ELECT 871: Advances in Semiconductor Devices

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Transcript ELECT 871: Advances in Semiconductor Devices

SiC basic properties

Property Band gap (eV) Breakdown field for 10 17 cm -3 (MV/cm) Saturated Electron Drift (cm/s) Electron mobility (cm 2 /Vs) Hole mobility (cm 2 /Vs) Thermal Conductivity (W/cmK) • The basic properties of SiC makes it a material of choice for fabricating devices operating at high power and high temperature Si 1.1

0.6

10 7 1350 450 1.5

GaAs 1.42

0.65

1x10 7 6000 330 0.46

GaN 3.4

3.5

1.5x10

7 1000 300 1.3

3C-SiC 2.36

1.5

2.5x10

7 <800 <320 5.0

4H-SiC 3.2

3-5 2x10 7 <900 <120 4.9

6H-SiC 3.0

3-5 2.5x10

7 <400 <90 4.9

ELECT 871 12/01/03

SiC growth processes

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

DPB Defect

B A C B A B C A

x x x

C A B C A B C A C-Axis C A B C A B C A Controlled Homoepitaxial Growth: Nucleation takes place at steps B C A C B 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 6H epilayer Growth Surface Terrace (0001) Basal plane Step 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 of SiC epilayer growth showing step bunching 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.

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 Layer structure

0.26 μm n-type channel layer Doping ~2

10 17 cm -3

matched substrate. Also higher

0.25 μm p-type buffer layer Doping < 5

10 15 cm -3

thermal conductivity.

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

4H-SiC substrate (Vanadium doped)

Small periphery (2  300  m) • Power output up to 6-7 W/mm • Due to lower mobility of SiC F t usually not more than 20 GHz. (as 2DEG not possible) • Acceptable noise figure and linearity ELECT 871 12/01/03

SiC based power electronics

Gate

Asymmetrical gate turn off thyristor structure for SiC

Anode Gate

P +

Gate

N + N + N N JTE P 50  m, 7-9x10 14 cm -3 P + N + N + 4H-SiC Substrate N JTE J 3

Cathode Anode

• 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 ELECT 871 12/01/03

A SiC schottky diode for H 2 gas sensing

SiC based schottky diode gas sensors

• Devices made from wide bandgap materials such as SiC and GaN are sensitive to gases such as H 2 , CO and NO 2 . • 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 ELECT 871 12/01/03

Few final things

• The final is on 10 th 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, 12 th December (I need to submit grades by Friday).

• Good Luck!

ELECT 871 12/01/03