Sic an advanced semicondctor material for power devices

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Special Issue: 03 | May-2014 | NCRIET-2014, Available @ http://www.ijret.org 248
SIC: AN ADVANCED SEMICONDCTOR MATERIAL FOR POWER
DEVICES
Ajay Kumar1
, M S Aspalli2
1
Dept .Of Electrical & Electronics Engineering, PDA College of Engineering, Gulbarga – 585 102, Karnataka
2
Dept .Of Electrical & Electronics Engineering, PDA College of Engineering, Gulbarga – 585 102, Karnataka
Abstract
Silicon carbide (SiC) is a wide band gap material that shows great promise in high-power and high temperature electronics
applications because of its high thermalconductivity and high breakdown electrical field. This paper describes how the outstanding
physical andelectronic properties ofSiC permit the fabrication of devices that can operate athigher temperature and power levels than
devices fabricated from other material such as silicon orGaAs. In spite of, recent electronics depends primarily upon Silicon based
devices;this material is not capable of handling many greater requirements. Devices which operate at high frequency, at high power
levels and are to be used in seriousenvironments at high temperatures and high radiation levels required other materialswith wider
band gaps than that of silicon. Many space and ground based application rather than satellite applications also have a requirement
for wide band gap materials. SiC also has great strength for high power and frequency operation due to a high saturated drift
velocity. The Wide band gap permit for unusual optoelectronic applications that include blue light emitting diodes and ultraviolet
photo detectors New areas involving gas sensing and RF applications offer significant promise. Overall, the properties of SiC make it
one of the best prospects for extending the capabilities and operational regimes of the current semiconductor device technology.
Keywords: Silicon carbide, wide band gap semiconductor utility system, power electronics device, physical properties.
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1 INTRODUCTION
Silicon carbide (SiC) is the perfect material between silicon and
diamond. The crystal lattice of SiC is exactly similar to silicon
and diamond, but exactly half the lattice sites are filled by
silicon atoms and remaining half the lattice sites by carbon
atoms. Like-diamond SiC has electronic properties better
properties to silicon.
The wide band gap makes the device operate at high electric
fields, and the reduction in intrinsic carrier concentration with
increase in band gap enables the device to operate at high
temperatures. SiC is a wide band gap (3.2eV) Semiconductor
with high thermal conductivity, high breakdown electric field
strength, high-saturated drift velocity, and high thermal
stability. Therefore, silicon carbide is extremely durable and
useful for many high power, high frequency, and high
temperature applications. The thermal leakage current in SiC is
sixteen orders-of degree lower as well as temperature rises, the
escape(leakage) current increases, but the temperature where
the leakage current would disturb the circuit operation is over
1000 °C in SiC, compared to about 250 °C in silicon. The SiC
electronic period began in the early 1990's whenSiC based
single-crystal wafers became commercially available for the
first time. During the between years, many different electronic
Devices have been demonstrated in SiC with performance
frequently exceeding the theoretical restriction of silicon. These
include Pn diodes, MOS field-effect transistors
(MOSFETs),metal-Semiconductor field-effect
transistors(MESFETs), and bipolar transistors (BJTs.).
2 CRYSTAL STRUCTURE AND POLYTYPISM
The SiC‟s crystalline structure and its polytypic nature
influence of polytypism on the physical properties of SiC.
Silicon carbide is a binary compound containing equal amount
of „Si‟ and „C‟, whereSi-C bonds are nearly covalent with an
ionic contribution of 12% (Si positively, „C‟ negatively
charged). The smallest building element of any SiC lattice is a
tetrahedron of a Si (C) atom surrounded by four C (Si) atoms in
strong sp3-bonds. Therefore, the first neighbour shell
configuration is identical for all atoms in any crystalline
structure of SiC. The basic elements of SiC crystals are shown
in Figure1.
Fig. 1 Basic elements of SiC crystals: Tetrahedrons containing
(a) one C and four Si (b) one Si and four C atoms. [1]

