ELECT 871 12/01/03

SiC basic properties

• The basic properties of SiC makes it a material of choice for fabricating devices operating at high power and high temperature

Property

Band gap (eV)

Breakdown field for 1017cm-3 (MV/cm)

Saturated Electron Drift (cm/s)

Electron mobility (cm2/Vs)

Hole mobility (cm2/Vs)

Thermal Conductivity (W/cmK)

Si

1.1

0.6

107

1350

450

1.5

GaAs

1.42

0.65

1x107

6000

330

0.46

4H-SiC

3.2

3-5

2x107

<900

<120

4.9

3C-SiC

2.36

1.5

2.5x107

<800

<320

5.0

GaN

3.4

3.5

1.5x107

1000

300

1.3

6H-SiC

3.0

3-5

2.5x107

<400

<90

4.9

ELECT 871 12/01/03

SiC growth processes

B A C B A B C A

B A C B A B C A

C A B C A B C A

C A B C A B C A

B C A C B A B C A

B C A C B A B C A

B C A C B A B C A

B C A C B A B C A

B C A C B A B C A

B C A C B A B C A

B C A C B A B C A

B C A C B A B C A

C-Axis

(0001) Basal plane

Growth Surface

6H substrate polished 3-5° "Off-axis"

6H epilayerx

xx

StepTerrace

3C epilayer DPB Defect

Controlled Homoepitaxial Growth: Nucleation takes place at steps

"On- axis" (< 1° tilt) 6H substrate

Heteroepitaxial (3C) Growth: Nucleation takes place on terraces

Figure modified after Matsunami et al., Amorphous and Crystalline Silicon Carbide, Springer-Verlag, Proceedings in Physics, V. 34 (1989) pp. 34-39.

• DPB defects result from change in stacking of atomic layers in hetero-epitaxial growth

ELECT 871 12/01/03

SiC growth features

AFM image around a dislocation core in 4H-SiC

0.5 nm (two Si-C bilayers) and 1.0 nm (4 Si-C bilayers = 4H-SiC repeat distance) step features are clearly revealed around screw dislocation core.

AFM image of SiC epilayer growth showing step bunching

ELECT 871 12/01/03

SiC devices: Comparison with GaN• Mostly used for high power microwave devices (L, S, C-band

amplifiers)• Applications in high power and high temperature electronics (HEV

circuits, engine sensors, power schottky and p-n diode rectifiers etc.)• Advantages compared to GaN:

– More mature technology than GaN– Bipolar devices (Thyristors, BJTs, DIMOS much more feasible)– Native substrate available, high thermal conductivity– Easier processing than GaN

• Disadvantages compared to GaN:– Indirect bandgap material, lower mobility, no HFET– Polytypism, even native substrates have large area defects– Expensive – Growth not easy due to high temperature process

ELECT 871 12/01/03

SiC based MESFETs• Growth is easier due to lattice

matched substrate. Also higher thermal conductivity.

• Have higher input and output impedances, so easier to design broadband matching networks

• Power output up to 6-7 W/mm

• Due to lower mobility of SiC Ft usually not more than 20 GHz. (as 2DEG not possible)

• Acceptable noise figure and linearity

Small periphery (2300 m)

4H-SiC substrate(Vanadium doped)

0.25 μm p-type buffer layer Doping < 5 1015 cm-3

0.26 μm n-type channel layer Doping ~2 1017 cm-3

Layer structure

ELECT 871 12/01/03

SiC based power electronics

• 3100 V, 20 A, 62 kW-pulsed, single cell SiC Thyristors demonstrated• Advantage of SiC is much higher power operation due to wider

bandgap of SiC

N+ 4H-SiC Substrate

N+

P+

P-

N

N JTEN JTE

P+ N+ N+

AnodeGateGate

Cathode

50 m, 7-9x1014 cm-3

J3

Gate

Anode

2 m

m

Asymmetrical gate turn off thyristor structure for SiC

ELECT 871 12/01/03

SiC based schottky diode gas sensors

• Devices made from wide bandgap materials such as SiC and GaN are sensitive to gases such as H2, CO and NO2.

• The basic mechanism for such sensing is that the schottky barrier height is lowered as the gas gets absorbed by the schottky barrier.

• Very useful for fire detection, and gas sensing in high temperature environment

A SiC schottky diode for H2 gas sensing

ELECT 871 12/01/03

Few final things• The final is on 10th December starting at 9.00 a.m.

• The presentation to be determined by alphabetical sequence of the Last Name (3 on Wednesday and 3 on Friday)

• Each presentation will be 15 minutes

• The project report is due by Friday morning, 12th December (I need to submit grades by Friday).

• Good Luck!