Effect of Spin Coating Parameters on Optical and I–V Characteristics of Fe2O3 Thin Films
Niranjan S. Samudre1, Bharat G.
Thakare1, Navnath M. Yajgar1, Amol R. Naikda1,
Bhushan B. Chaudhari1, Sudam D. Chavhan1*, R. R. Ahire1,
Sachin J. Nandre2*,
1
Department of Physics, S. G. Patil Art’s, Science and Commerce College, Sakri
(Maharashtra)
2
Department of Physics, U. P. College, Dahivel (Maharashtra)
*Email:
- sachinjnandre@gmail.com ,sudam1578@gmail.com
Abstract
Iron oxide (Fe2O3)
thin films were successfully prepared on glass substrates using a simple and
cost-effective spin coating technique to study the influence of spin speed on
their optical and electrical properties. A 0.5 M ferric chloride (FeCl3)
precursor solution was used for deposition, and films were coated at 2500 rpm
and 3000 rpm for 60 s. The deposited films were annealed at 600 °C for 5 h to
obtain the crystalline hematite (α- Fe2O3)
phase with improved structural stability. Optical properties were analysed
using UV–Visible spectroscopy, which revealed strong absorption in the visible
region along with good transparency at longer wavelengths. The optical band
gap, estimated from Tauc plots, was found to range between 1.84 and 1.90 eV,
indicating that spin speed influences film thickness and microstructural
uniformity. Electrical characterization was carried out through current–voltage
(I–V) measurements in the voltage range of 0–14 V at room temperature. The
films exhibited semiconducting behaviour with nearly ohmic conduction at lower
voltages. The film deposited at 3000 rpm showed higher current and lower
resistance compared to the 2500 rpm film, suggesting enhanced crystallinity and
improved charge carrier mobility. These findings confirm the significant role
of spin coating parameters in tailoring Fe2O3 thin
films for optoelectronic and energy-related applications.
Keywords: -
Fe2O3 thin films, Spin coating, Optical band gap, I–V characteristics,
Hematite, Optoelectronic applications, Photovoltaics.
1. Introduction
Iron oxide (Fe2O3)
thin films have emerged as promising materials for optoelectronic and energy
applications due to their earth abundance, non-toxicity, and suitable bandgap
(~2–2.2 eV) for solar energy conversion (1,2). Among deposition techniques,
spin coating is widely recognized as a cost-effective and versatile method for
producing uniform thin films with controlled thickness and morphology (3,4).
The performance of Fe2O3thin films is strongly influenced
by spin coating parameters such as spin speed, precursor concentration, solvent
composition, and annealing temperature, which govern film thickness,
crystallinity, and surface roughness (5–7). These structural modifications
directly affect optical properties including absorption edge, bandgap energy, and
refractive index (8,9), as well as electrical transport behaviour such as
leakage current and resistive switching (10–12). Recent studies have
demonstrated that tuning spin speed and annealing conditions can significantly
enhance charge carrier mobility and optical transparency, thereby improving
device performance in photoelectrochemical cells and sensors (13,14).
Furthermore, solvent composition and precursor concentration have been shown to
alter defect states and bandgap values, enabling bandgap engineering for
tailored optoelectronic applications (7,15). Surface morphology control through
optimized spin parameters also plays a critical role in determining I-V
characteristics and stability of Fe2O3thin films (16,17).
Consequently, understanding the correlation between spin coating parameters and
the resulting optical and electrical properties is essential for advancing Fe2O3-based
devices in photovoltaics, gas sensing, and resistive switching technologies
(18–20).
2. Materials and Methods
2.1 Materials
Ferric chloride (FeCl3,
extra pure 97%) was used as the precursor material. Analytical grade ammonia
solution was employed to adjust the pH-03 of the precursor solution. Double
distilled (DD) water was used as the solvent medium to ensure purity and
minimize contamination during film preparation.
2.2 Preparation of Precursor Solution
A 0.5 M solution of ferric chloride was prepared by
dissolving 0.675g of FeCl3 in 5 mL of double distilled water.
Ammonia was added dropwise under continuous stirring until a homogeneous
solution was obtained. The solution was filtered to remove any undissolved
particulates and stored in airtight containers prior to deposition.
2.3 Substrate Cleaning
Glass substrates were
ultrasonically cleaned sequentially in acetone, ethanol, and double distilled
water for 10 minutes each, followed by drying in ambient air. This cleaning
procedure ensured removal of organic and inorganic contaminants, thereby improving
film adhesion and uniformity.
