This document discusses metal-semiconductor contacts, including Schottky and ohmic contacts. It provides energy band diagrams to illustrate how Schottky and ohmic junctions work. Schottky contacts form a rectifying barrier between a metal and lightly doped semiconductor. Ohmic contacts have a low resistance non-rectifying junction between metal and heavily doped semiconductor. The document discusses the advantages of Schottky diodes for applications such as RF mixing and solar cells due to their higher current and frequency performance compared to PN junction diodes. Ohmic contacts are used where low resistance contact is needed to allow easy flow of charge carriers.

1. Metal-Semiconductor
Contacts
Kasif Nabi
imi2015007
Department Of Microelectronics
Indian Institute Of Information Technology Allahabad
2nd November
2 November 2015 1

2. Metal-Semiconductor Contacts
 Schottky Contacts
• Metal on lightly doped silicon
• Rectifying
 Ohmic Contacts
• Metal on heavily doped silicon
• low resistance
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3. How Schottky Junction Works ?
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Energy band diagram of an isolated metal adjacent to an
isolated n-type semiconductor
metal n type semiconductor
Fm = Work Function of metal
Fs = Work Function of
semiconductor
c = Electron Affinity of Si

4. How Schottky Junction Works …..
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Energy band diagram of a metal-n semiconductor contact in
thermal equilibrium
qFb =
qFb = q (Fm – c)
Schottky barrier
height

5. How Schottky Junction Works …..
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Energy band diagram of a metal-n semiconductor contact in
thermal equilibrium
qFb =
qFb = q (Fm – c)
Schottky barrier
height

6. How Schottky Junction Works …..
• is the barrier against the electron
flow between metal and SC.
Fb
•
• Fbp is the barrier against the hole flow
between metal and SC.
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Fbn
Energy band diagram of a metal–semiconductor contact
N type SC P type SC

7. Measurement of barrier potiential fB
and working of schottky contacts
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N type SC
N type SC
Under thermal equlibrium
Under reverse bias

8. Working of Schottky contacts…
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-
N type SC
Under farword bias

9. Schottky diode
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10. Advantages and application of Schottky
Diode
 Advantage
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• I0 of a Schottky diode is much larger than a PN junction diode,
depending on fB .
•A larger I0 means a smaller forward drop V.
• Schottky diodes can operate at higher frequencies than PN
junction diodes
 Application
• RF mixer and detector diode
• Solar cell applications
• Voltage clamping devices
• A Schottky diode is the preferred rectifier in low voltage, high
current applications

11. Ohmic contacts
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 The Ohmic contact is a low resistance junction (non-rectifying) provides current
conduction from metal to semiconductor and vice versa.

12. How Ohmic Contact Works ?
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ideal energy band diagram before contact
n type
after contact for a metal –n+ semiconductor
junction
Metal n+ type SC
Metal n+ type SC

13. How Ohmic Contact Works….
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Under forward bias condition Under reverse bias conditon
Positive bias in the metal part was
applied, and they will feel no barrier
A negative bias forces electrons to flow from
metal to semiconductor seeing a very small
barrier

14. Advantage and application
Low resistance ohmic contacts are used to
allow charge to flow easily in both directions.
The RC time constant is much better because
of low resistance of contact.
Shows better frequency response of device
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15. References
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 https://www2.warwick.ac.uk/fac/sci/physics/current/postgraduate/regs/mpags
/ex5/devices/hetrojunction/ohmic/
 Silicon VLSI technology by (Plummer ,Deal and griffin)
 https://en.wikipedia.org/wiki/Metal–semiconductor_junction

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