19-09-2012, 01:47 PM
High mobility Ti-doped In2O3 transparent conductive thin films
High mobility Ti-doped In2O3.pdf (Size: 488.25 KB / Downloads: 39)
Abstract
Highly conducting and transparent titanium (Ti)-doped indium oxide (In2O3) films were deposited on sapphire substrate by ablating the
sintered In2O3 target containing 1–10 wt.% TiO2 with a KrF excimer laser (λ=248 nm and pulsed duration of 20 ns). The effect of growth
temperature from room temperature to 600 °C and oxygen pressure (1.0×10−4–2.5×10−7 bar) has been studied by analyzing structural, optical,
and electrical properties of these films. The conductivity, carrier concentration and mobility of the films grown at 600 °C are 10,858 S cm−1,
4.3×1020 cm−3 and 159 cm2 V−1 s−1 respectively. This is the highest mobility ever obtained in doped In2O3 films.
Introduction
Unique transparent and conducting properties of transparent
conducting oxides (TCO) lead them for numerous optoelectronic
applications [1]. Among these tin doped indium oxides
have received much attention due to its low electrical resistivity
and high transparency, although the mobility of these films is
not very high (29 cm2 V−1 s−1) [2]. There is an increasing
interest in TCO with high mobility to increase electrical
conductivity without sacrificing optical transparency [3].
According to the Drude model, optical transparency depends
on the plasma frequency, [ωp=(ne2 / ɛ0m⁎)1/2, where, n is the
charge carrier concentration, e is the charge, ɛ0 is the free space
permittivity, and m⁎ is the effective free electron mass], which
shifts to shorter wavelengths with increasing carrier concentration
[4]. Therefore, one has to increase the mobility not carrier
concentration, to obtain the films having high conductivity as
well as wide transparency window.
Results and discussion
Fig. 1 shows the X-ray diffraction patterns of Ti-doped In2O3 (TIO)
films which deposited at substrate temperatures of 30, 200, 400 and
600 °C. It is observed that the films are randomly oriented on the sapphire
substrate. No additional peaks due to the addition of titanium in indium
oxide films were observed and this indicates the absence of an impurity
phase in the films. That is, the diffractograms provide support for single
phase crystalline indiumoxide (body centered cubic lattice) [6]. The films
were amorphous up to 300 °C, above which polycrystalline cubic
bixbyite In2O3 phase appears. Using Scherrer equation [7] the average
particle size in the films grown at 400 °C and 600 °C was calculated to be
7.1 nm and 8.6 nm, respectively. The percentage strain in the particles is
obtained to be 3.5% for both the films.
Conclusions
We have fabricated highly conducting and transparent
titanium-doped indium oxide films by pulsed laser deposition
technique. The mobility of the film grown is 159 cm2/V s. This is
more than three times the value of commercially available TCO,
which suggests that these films have significant commercial
relevance.