Figure
1 Formation of Fe2O3 Thin Films by Spin Coating
Method
2.4 Spin Coating Deposition
The prepared precursor solution was dispensed onto the
centre of the substrate mounted on the spin coater chuck. Spin coating was
performed at two different speeds: 2500 rpm and 3000 rpm, each for a duration
of 60 seconds. During spinning, centrifugal force spread the solution uniformly
across the substrate, while solvent evaporation occurred simultaneously,
forming a thin liquid film.
2.5 Annealing Treatment
After deposition, the coated substrates were dried at
100 °C for 10 minutes to remove residual solvent. Subsequently, the films were
annealed at 600 °C for 5 hours in a muffle furnace to induce crystallization of
the hematite (α- Fe2O3) phase. Annealing at this
temperature was chosen to enhance crystallinity, grain growth, and stability,
which are critical for optical and electrical studies.
3. Results and Discussion
3.1 Optical Properties
Fe2O3 thin films were
successfully deposited on glass substrates using the spin coating technique,
with constant spin speed, varied between 2500–3000 rpm. UV–Vis. spectroscopy
revealed strong absorption in the visible region, accompanied by good
transparency at longer wavelengths. The optical band gap, determined using
Tauc’s relation, was found to range between 1.84–1.90 eV. This variation is
attributed to differences in film thickness and microstructural uniformity
induced by changes in spin speed. These findings highlight the critical role of
deposition parameters in tailoring the optical response of Fe2O3
thin films.
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a)
b)
Figure
2 a) UV-Visible absorption spectra of Fe2O3 thin
films, b) Tauc plot Vs photon energy (hv) of Fe2O3.
3.2 Electrical Properties
The current–voltage (I–V) characteristics of Fe2O3
thin films deposited by the spin coating method at 2500 RPM and 3000 RPM
with a constant spin time of 60 second were investigated to evaluate their
electrical conductivity behaviour. The measurements were carried out in the
voltage range of 0–14 V at room temperature.
Both films exhibit a continuous increase in current
with increasing applied voltage, confirming the semiconducting nature of the Fe2O3
thin films. The nearly linear trend at lower voltages indicates ohmic
conduction behaviour, suggesting good electrical contact between the electrodes
and the film surface. However, a comparatively higher current response is
observed in the film deposited at 3000 RPM.
Figure
3 Current–voltage (I–V) characteristics of Fe₂O₃ thin films.
At 14 V, the 3000 RPM film shows significantly higher
current than the 2500 RPM film, indicating lower electrical resistance and
enhanced charge carrier transport. The improvement in conductivity with
increasing spin speed can be attributed to better film uniformity, reduced
grain boundary scattering, and improved crystallinity. Higher spin speed
generally produces thinner and more homogeneous films, which facilitate
efficient carrier mobility and reduce trap-assisted recombination.
3.3 Application Suitability
The spin-coated Fe2O3 thin films
exhibit an optical band gap in the range of 1.84–1.90 eV with strong absorption
in the visible region, making them suitable for solar energy harvesting and
optoelectronic applications. The tuneable band gap and transparency at longer
wavelengths support their potential use as absorber or window layers in thin-film
solar cells and photoelectrochemical devices. The observed semiconducting
behaviour with nearly ohmic conduction confirms efficient charge transport
characteristics. The higher conductivity obtained at 3000 RPM suggests improved
crystallinity and reduced grain boundary scattering, enhancing carrier
mobility. These properties make the films promising candidates for photovoltaic
devices, photodetectors, gas sensors, electrochromic systems, and
photocatalytic applications.
4. Conclusion
Fe2O3
thin films were successfully deposited on glass substrates using the spin
coating technique at 2500 and 3000 RPM with a constant spin time of 60 s.
Optical studies revealed strong visible light absorption with a band gap
ranging from 1.84–1.90 eV, indicating suitability for solar and optoelectronic
applications. Electrical measurements confirmed semiconducting behaviour with
improved conductivity at higher spin speed due to enhanced film uniformity and
crystallinity. The study demonstrates that spin coating parameters
significantly influence the optical and electrical properties of Fe2O3
thin films. Therefore, controlled variation of deposition conditions provides
an effective route to tailor material properties for renewable energy devices
and electronic applications.
5. Acknowledgements.
One of the Authors Mr. Niranjan Samudre isdeeply
thankful to the Council of Scientific and Industrial Research (CSIR), New
Delhi, for providing financial assistance through the CSIR Fellowship, which
made this research possible. Authors are also greatly thankful to the Principal
of S.G. Patil ASC College Sakri for availing research facilities for this work.
6.
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