Materials Sciences and Application, 2011, 2, 1022-1026
doi:10.4236/msa.2011.28138 Published Online August 2011 (
Copyright © 2011 SciRes. MSA
Investigation of Polyaniline Thin Film and
Schottky Junction with Aluminium for Electrical
and Optical Characterization
Pronob Jyoti Saikia, Pratap Chandra Sarmah*
Department of Electronics, North-East Institute of Science and Technology, Jorhat, India.
Email:, *
Received April 1st, 2011; revised May 6th, 2011; accepted May 23rd, 2011
Polyaniline Powdered sample was chemically synthesized using aniline and doped with HCl. Ultra thin film and Schot-
tky junction with Al metal have been fabricated from this powdered sample Ultrathin film of polyaniline shows amor-
phous nature of the film. Two activation energies of these films at two different temperatures regions within 25 - 120 ˚C
have been observed. Schottky Junction with Al metal shows that the diode ideality factor is much higher than unity.
Barrier height of this Schottky junction is estimated to be around 0.61 eV. C-V plot of the junction indicates that the
carrier concentration is about 1015 cm–3. There are various factors found to affect the junction to deviate from ideal
Schottky behaviour.
Keywords: Aniline, Activation Energy, Diode Ideality Factor, Barrier Height
1. Introduction
Among all conducting polymers, po lyaniline (PANI) and
its derivatives have attracted much interest worldwide.
Because of chemical stability, simple polymerization,
high conductivity, polyaniline has been used in various
application, like, optoelectronics, bio-sensors, gas sen-
sors, microelectronics etc. [1-5]. Several methods of pre-
paration of PANI film such as, spin coating, drop coating,
electrochemical deposition, thermal evaporation, emul-
sion polymerization, Langmuir-Blodgett (L-B) technique
etc. [6-11] have been reported by various workers. Poly-
aniline may be doped by protonic acid and oxidative
doping [12]. It has been reported that the conductivity of
film cast from solution of polyaniline camphor sulpho-
nate in m-cresol is of about 2 order of magnitude higher
than that of polyaniline protonated with mineral acid and
organic acid [13]. Different inorganic and organic acids
of different concentration have been used in the synthesis
of PANI and this protonated products of polyaniline dif-
fers in stability and conductivity [14]. The effect on
property and growth of polyaniline produced by ionic
sputtering in presence of electric and magnetic field was
studied by P. Stakhria et al. [15]. Nanocomposite of PA-
NI is an important candidate for device application in
biosensor, gas sensors, optoelectronics etc. [16-19].
Schottky junction of polyaniline with metal is another
important subject and have great technological impor-
tance [20]. This is recently gaining momentum for device
application. Electrical and optical properties of polyani-
line and its composite is however dependent on prepara-
tion techniques and matrix material used [21]. The aim of
this study is to see the various properties of the ultra thin
film and Schottky junction of HCl doped PANI and to
improve the quality for device fabrication. In the process,
we have prepared powered polyaniline by chemical syn-
thesis method and produced ultra thin films by simple
technique. Electrical and optical properties of these films
and Schottky junctions with Al metal have been investi-
2. Experimental
2.1. Preparation of Polyaniline Powder
Chemical Synthesis of polyaniline in the form of emar-
aldine salt was done by the general procedure using re-
dox polymerization of aniline in presence of an oxidant,
ammonium peroxidisulphate (APS) and using HCl as
dopant. Freshly distilled aniline (4 ml) in 50 ml of 1M
HCl solution at 2 to 3˚C was stirred for 20 minutes and
subsequently added 1M APS solution (25 ml) drop wise
at a rate of 5 drops/minutes. The process continued till
Investigation of Polyaniline Thin Film and Schottky Junction with Aluminium for Electrical and Optical Characterization1023
the whole quantity was added and the solution turned
green. Stirring of the compound continued for about 3
hours after which the solution was kept for overnight.
The precipitate was treated with Tetrahydroforen to
eliminate other oligomers and was filtered using funnel.
The product was dried in an oven for 24 hours at 45˚C to
get the powder.
