semiconductor devices 27 - university of yorkah566/lectures/semi... · 3 realistic schottky barrier...
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Department of Electronics
Semiconductor Devices 27
Atsufumi Hirohata
11:00 Thursday, 4/December/2014 (P/T 005)
Exercise 6
Calculate the depletion layer capacity at a reverse bias
VR = 0.5 V in a Au/n-Si Schottky diode. Assume the
following parameters:
Au work function: φM = 4.80 eV
n-region: doping density of ND = 1 × 1021 m-3
Si electron affinity: χ = 4.05 eV
Si Fermi level: EF = EC – 0.15 eV
permittivity: ε = ε × ε0 = 12.0 × 8.854 × 10-12 F/m
and q = 1.6 × 10-19 C.
q(Vbi + VR )
Depletion layer
EF
qVR EC
EV
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Answer to Exercise 6
The built-in potential can be calculated as
For an n-type contact,
qVbi = !B ! EC !EF( )
!B = !M ! "!M > "
!M < " : ( ) contact
: ( ) contact with the barrier height of
Hence,
qVbi = !M ! !( )! EC !EF( )By substituting the given parameters,
qVbi = 4.80! 4.05( )! 0.15= 0.60 eV[ ]
C = !w=
q!ND
2(Vbi +VR )
Depletion layer capacity C is
=1.6!10"19 #12.0!8.854!10"12 #1!1021
2(0.60+ 0.5)
=1.70!10"8
1.3=1.14!!10"4 C[ ]
#1.1!10"4 C[ ]
27 Metal Oxide Semiconductor Junction
• Bias application
• Surface space-charge
• MOS FET
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Realistic Schottky Barrier Image force and Shottky barrier :
* S. M. Sze, Physics of Semiconductor Devices (Wiley, New York, 2006).
Metal Oxide Semiconductor Junction
n-type semiconductor at V = 0 :
* S. M. Sze, Physics of Semiconductor Devices (Wiley, New York, 2006).
p-type semiconductor at V = 0 :
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Metal Oxide Semiconductor (MOS) p-type Si / SiO2 / poly-Si :
* http://www.wikipedia.org/
In 2007, Intel introduced p-type Si / high-k oxides (HfO2 etc.) / metal.
Bias Applications Reverse bias ( ) :
* S. M. Sze, Physics of Semiconductor Devices (Wiley, New York, 2006).
Forward bias ( ) :
Forward bias ( ) :
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Surface Space-Charge
p-type semiconductor :
* S. M. Sze, Physics of Semiconductor Devices (Wiley, New York, 2006).
Space-Charge Variation
With different surface potentials ΨS :
* S. M. Sze, Physics of Semiconductor Devices (Wiley, New York, 2006).
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Charge Distributions
Band diagram of a metal oxide semiconductor junction under an inversion condition :
* S. M. Sze, Physics of Semiconductor Devices (Wiley, New York, 2006).
Charge distributions :
Electric field distributions :
Potential distributions :
MOS Field Effect Transistor (FET) One of the most popular transistors for amplification and switching :
* http://www.wikipedia.org/
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MOS FET Operation
Current-Voltage characteristics :
* http://www.wikipedia.org/
MOS FET Operation
Gate functionality :
* https://www.youtube.com/watch?v=DquJSQasWG0