1. Presented by
K.
Kamalakkannan

2. OutlineOutline
 Introduction
 History
 Application
 Structure and Polytype
 Doping
 Sample notation and Cutting
 Conclusion

3. All the electronic equipments needs Semiconducting materials. At an
early stage Si & Ge was dominate. Later GaAs used.
Looking for alternate materials for High temp, High power & High
frequency applications is the current field of research interest. So that
we need to develop wide Bg materials.
For this case, SiC materials are very useful, because of its
exceptional properties, like Wide band gap, High saturation electron
drift velocity, etc.,

4. The History of SiC
SiC was first observed in 1824 by the Swedish scientist Jons Jacob
Berzelius, when attempt to synthesis of diamond.
Naturally occurring SiC has been discovered by Henri Moission in 1905
in a meteorite- called Moissanite.
First man made SiC- starts in 1891, by Edward G. Acheson, when he was
running an experiment on the synthesis of diamonds.
Heating a mixture of clay (Aluminium silicate) & Coke (Carbon) in an
iorn bowl- Acheson got blue crystal named Carborundum.

5. Continue…
Lely in 1955 introduced a crystal growth technique to produce high
quality bulk SiC. But the problem of producing large area defect free
single crystal is difficult- So, device fabrication is also difficult.
Modified Lely method was developed by Tairov & Tsvetkov using
seeded SiC.
Recent and most common method is Vapor- phase epitaxy (VPE)- used
for epitaxial growth of SiC- in a CVD reactor.

6. Why we use SiC?…
Silicon carbide is a wide band gap IV- IV semiconducting material and it
is an attractive material among researchers for more than a century due to
its hardness next to diamond.
SiC is widely used because of it’s,
1. Extreme hardness (mohs hardness is around 9.2)
2. Light wear resistance
3. High thermal conductivity (3.4 W/cm k)
4. Wide energy band gap (3.2 ev)
5. High electric field breakdown strength (2.22 X106
V/cm)
6. High saturated electron drift velocity (2.2 X107
cm/s)
Wide band gap (3.2 ev)- Enables SiC to operate at extremely high temp,
high voltage.

7. Cont .,
High breakdown electric field- Enables the fabrication of high
voltage and power devices such as power transistors & diodes.
High thermal conductivity- SiC can operate at extremely high
power levels.
High saturated electron drift velocity- Can operate at high
frequency ( RF and Microwave).

8. Cont.,
At an early stage, the more attention is given to the mechanical property
of SiC – Used as an abrasive- such as sand paper & cutting tools .
It is a very hard material because of Its shorter bond length 1.89 Ao
between Si and C results in high bond strength and hardness.
Wide band gap materials are superior to Si due to their physical, chemical
properties. For this it is more difficult to excite electrons from VB to CB.
This causes reduction in leakage of currents & an increase in thermal
stability in a device- high temp applications.

9. Efficiency of ZnO : Rajkumar et al (2011) - 0.142 %
Kanmani et al (2012) - 0.163 %
Prabhu (2014) - 0.366 %
Efficiency of ZnSe QDs : G.Sfyri et al (2014) - 0.59 % (Using
FTO/TiO2/CdS/ZnSe/P3HT)
Bang et al (2009) - 5.6 X 10-4
%
So, here an attempt will be made to synthesize ZnSe thin film on
glass substrate and studied for solar efficiency where other
interesting properties will be analyzed simultaneously.
Number of thin film deposition methods are available - Among
them, CBD provides a more promising option - large scale
controllability, and low cost method[2]
Properties of some wide bandgap semiconductors

10. Micro elect ronic
applicat ionSiC is the only wide Bg material having SiO2 as native oxide- SiO2 as a
dielectric is needed for gate material in MOSFET. This can formed by
simple wet dry oxidation of SiC.
Inertness & high temp. stability of SiC is used in furnaces and combustion
engines.
SiC is also used as a sensor to detect nitric oxide, hydrocarbons and
oxides.
SiC is used in high frequency operations- microwave applications. It is
also used as a substrate for material synthesis.

11. Crystal Structure
and poly typeSiC – a binary compound, having equal Si & C, where Si-C bonds are
nearly co-valent with ionic contribution of 12% (Si is +ve, C is –ve
charged).
Smallest building element of SiC is a tetrahedron of a Si(C) atom
surrounded by four C(Si) atom in sp3
bonds.
Distance between Si-Si or C-C atom is ~3.08 Ao
, Si-C atom is ~1.89 Ao
.
So the distance between Si-Si and Si-C ratio is 3:1.
Basic elements of
SiC crystals: Tetrahedrons
containing (a) one C and four Si
(b) one Si and four C atoms.