2.2. Preparation of the Film and Junction
The powdered sample of PANI was dissolved in Di-
methyl Sulfoxide (DMSO) in a beaker with continuous
stirring for about 4 hours. The solution was filtered and
drops of it were placed over a glass slide already cleaned
by chemical wash and subsequently in ultrasonic bath.
The drops were spread over by small glass spoon to
make in the form of film. For fabrication of junction,
ITO coated glass substrate were used after proper clean-
ing. This was dried in a specially made vacuum chamber
which was fitted with a heater and a temperature con-
troller. The temperature was maintained at 45˚C for dry-
ing in vacuum for about 5 hours. Four sets of ultrathin
films in the ranges from 200 Å to 400 Å were produced
in a cycle to study various parameters. One set of film so
produced was taken to the thermal evaporation unit for
deposition of electrodes. Gap type sample was made by
using two co-planer electrodes separated by a gap to
study electrical properties. Two electrodes of pure silver
were deposited onto the film keeping a gap of 1 mm us-
ing a mask. For fabrication of junction, high purity Al
foil (99.99% purity) was vacu um deposited onto the film
that was already prepared over the ITO coated glass slide
in the form of small disc shaped electrodes. The sche-
matic diagrams of gap type and sandwich type structure
are shown in Figure 1.
2.3. Experimental Arrangement
The samples of polyaniline film and junction so prepared
were kept in a departmentally designed vacuum chamber
for studying different characteristics. It is a glass cylin-
drical chamber of 35 cm length and 14 cm in diameter. It
is fitted with some electrical feedthroughs for electrical
and temperature controlling arrangement and a has gas
inlet valve. The chamber could be evacuated by a rotary
pump. All measurements were carried out in this cham-
ber keeping the sample in vacuum.
The structural investigatio n of the powered Polyan ilin e
and film so prepared was done by XRD spectrometer
(JDX-IIP3A). Absorption spectra was taken by a UV-Vis
spectrometer (Specord-200). IR absorption was recorded
by a fourier Transform spectrometer (Perkin Elmer Sys-
tem 2000). Electrical characteristics were measured by a
electrometer amplifier using two probe method. The
temperature effect was measured in the chamber as men-
tioned above at a vacuum of 10–4 torr.
3. Results and Discussions
3.1. For the Films
XRD spectra of the powdered and thin film samples
show nearly amorphous nature of the samples (Curve A
of Figure 2). However, with increase of thickness, the
film grows in grains and at higher thickness, the films
tends to be polycrystalline in nature. The PANI peak at
around 2θ = 9.5˚ has been indicted in the curve B of Fig-
ure 2. Similar observation has also been reported by other
workers [22] in PANI film. Figure 3 shows the FT-IR
spectra of PANI film. As is seen from the figure, the
peaks around 1563 cm–1 and 1476 cm–1 correspond to the
absorption upon quinoid ring and is closed to that corre-
sponding to the absorption of benzene ring (1502 cm–1).
The peak around 1470 cm–1 can be attributed to torsion
C-N oscillation in Alkyl chain and peak at 1301 cm–1to
torsion oscillation C-N in the Benzene ring. The peak at
1119 cm–1 can be attributed to in plane v alance oscilla tion
C-H. UV-Vis spectra (Figure 4) indicates the absorption
peaks at 3.8 eV and 4.1 eV of doped polyanilene and
these can be attributed to the transition from lower pola-
ron to upper polaron and to the conduction band respec-
tively [23].
A plot of conductivity σ versus 103/T for the film in
the range of 25˚C to 120˚C (Figure 5) of a typical sam-
ple shows that conductivity increases with temperature
within this range.
The conductivity may be express as :
Figure 1. Sample for measurement.
Copyright © 2011 SciRes. MSA
Investigation of Polyaniline Thin Film and Schottky Junction with Aluminium for Electrical and Optical Characterization
Figure 2. XRD spectra of HCl doped PANI film. (A) Thin
film of PANI (B) Thick film of PANI.
Figure 3. FTIR spectra of a typical doped film of PANI.
Figure 4. UV-Vis spectra of the doped film of PANI.