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3 PROPERTIES OF WIDE BAND GAP SEMI-
CONDUCTORS
Table 1 compares the physical properties of SiC to other
importance semiconductor materials such silicon and GaN. The
wideband gap material with the most attractive characteristics is
diamond. However, a growth process ability of producing mono
crystalline diamond in required quantities suitable for
semiconductor substrates is not sufficiently available. It is
necessary to note that the physical properties stated for SiC
extend into the temperature regime much in excess of 300°C
which is the almost upper limit of the operational set of
conditions for silicon based devices.
Wide band gap materials are less influenced to thermal
difficulties and usually have high breakdown electric fields
which permit for increased isolation between devices and
higher packing densities. Higher thermal conductivities are also
of advantage in extent the on-off time (duty cycle) and
maximum device packing density. Maximum frequencies/speed
at which the devices operated mainly depends on the saturated
drift velocity which is clearly an advantage for SiC. In addition,
the less dielectric constant for SiC raises its value for high
frequency device operations. Further discussion and
comparison among the different semiconductor materials and
their properties are in given in Table-1.
Table 1 Comparison of Semiconductor Characteristics [3, 4, 7]
It is important to mention that the electron mobility and the
breakdown electric field are depending on the doping level. The
table shows the properties for some standard values.
The SiC substrates can be made in different polytypes i.e. 3C-
SiC, 4H-SiC and 6H-SiC.The ones which are mainly used are
4H-SiC and 6H-SiC. 4H-SiC is best for electronic applications
due to its higher carrier mobility and wider band gap in the
comparison of other poly types.
Fig. 2GaN Vs SiC Vs Si of their electrical properties [5]
The intrinsic carrier concentration of SiC as a function of
energy band gap (Eg) is expressed in equation 1.
From equation (1) one can see that the intrinsic carrier density
is exponentially decreasing with increasing band gap. This
means that SiC will have a much lower intrinsic carrier density
than Si at a given temperature. The breakdown voltage of a 4H
SiC junction decreases only by 8% when the temperature
changes from room temperature to 623 °C. It follows from
equation (1) that the diffusion current in a Pn-junction is
varying with the square of the intrinsic carrier density. Hence,
Silicon Carbide Pn-junction has many orders of magnitude
lower leakage current than a corresponding Silicon junction at
elevated temperatures.
The main contribution to on-state losses in a unipolar device is
due to the on-state resistance of the drift region. Thus a good
way to compare SiC and Si is to compare the specific
Resistance R.
Assuming an abrupt, one-dimensional, non punch trough
junction fabricated in a uniformly doped semi conductor layer
the specific on-resistance is expressed as [3, 4]
In the above equation VB is the breakdown voltage (V), µn is
the electron mobility (cm/V·s), �is the permittivity (C/V-cm)
and E stands for the critical electric field (V/cm). When two
devices are compared it is reasonable to choose devices with the

