is to realize a fuel cell of high electrical performance and he
ur
na
has led many scientific projects in Saudi Arabia. And he is the principle investigator of the
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nanomaterials technology unit.
15
Figure captions
Fig. 1. Schematic diagram of the porous silicon anodization circuit.
Fig. 2. Variation of photoluminescence peaks for porous silicon specimens prepared under
current density 10 mA/cm2, with different etching time 3, 5, 7, 10 and 12 min.
Fig. 3. Solid state UV–vis spectrum of porous silicon at 3, 5, 7, 10, 12 min under current density
10 mA/cm2.
of
Fig. 4. Band gap of PSi samples prepared under current density 10 mA/cm2, with different
ro
etching time 3, 5, 7, 10 and 12 min.
Fig. 5. XRD patterns of 5%Zn doped MoO3 deposited on n-type porous silicon prepared under
of the obtained specimen for 10min etching time.
-p
current density 10 mA/cm2, with different etching time 3, 5, 7, 10 and 12 min and SEM image
10, 12 min and annealed at 900 ᵒC.
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Fig. 6. FTIR absorbance of 5%Zn doped MoO3 deposited on porous silicon etched at 3, 5, 7,
min and annealed at 900 ᵒC.
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Fig. 7. PL spectra of 5%Zn doped MoO3 deposited on porous silicon etched at 3, 5, 7, 10, 12
Fig. 8. UV-vis absorption spectra of MB solution over 5%Zn doped MoO3 on porous silicon
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etched at 3, 5, 7, 10, 12 min and annealed at 900 ᵒC.
Fig. 9. Optical absorbance of 5%Zn doped MoO3 deposited on porous silicon wafers prepared
under current density 10 mA/cm2, with different etching time 3, 5, 7, 10 and 12 min and
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annealed at 900 ᵒC.
Fig. 10. Tauc plots of the specimens 5%Zn doped MoO3 deposited on Psi wafers prepared with
different etching time 3, 5, 7, 10 and 12 min and annealed at 900 ᵒC.
Fig. 11. Equivalent circuit model employed in analysis of electrochemical impedance data for
the 5%Zn doped MoO3 deposited on porous silicon and annealed at 900 ᵒC.
Fig. 12. The Nequist impedance spectra of 5%Zn doped MoO3 deposited on Psi wafers etched
at 3, 5, 7, 10 and 12 min and annealed at 900 ᵒC, under darkness at room temperature.
16
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-p
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Fig. 1.
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Figures list:
17
9
8
3 min
5 min
7 min
10 min
12 min
7
of
6
5
ro
4
3
-p
2
1
0
-1
500
700
600
wavelength(nm)
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400
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photoluminescence intensity (a.u)
10
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Fig. 2.
18
800
900
0.90
0.80
0.75
0.60
0.55
400
3min
5min
7min
10 m i n
12 m i n
500
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0.65
of
0.70
-p
Absorbance (a.u.)
0.85
600
700
800
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wavelength (nm)
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Fig. 3.
19
900
1000
14
12
10
(h ev)

3min
5min
7min
10min
15min

8
6
of
4
0
0.5
1.0
1.5
2.0
2.5
3.0
4.0
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Fig. 4.
3.5
-p
hev)
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2
70
60
ity (a.u.)
50
40
(110)
3 min
5 min
7 min
10 min
12 min
(b)
(a)
(430)
20
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-p
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Fig. 5.
21
2.5
1092
3 min
5 min
7 min
10 min
12 min
Absorbance (a.u.)
2.0
1.5
1208
470
2341
809
1.0
0.5
500
1000
1500
2000
2500
3000
3500
4000
-1
ro
Wavenumber (cm )
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-p
Fig. 6.
22
of
0.0
600
3 min
5 min
7 min
10 min
12 min
300
of
Pl intensity(a.u.)
900
0
200
400
600
Jo
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Fig. 7.
23
800
-p
Wave lenght(nm)
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0
MB
3 min
5 min
7 min
10 m i n
12 m i n
0.2
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absorption
0.4
500
550
600
650
700
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Fig. 8.
24
750
-p
n m)
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0.0
800
0.90
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3 min
5 min
7 min
10 min
12 min
0.85
0.80
300
400
500
600
700
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Fig. 9.
25
800
-p
Wavelength (nm)
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Absorbance (a.u.)
0.95
900
24
22
20
18
14
10
3 min
5 min
7 min
10 min
12 min
8
6
4
2
0
3
4
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heV)
-p
2
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Fig. 10.
26
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12
ro
2
hu) (eV)
2
16
5
Equivalent circuit
Nyquist plot
2000000
room temperature
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Z,,(Ohm)
3000000
min
min
min
min
min
-p
4000000
3
5
7
10
12
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5000000
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Fig. 11.
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1000000
0
Jo
0
2000000 4000000 6000000 8000000
,
Z (Ohm)
Fig. 12.
27
Table captions
Table 1. Show the FWHM of photoluminescence peaks with different etching time 3, 5, 7, 10 and 12
min.
Table 1.
PSi Band Gap
FWHM from Pl
3 min
2.091
0.663
5 min
2.095
0.633
7 min
2.104
0.607
10 min
2.109
0.557
12 min
2.131
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Etching time
-p
0.500
Table 2.
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3, 5, 7, 10 and 12 min and annealed at 900ᵒC.
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Table 2. Electrical properties of5%Zn doped MoO3 deposited on porous silicon at different etching time
NS [/cm2]
µ[cm2/Vs]
σ[/Ohm.cm]
Band Gap [ eV ]
−1.460 × 1014
−5.839 × 109
2.685
6.279 × 10−5
2.78
Z5M/PSi5
−1.267 × 1013
−5.066 × 108
1.285 × 102
2.607 × 10−4
2.96
Z5M/PSi7
−7.977 × 1013
−4.387 × 109
2.964 × 102
3.788 × 10−4
2.90
Z5M/PSi10
−2.275 × 1012
−1.138 × 108
1.493 × 103
5.444 × 10−4
2.84
Z5M/PSi12
−1.239 × 1012
−6.194 × 107
3.052 × 103
6.057 × 10−4
2.75
Nb [/cm3]
Z5M/PSi3
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Sample
28