| dc.description.abstract |
The increasing interest in the interaction of light with electricity and
electronically active materials made the materials and techniques for producing
semitransparent electrically conducting films particularly attractive. Transparent
conductors have found major applications in a number of electronic and
optoelectronic devices including resistors, transparent heating elements,
antistatic and electromagnetic shield coatings, transparent electrode for solar
cells, antireflection coatings, heat reflecting mirrors in glass windows and many
other. Tin doped indium oxide (indium tin oxide or ITO) is one of the most
commonly used transparent conducting oxides. At present and likely well into
the future this material offers best available performance in terms of
conductivity and transmittivity combined with excellent environmental stability,
reproducibility and good surface morphology.
Although partial transparency, with a reduction in conductivity, can be obtained
for very thin metallic films, high transparency and simultaneously high
conductivity cannot be attained in intrinsic stoichiometric materials. The only
way this can be achieved is by creating electron degeneracy in a wide bandgap
(Eg > 3eV or more for visible radiation) material by controllably introducing
non-stoichiometry and/or appropriate dopants. These conditions can be
conveniently met for ITO as well as a number of other materials like Zinc oxide,
Cadmium oxide etc.
ITO shows interesting and technologically important combination of properties
viz high luminous transmittance, high IR reflectance, good electrical
conductivity, excellent substrate adherence and chemical inertness. ITO is a key
part of solar cells, window coatings, energy efficient buildings, and flat panel
displays. In solar cells, ITO can be the transparent, conducting top layer that lets
light into the cell to shine the junction and lets electricity flow out. Improving
the ITO layer can help improve the solar cell efficiency. A transparent
ii
conducting oxide is a material with high transparency in a derived part of the
spectrum and high electrical conductivity. Beyond these key properties of
transparent conducting oxides (TCOs), ITO has a number of other key
characteristics. The structure of ITO can be amorphous, crystalline, or mixed,
depending on the deposition temperature and atmosphere. The electro-optical
properties are a function of the crystallinity of the material. In general, ITO
deposited at room temperature is amorphous, and ITO deposited at higher
temperatures is crystalline. Depositing at high temperatures is more expensive
than at room temperature, and this method may not be compatible with the
underlying devices.
The main objective of this thesis work is to optimise the growth conditions of
Indium tin oxide thin films at low processing temperatures. The films are
prepared by radio frequency magnetron sputtering under various deposition
conditions. The films are also deposited on to flexible substrates by employing
bias sputtering technique. The films thus grown were characterised using
different tools. A powder x-ray diffractometer was used to analyse the
crystalline nature of the films. The energy dispersive x-ray analysis (EDX) and
scanning electron microscopy (SEM) were used for evaluating the composition
and morphology of the films. Optical properties were investigated using the UVVIS-
NIR spectrophotometer by recording the transmission/absorption spectra.
The electrical properties were studied using vander Pauw four probe technique.
The plasma generated during the sputtering of the ITO target was analysed using
Langmuir probe and optical emission spectral studies. |
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