Indium tin oxide (ITO) is a transparent conducting oxide used in applications such as touchscreens and solar cells. It is deposited as a thin film using methods like thermal evaporation or sputtering. ITO has high electrical conductivity and optical transparency due to its large band gap. It is studied using techniques like Kelvin probe force microscopy that measure electrical properties at the nanoscale. While ITO enables important technologies, its production requires significant energy and indium is a scarce resource.

1. GAUTAM BUDDHA
UNIVERSITY
Optical and Electronic Properties of ITO and FTO
Submitted by :
Preeti choudhary
(17/MAP/O16)

2. Indium Tin Oxide (ITO)
• Indium tin oxide (ITO) is a ternary
composition of indium, tin and oxygen in varying proportions.
• It’s composition with a formulation of
74% In,
18% O2, and
8% Sn
• It is transparent and colorless in thin layers.
• In bulk form it is yellowish to grey.
• In the infrared region of the spectrum it acts as a metal-like mirror.

3. Physical properties
Melting point
• 1800–2200 K
• 1526–1926 °C
• 2800–3500 °F
Density
• 7120–7160 kg/m3 at 293 K
Bandgap
• Pale yellow to greenish yellow (in powder form)
• depending on SnO2 concentration
Color
• 4eV

4. • ITO is a heavily doped n-type semiconductor with a large bandgap of
around 4 eV.
• Because of the band gap, it is mostly transparent in the visible part of the
spectrum
• it is opaque in ultraviolet (UV) region because of band-to-band
absorption (a UV photon can excite an electron from the valence band to
the conduction band).
• It is also opaque in the near infrared (NIR) and infrared (IR), because
of free carrier absorption (an infrared photon can excite an electron from
near the bottom of the conduction band to higher within the conduction
band).

5. ITO has attractive properties including
• high level of transmittance in the visible region as well as electrical
conductivity that is unique.
• This is mainly due to ITO's highly degenerate behavior as an n-type
semiconductor with a large band gap of around 3.5 to 4.3 eV.

6. Indium tin oxide is one of the most widely
used transparent conducting oxides because of
its two main properties
Electrical conductivity
(electrical properties)
the measure of a material's ability to allow
the transport of an electric charge. Its SI is
the siemens per meter, (A2s3m−3kg−1)
Optical transparency
(optical properties)
the physical property of allowing light
to pass through the material without
being scattered

7. optical properties of a material define how it interacts with light
Refraction
refraction index
Polarization
Reflection
reflectance
Absorption
Photoluminescence (fluorescence)
Transmittance
Diffraction
Dispersion
Dichroism
Scattering
Birefringence
Color
Photosensitivity
Optical properties

8. Electronic Properties
Electron states in solids
Electrons in solids are in localized or delocalized states, levels, or orbitals. The inner or
core states are localized, and are very similar to the states in free atoms. The outer or
valence electrons are delocalized in the sense that the can extend outside the region of just
one atom
Electron binding energies
The binding energy is the minimum energy needed to remove a
particular electron from the atom.

9. Band-gap states
The band-gap in semiconductors and insulators results from the interplay
between the electron wavelengths and the symmetric arrangement of atoms
in the solid. At the surface, the symmetry is broken which relaxes the
condition that inhibits electrons to propagate inside the lattice. The
symmetry is also broken by defects and impurities. Broken symmetry
results in electronic states which can exist in the band gap. The existence of
states in the band have that pertain to the surface, or surface states
Photoelectric threshold
This is the minimum energy needed to extract an electron from the solid.

10. Photoelectric threshold
This is the minimum energy needed to extract an electron from the
solid.
Work Function
The energy difference between the Fermi level and the vacuum level. For a metal,
this is the minimum energy required to eject an electron into vacuum (at T = 0 K),
since the electrons with the minimum binding energy are at the Fermi level. At T >
0 K it is found that the work function varies slightly with temperature. Also, and
independently from the previous statement, the minimum energy to emit an
electron from the solid depends on the sensitivity of the measurement, since the tail
of the Fermi-Dirac distribution extends beyond the vacuum level. For most
metals, f is about 4-5 eV, the minimum values are around 1.5 eV for metal surfaces
with an adsorbed layer of cesium.
In a semiconductor and insulator, the work function is defined in the same way
as in the metal: f = Evacuum - EFermi, but now there are no electrons at the Fermi
level.