12. Cont.,
Most important property of SiC is polytypism- a 1D type polymorphism.
SiC structurally differ by the stacking sequence of a close packed Si-C bi-
planes along the c-axis.
More than 200 different polytypes of SiC are known to exist. Among
them- Cubic, Hexagonal, Rhombohedra polytypes of SiC are common.
Only one cubic(C) polytype referred as- β- SiC is the available poly type,
all other α- SiC (either a hexagonal (H) or rhombohedral(R)) symmetry.
The Si- atom lying exactly above the C- atom along the stacking axis (C-
axis). Each type characterized by the stacking sequence of layers A, B
and C.

13. Cont.,
Stacking the layers in ABC order will produce Zinc blend (Cubic)
structure and the staking sequence of AB is wurtzite structure
(Hexagonal).
The crystalline structure of SiC: (a) the
three possible hexagonal positions (A, B,
and C) for Si and C atoms

14. Cont.,
Commonly used nomenclature for describing the SiC polytypes is
Ramsdell notation, describing each polytype with a number followed by a
letter.
ex: 2H- SiC = Wurzite crystal structure.
3C- SiC = Zinc blend structure.
15R- SiC = Rhombohedral.
The number denotes the counts of the double layer in one period, the
letter stands for symmetry.
Most common available forms in SiC are: 3C- SiC, 2H- SiC, 4H- SiC,
6H- SiC and 15R- SiC.

15. Cont.,
3C SiC poly type 6H- SiC poly type

16. Cont.,
3C- SiC 2H- SiC
4H- SiC 6H- SiC

17. Cont.,
The stacking sequence of the common form of SiC are:
ex: 2H- SiC = AB.
3C- SiC = ABC.
4H- SiC = ABCB
6H- SiC = ABCACB
15R- SiC = ABCACBCABACABCB.
The path of covalent bonds between Si & C atoms on the projected
atomic positions onto a (11-20) plane is traced for determination of
polytype.
The turning points of Zig-Zag patterns in a Si-C pair is said to be
hexagonal(h), between the turning points is called cubic (k).

18. Cont.,
The stacking sequences of four common
SiC polytypes. The different cubic
and hexagonal lattice sites are marked.

19. Cont.,
It is also possible to derive the ‘Hexagonality, of a Si-C polytype, which
is the percentage of the hexagonal sites out of whole crystal..
Notations and hexagonality of SiC polytypes with the corresponding numbers of
inequivalent lattice sites.
As the hexagonality increases from 0 to 100% the indirect Bg of SiC varies
from 2.3 (3C) to 3.33 (2H) eV.

20. Doping of SiC
SiC is a semi-insulator, which can made n &/or p type by doping with
impurities. n-SiC can be achieved by Nitrogen or Phosphorus doping and
p-SiC is achieved by doping with Aluminum, Boron, or gallium.
Metal like conductivity has been achieved by heavy doping with Al &
Boron.
Superconductivity is also achieved in 3C-SiC:Al, 3C-SiC:B & 6H-SiC:B
at 1.5K. .

21. Doping of SiC
Comparison of SiC polytypes (Electrical parameters)
4H- SiC 6H- SiC 3C- SiC
Band gap
(eV)
3.2 3.0 2.3
Intrinsic carrier
concentration (cm-
3
)
10-7
10-5
10
Electron mobility at
ND = 1016
cm2
/V s
II- C, aixs= 800 II C- axis: 60 750
Hole mobility at ND
= 1016
cm2
/V s
115 90 40
Donor (Nitrogen)
dopant
45 85 45

22. Sample notation-
SiC
Carbon face up orientation
The primary flat is the {1010} plane with the flat face parallel to the <1120>
direction.

23. Primary and secondary flat locations, and marking orientation,
silicon face up for carbon face polished wafers
Silicon face up

24. Cuttinng of SiC

25. Conclusion
SiC – IV-IV semiconducting material and widely used among researchers
for its excellent properties of wide range application
Wide band gap, High saturation electron drift velocity, High electrical
field breakdown strength, High maximum current density, Extreme
hardness and High thermal conductivity are the interesting factors of SiC-
Used in High power devices.
SiC- more than 200 known crystal structure- polymorphism. Common
forms are 3C-SiC, 2H-SiC, 4H-SiC, 6H-SiC & 15R-SiC.
Electrical parameters shows 4H-SiC is better for device application.
SiC- hard material, Cutting of the sample is done with diamond tipped
cutter.

26. Thank you