1. TRANSPARENT ELECTRONICS
POOJA A
S3 EC
ROLL NO:47

2. INTRODUCTION Invisible electronics
Implemented using transparent conducting films
Inorganic films are composed of TCOs
Organic films are composed of carbon nanotube networks and graphene
Employs wide band gap semiconductors
Applications include transparent LCD,OLED and solar cell

3. TRANSPARENT CONDUCTING OXIDES(TCO)
Doped metal oxides
Examples are indium oxide,tin oxide,zinc oxide and cadmium oxide
They should have more than 80% transmittance in the visible region and conductivity higher than 1000 S/cm
Mobility is limited by ionized impurity scattering
Most commonly used TCO at present is tin doped indium oxide.
Binary compounds of metal oxides without any impurity doping have also been developed for use as TCOs.

4. COMBINING OPTICAL TRANSPARENCY WITH ELECTRICAL CONDUCTIVITY
TCOs possess two contradictory physical properties
-high optical transparency
-high electrical conductivity
For combining optical transparency with electrical conductivity there are two ways:
-degenerate doping
-Burstein-Moss shift
Degenerate doping provides high mobility of electrons due to their small effective mass and low optical absorption
Burstein-Moss shift helps in broadening the optical transparency window

5. BURSTEIN MOSS SHIFT

6. FACTORS CAUSING ADVERSE EFFECT
The large carrier concentrations required for good
conductivity can cause an increase of optical absorption
due to
-Inter-band transitions at short wavelengths
-Intra-band transitions at long wavelengths
Plasma oscillations affect optical properties by reflecting electromagnetic waves of frequency below that of plasmon
Ionized impurity scattering affects charge transport

7. ELECTRICAL AND OPTICAL PROPERTIES OF TCO
Strong interactions between metal ns and oxygen 2p orbitals give rise to band structure similar for all oxides
Valence band formed by oxygen 2p interactions
Conduction band formed by Ms-Op interactions
TCO thin films should have very low absorption coefficient
The optical properties,i.e,transmission,reflection and absorption are determined by refractive index,band gap and geometry

8. BAND STRUCTURE OF TCO HOST

9. CARRIER GENERATION There are two methods: Substitutional doping
Doping with group III,IV amd VII elements
Considering shrinkage of the lattice,optical band gap width,charge density distribution and electron velocity the trend is In>Y>Sc>Ga
Oxygen reduction
Removal of oxygen atom from a metal oxide
If the free energy of formation is high oxygen vacancies create F centres else they become free carriers
Result in higher carrier densities but limits mobility

10. CNTs
Transparent conductors are fragile and tend to breakdown due to fatigue and hence CNTs are used as an alternative
They have high elastic modulus,high tensile strength and high conductivity
CNTs have a transmittance of more than 90% in the IR range.Hence they can be used as heat dissipators in solar cells.

11. APPLICATIONS Transparent washer Transparent laptop Transparent mobile
Transparent solar panel
Transparent
mobile