11. optical and electrical properties of thin
films are studied by
X-ray diffractometry
Raman spectroscopy
Scanning electron
microcopy
UV–visible spectrometry
Atomic force microscopy
showed the formation of
the cubical phase of polycrystalline thin films
morphological analysis
showed the formation of ginger like structures
Hall measurements confirmed n-type conductivity of films with low
electrical resistivity (ƪ) 10^3 Ω cm and high carrier concentration
(n) 10^20 /cm3
interactions between a specific atom and its
neighboring atoms,
used in quantitative chemical analysis
used to observe vibrational, rotational, and other low-
frequency modes in a system.

12. fluorine doped tin oxide (FTO)
• The work function of FTO is commonly cited as 4.4 ev.
• Electrically conductive for heated and thermal control, electrostatic
dissipation and reduced transmittance of electromagnetic radiation.
• Color neutral glass inhibits reflector color, increases light transmittance
and minimizes haze to optimize clear visibility.
• Easily fabricated durable pyrolytic surface can be handled, cut, insulated,
laminated, heat-strengthened and tempered using standard techniques.
• Durable Pyrolytic Surface provides unlimited shelf life, minimizes rubs
and scratches, and will not oxidize or change color over time.
• Available in a variety of glass thicknesses and surface resistivities ranging
from 7 Ω/sq. up to 13 Ω/sq.

13. METHODS OF DEPOSITION
• Thin films of indium tin oxide are most commonly deposited on surfaces
by
thermal evaporation technique.
• Often used is electron beam evaporation,
sputter deposition techniques.

14. • A form of Thin Film Deposition (a vacuum technology for applying coatings of
pure materials to the surface).
• Films in the thickness range = angstroms to microns and can be a single material, or
can be multiple materials.
• The materials to be applied with Thermal Evaporation techniques can be pure
atomic elements including both metals and non metals, or can be molecules such
as oxides and nitrides.
• The object to be coated is referred to as the substrate, and can be any of a wide
variety of things such as:
semiconductor wafers,
solar cells,
optical components, or many other possibilities.
Thermal evaporation technique

15. Physical Vapor Deposition (PVD) / Thermal
Evaporation
Diagram of Thermal Evaporation Process

16. Thermal Evaporation
Method
Heating a solid
material
vapor then rises above
this bottom source
surfaces intended to
be coated
Filament Evaporation
Heat element
Means of
Heating
Thermal Evaporation Method

17. Benefits of ITO
• a transparent conductor for LCDs is that ITO can be precisely etched into fine
patterns It is so sensitive to acid that it tends to get over-etched by an acid
treatment.
• ITO is not affected by moisture and it can survive in a copper indium gallium
selenide solar cell for 25–30 years on a rooftop.
• Used in nanotechnology to provide a path to a new generation of solar cells
Solar cells made with these devices have
the potential to provide low-cost,
ultra-light weight, and
Because of the nanoscale dimensions to absorb light within a specific narrow band
of colors.

18. Constraints and trade-offs
• The main concern about ITO is the cost
(the cost per cell is quite small too)
• Indium tin oxide is harmful in that it may cause mild irritation.
• ITO is typically deposited through expensive and energy-intensive
processes that deal with physical vapor deposition (PVD).

19. Kelvin probe force microscopy
•Kelvin probe force microscopy was proposed by Nonnenmacher in 1991 as a tool
to measure the local contact potential difference between a conducting atomic force
microscopy (AFM) tip and the sample.
• KPFM has been used extensively as a unique method to characterize the Nano-
scale electronic/electrical properties of metal/semiconductor surfaces and
semiconductor devices.
•Recently, KPFM has also been used to study the electrical properties of organic
materials/devices and biological materials

20. Kelvin probe force microscopy

21. Working Principle
• We applied an ac modulation bias
VAC (frequency fAC) with a dc
offset bias DC voltage between a
tip and a sample to generate an
electrostatic force between the tip
and the sample as shown in Fig
point (1).
• The cantilever deflection by an
electrostatic force is detected by a
photo detector and then the
component signal of frequency
fAC is derived by a lock-in
amplifier point (2).
• • The signal is transferred to a
feedback controller as shown in
Fig point (3)

22. • The intended potential,
that is, CPD is obtained
by adjusting the dc offset
bias VDC so that the
component signal of
frequency fAC becomes
zero.