Investigations on the structural, optical and electrical properties
of Nb-doped SnO
2
thin films
V. Gokulakrishnan
•
S. Parthiban
•
K. Jeganathan
•
K. Ramamurthi
Received: 26 October 2010 / Accepted: 23 March 2011 / Published online: 5 April 2011
Ó Springer Science+Business Media, LLC 2011
Abstract Niobium-doped tin oxide thin films were
deposited on glass substrates by the chemical spray pyro-
lysis method at a substrate temperature of 400 °C. Effects
of Nb doping on the structural, electrical and optical
properties have been investigated as a function of niobium
concentration (0–2 at.%) in the spray solution. X-ray
diffraction patterns showed that the films are polycrystal-
line in nature and the preferred growth direction of the
undoped film shifts to (200) for Nb-doped films. Atomic
force microscopy study shows that the surface morphol-
ogy of these films vary when doping concentration
varies. The negative sign of Hall coefficient confirmed the
n-type conductivity. Resistivity of *4.3 9 10
-3
X cm,
carrier concentration of *5 9 10
19
cm
-3
, mobility of
*25 cm
2
V
-1
s
-1
and an average optical transmittance of
*70% in the visible region (500–800 nm) were obtained
for the film doped with 0.5 at.% niobium.
Introduction
Transparent and conducting oxide (TCO) thin films have
attracted a great deal of attention because of their unique
nature of low resistivity and high transmittance in the visible
range of solar spectrum [1–9]. These oxide thin films are
extensively used for a variety of applications which include
architectural windows, flat panel displays [2], thin film
photovoltaics [3], smart windows [4] and polymer-based
electronics [5]. SnO
2
-based thin films have been widely
studied because they are stable towards atmospheric condi-
tions, chemically inert and mechanically hard and they can
resist high temperatures [10]. These properties of SnO
2
have
aroused great interest in the development of a short wave-
length semiconducting laser, which has potential applica-
tions in manufacturing the next generation compact disc read
heads [11]. In addition to their applications as optical win-
dows for the solar spectrum, SnO
2
thin films have been
employed successfully in touch sensitive switches, digital
displays, electro chromic displays and gas sensors [12–14].
Pure and doped-SnO
2
thin films of various dopants have
been prepared by various techniques, such as magnetron
sputtering [15], sol–gel method [16], chemical vapour
deposition (CVD) [17] and pulsed laser deposition [18].
Among these techniques, chemical spray pyrolysis method
has a simple and inexpensive experimental arrangement and
has the advantages like ease of adding dopands, reproduc-
ibility, high growth rate and mass production capability for
uniform large area coatings, which are desirable for
industrial and solar cell applications. Doping of various
metals with TCO films has been demonstrated to be a
simple and effective way to enhance the film characteristics
and hence efforts have been made in this direction aiming at
increasing the conductivity, transmission and stability of
various TCOs [19, 20]. Doping is also often used to change
the conductivity properties of oxide films. The niobium
(Nb) atom has a similar outer shell electron configuration to
tin, and has atomic number comparable to that of tin.
Therefore, it is theorized that the Nb easily takes the place
of the tin atoms in the tin oxide. To the best of the knowl-
edge, no reports on the preparation of Nb-doped SnO
2
thin
films by spray pyrolysis technique are available. Hence in
this study, transparent and conductive Nb-doped tin oxide
V. Gokulakrishnan Á S. Parthiban Á K. Ramamurthi (&)
Crystal Growth and Thin Films Laboratory, School of Physics,
Bharathidasan University, Tiruchirappalli 620 024, India
e-mail: krmurthin@yahoo.co.in
K. Jeganathan
Centre for Nanoscience and Nanotechnology, School of Physics,
Bharathidasan University, Tiruchirappalli 620 024, India
123
J Mater Sci (2011) 46:5553–5558
DOI 10.1007/s10853-011-5504-x