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same breakdown voltage from Equation(2) it is seen that the
resistance decrease with increasing electron mobility and
critical electrical field. This equation can give an approximation
of the ratio between the theoretical resistance in Si and SiC.
Silicon Carbide has one orderof magnitude higher value of the
critical field than Silicon, thus the on-state resistance will be
much smaller in SiC. To perform a more accurate calculation it
is necessary toconsider the mobility‟s and the breakdown
electric fields dependency on the doping level N.
The aim of the critical electric field with a semiconductor
device is that they can either block a voltage, or conduct a
current with low power loss. As seen in Fig. that the W is
depletion region width at the electric field distribution at inner
side of the device.
Fig 3Electric field distribution at inner side of the device at
Depletion region width [4]
4 APPLICATIONS OF SIC
4.1 Sic – A Widely Used Material
The material qualities of SiC have great potential, before the
emergence of microelectronics applications based on SiC, to
unique mechanical properties, so SiC is used as an abrasive in
sand, in polishing agents or in cutting tools.
SiC is one of the hardest materials known to man, only
diamond and boron nitride are harder. The short bond length of
1.89 Å between „Si‟ and „C‟ atoms result is in high bond
strength and excellent hardness. However, this makes SiC
wafers difficult to cut and polish. The strong bonds do also
create a large band gap that gives SiC‟s high refractive index
accompanied by a wide transparency over the visible spectrum,
optical intelligence, and resistance to chemical and harsh attack.
Recently high purity, almost colourless Moissanite crystals
become available, leading to the development of SiC gemstone
that have a beneficial influence on SiC semiconductor. Due to
relatively low density, SiC can be used even in space
applications, e.g. for ultra-lightweight mirrors. It is also
appropriate for bearings with the hardness and toughness.
4.2 Wide Band Gap Semiconductors
The wide area applications of SiC, is the most promising area is
semiconductor processing. The wide band gap materials are
better to silicon due to their physical and electrical properties.
The properties of different wide band gap semiconductors,
selected from the position giving a better view of
microelectronics applications. For e.g. in SiC the probability of
thermal excitation of an electron over the band gap is 10^-26 at
room temperature, i.e. there are no thermally excited electrons
in the conduction band. The wide band gap is also accompanied
by considerably higher breakdown voltage as compared to
silicon. This means that for power devices with similar
blocking voltage capabilities, the one made of silicon must have
about 100 times lower doping level in a 10 times thicker layer,
as compared to a SiC device.
4.3 SiC for Microelectronics Applications
The wide band gap semiconductor having silicon dioxide
(SiO2) as native oxide, similarly to silicon is studied in SiC.
SiO2 as a dielectric is needed for surface passivation of SiC
devices, as well as for a gate material in metal oxide-
semiconductor field-effect transistors (MOSFETs) and related
structures. Silicon dioxide can be formed by simple wet or dry
oxidation of SiC.
4.4 High Voltage Devices
SiC high voltage devices can be realized on much thinner drift
layers then for Si and GaAs diodes, succeed high breakdown
voltage as well as lower on-resistance and good outcomes have
been demonstrated with a fixed improvement in performance.

