Processing and Characterization of Silicon Carbide (6H- and 4H-SiC) Contacts for High Power and High Temperature Device Applications

  • Lee S
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Abstract

Silicon carbide is a promising wide bandgap semiconductor material
for high-

temperature, high-power, and high-frequency device applications. However,
there are

still a number of factors that are limiting the device performance.
Among them, one of

the most important and critical factors is the formation of low resistivity
Ohmic

contacts and high-temperature stable Schottky diodes on silicon carbide.



In this thesis, different metals (TiW, Ti, TiC, Al, and Ni) and different
deposition

techniques (sputtering and evaporation) were suggested and investigated
for this

purpose. Both electrical and material characterizations were performed
using various

techniques, such as I-V, C-V, RBS, XRD, XPS, LEED, SEM, AFM, and SIMS.



For the Schottky contacts to n- and p-type 4H-SiC, sputtered TiW Schottky
contacts

had excellent rectifying behavior after annealing at 500

o

C in vacuum with a thermally

stable ideality factor of 1.06 and 1.08 for n- and p-type, respectively.
It was also

observed that the SBH for p-type SiC (fBp) strongly depends on the
choice the metal

with a linear relationship fBp = 4.51 – 0.58fm, indicating no strong
Fermi-level pinning.

Finally, the behavior of Schottky diodes was investigated by incorporation
of size-

selected Au nano-particles in Ti Schottky contacts on silicon carbide.
The reduction of

the SBH is explained by using a simple dipole layer approach, with
enhanced electric

field at the interface due to the small size of the circular patch
(Au nano-particles) and

large difference of the barrier height between two metals (Ti and
Au) on both n- and p-

SiC.


For the Ohmic contacts, titanium carbide (TiC) was used as contacts
to both n- and p-

type 4H-SiC epilayers as well as on Al implanted layers. The TiC contacts
were

epitaxially deposited using a co-evaporation method with an e-beam
Ti source and a

Knudsen cell for C60, in a UHV system at low substrate temperature
(500

o

C). In

addition, we extensively investigated sputtered TiW (weight ratio
30:70) as well as

evaporated Ni Ohmic contacts on both n- and p-type epilayers of SiC.
The best Ohmic

contacts to n-type SiC are annealed Ni (> 950o

C) with the specific contact resistance of

» 8´10-6

Wcm2

with doping concentration of 1.1 ´10-19

cm-3

while annealed TiW and

TiC contacts are the preferred contacts to p-type SiC. From long-term
reliability tests

at high temperature (500

o

C or 600

o

C) in vacuum and oxidizing (20% O2/N2) ambient,

TiW contacts with a platinum capping layer (Pt/Ti/TiW) had stable
specific contact

resistances for > 300 hours.

Author-supplied keywords

  • Ohmic and Schottky contacts
  • Schottky barrier height lowering
  • and TLM structures.
  • capacitance-voltage measurement
  • co-evaporation
  • current- voltage
  • nano-particles
  • power devices
  • silicon carbide

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Authors

  • Sang-Kwon Lee

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