σ = σ0 Exp (–Ea/kT) (1)
where, σ0 is pre exponential factor, k, T and E
a are the
Boltzmann constant, absolute temperature and activation
energy respectively. The conductivity may be attributed
to hopping conduction model where two types of con-
ductivity components are combined such that σ can be
written as:
Figure 5. The Temperature versus Conductivity pl
ot of typical doped PANI film.
σ = σ1 + σ2 (2)
where, σ1 and σ2 are inter chain and intra chain respec-
tively. Activation energy estimated in the lower tem-
perature range is about 0.5 eV and at higher temperature
is about 3.5 eV. Similar observations in polyaniline film
have been reported by previous workers [24-25]. Yakup-
hanoglu et al. [26] have reported three regions for tem-
perature variation of resistivity in polyaniline film.
3.2. For the Junction
Al/PANI/ITO junction was fabricated as mentioned
above for studying various parameters. The junction
produced by Al on doped PANI film shows rectifying
nature of the junction (Figure 6). ITO with high work
function make ohmic contact to PANI (p-type). The
current density J and voltage V can be expressed by the
Richardson’s equation as,
J = Jo Exp (qV/kT) (3)
where Jo is the saturation current density and can be
written as :
Figure 6. Current density versus Voltage characteristics of
the Al/PANI/ITO structure.
Copyright © 2011 SciRes. MSA
Investigation of Polyaniline Thin Film and Schottky Junction with Aluminium for Electrical and Optical Characterization1025
Jo = A* T2 Exp (–Øb/kT) (4)
where A* and Øb are the Richardson constant and effec-
tive barrier height respectively. The saturation current
density is estimated to be around 5.4 × 10–3 A/sq·cm.
C2-V plot under reverse bias condition at 10KHz has
been shown in Figure 7. The plot of the junction shows
almost a linear relationship indicating the average uni-
form charge distribution in the space charge region. The
carrier concentration estimated from the slope is found to
be around 1015 cm–3. The diffusion potential V0 obtained
from the graph is around 0.58 eV. Barrier height esti-
mated from the saturation current density Jo using A*
value as 120 AK–2·cm–2 is found to be 0.61 eV. This val-
ue is however almost agree with the value of 0.6 eV de-
rived from the diffusion potential after necessary correc-
tion. Wei-chih chen et al. have also reported similar bar-
rier height for Al/PANI junction [27]. The barrier height
above 1.5 eV for boron trifloride doped PANI with Al
metal has been also reported [28].
The diode ideality factor n of these junctions are high-
er than unity. An estimate of diode ideality factor shows
to be around 8. The various factors responsible for diode
ideality factor greater than unity are, presence of an in-
terfacial layer, recombination of charges, migration of
electrode materials etc. One possible cause is the pres-
ence of the aggregation of primary and secondary parti-
cles arising during polymerization giving rise to two dif-
ferent transport mechanisms [29]. Recombination in the
depletion region is another possible cause. This also con-
tributes to the fact that reverse current is not showing
saturation. Presence of a very thin interfacial layer is not
ruled out. This is formed while transferring the film to a
vacuum evaporation chamber for depositing the counter
electrode. Similar affect of interfacial layer and effect on
diode ideality factor have been repo rted by earlier work er
in metal/polymer junction [30]. Since the car-
rier concentration is moderate, the current transport is
Figure 7. Voltage versus Capacitance plot of the junction of
figure 6.
mainly dominated by the thermionic emission process.
Similar observations on Al/PANI junction have also re-
ported by previous workers [31].
4. Conclusions
Thin film of HCl doped PANI and Schottky junction
with Al have been fabricated. Ultra thin film of PANI
produced in this process is amorphous in nature. The
UV-Vis spectra indicate the two transitions peaks. The
film shows two activation energies at 0.5 eV and 3.5 eV
at two temperatures regions respectively. PANI film
makes Schottky junction with Al and has high ideality
factor. The barrier height obtained for the junction is
around 0.6 eV. The current transport is believed to be
mainly dominated by thermionics emission process.
5. Acknowledgements
The authors wish to thank the Director, NEIST, Jorhat
for providing necessary facilities to carry out this work.
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