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SiC junction Schottky barrier diodes (JBS) are interesting in the
600 – 3200V blocking voltage regime.
4.5 RF Power Devices
SiC devices have shown a very significant improvement and
better RF power performance to those available in Si or GaAs
devices. The RF power available from an impact ionization
avalanche transit time (IMPATT) diode in SiC is ~98 times
higher than in Si. The high temperature and high power SiC
electronic devices would make possible revolutionary
improvements to aerospace systems, even without cooling
systems. Substitution of hydraulic controls and additional
power units with spread over smart electro-mechanicals
controls ability of Harsh-surrounding environment (on all sides)
operation enables substantial jet-aircraft weight savings, and
reduced maintenance.
4.6 Optoelectronics
The wide band gap of the different SiC crystal structures such
as 4H-SiC, 6H-SIC make them Suitable for far Ultra Violet
radiation detection.
High temperature photo detectors are also under development,
Ultraviolet photo detectors that are constructed using the
different SiC Crystal structure/poly types in the form of 6H-SiC
and 4H-SiC have been used to recognise UV radiation in the
range 200-400 nm. On the other hand Ultraviolet enhanced
silicon based photodiodes, by contrast, does not have ability to
recognise below 300 nm. The detection peak for a-SiC
photodiodes is between 200-300nm, Doping of both U-and
&SiC can potentially be used to shift the detection peak. SiC
operates well up to 600°C- 800°C, while UV detection at these
high temperatures is not possible with Silicon Photodiodes
because of the low temperature handling capacity of silicon.
Dark current (“noise”) for SiC detectors is low; <10-9 A/cn~2
at 10V and 26°C, and 10-8 A/cn~2 at 10V and 350°C
compared to silicon at 10-7 A/cn~2 at 10V and 26°C. Silicon
Carbide is also an indirect band gap material which implies that
no SiC lasers are envisioned. Direct band gap material can
easily be achieved, however, from solid solutions ofSiC and
two other important materials with wide Gap, AIN and GaN
The wide gap range for these materials is about 4 to 6 ev with
lower values are achieved by using suitable acceptor and donor
impurities. Although SiC cannot be used as a lasing material, it
is a potential waveguide substrate for nitride based
optoelectronics. GaN is a potential wide band gap material for a
UV semiconductor laser. The nitride family, however, has
proven to be very difficult to grown in a single crystal form.
SiC has been successfully utilized as a substrate for growth of
many desirable nitrides with potential usefulness for UV
optoelectronics. Relatively high intensity 500 ~m blue LEDs
are now commercially available that have been fabricated from
GaN grown on the basal plane of one of the crystal structure
6H-SiC. In addition, composite structures composed of a GaN
hetero structure grown on an AIN waveguide which in turn has
been grown on a supporting substrate of SiC are expected to
provide a variety of promising optoelectronic devices.
4.7 Sensors
Semiconductor materials such as Silicon have already shows
their great useful properties for pressure sensors such as their
large piezoelectric coefficients. The current available
operational range of semiconductor pressure sensors is limited
up to about 490°C. There is however a growing demands for
sensors capable of operating at temperatures much greater than
490°C such as for automotive and avionic down- hole
exploration applications. SiC shows their great promising
electrical properties as semiconductor material for such
potential applications at high temperatures. A pressure sensor
that takes advantage of SiC‟s thermal indifference and hardness
could operate in extreme temperature and pressure conditions,
such as inside an engine or turbine under the earth.
5 CONCLUSIONS
In future with effective effort, wide band gap semiconductors
have the favourable time to appropriate the much needed utility
requirements to be incorporated power supply where the high
temperature, high drift velocity is needed. Among all the wide
band gap semiconductor materials diamond has the best
electrical properties; research on applying it for high power and
high temperature application is only in its preliminary stages,
because the processing problem is more unfriendly to solve
than any of the other material; however, it likely will be a very
significant material for power devices in 20-40 years. In the
transition period, there needs to be transition materials with
some superior properties. GaN and SiC power devices show
similarly advantages over Si (Silicon) power devices. GaN‟s
intrinsic properties are slightly better intrinsic properties than
SiC; however, there is no availability of pure GaN wafers, and
thus GaN needs to be grown over SiC wafer.
SiC Power devices technology is to a greater extent than GaN
technology and is most important in research and
commercialization efforts. The small improvement GaN
provides great power not be sufficient to change gears and use
GaN instead of SiC.SiC is the best transition material for future
power devices where high temperature and high power is much
needed.
REFERENCES
[1]. T.Paul. Chow, “SiCand GaN High- Voltage Power
Switching Devices”, Materials Science Forum, vol. 338 -342,
Pp 1155-11 60, 2000
[2].Baliga j, “Impact of SiC on Power Devices”, in
Amorphous and Crystalline silicon Carbide IV, Springer-
Verlag, Barlin Heidelberg, pp.305-313, 1992.
[3]. Leon M. Tolbert, BurakOzpineci, S Kamrul “wide band
gap semiconductors for utiltity applications” the University of
Tennessee Knoxvile,TN 37996-2100.

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[4]. M .E .Levinshtein ,S.L. Rumyantsev , M.S .Shur,
”propertieso advanced semiconductor materials; GaN, GaAa,
AIN ,InN , BN ,SiC” ,New York; john wiley and sons, inc2000-
2001.
[5]. Deci-elec “yolo development wide band gap
semiconductorin power electronics 17&18 april 2013.
[6]. A .K. Agarwal, S.S. Mani, S. Seshadri, and J B Cassad,
P.A. Sanger and C.D. Brandit, N. Saks, SiCPower Devices,”
Naval Research Reviews, vol.51, no1. 1999.
[7]. Ned Mohan, T.M Undelend , and W.P .Robbins,
PowerElectronics 2 nd edition john willey and sons.

Sic an advanced semicondctor material for power devices

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