OUTLINE

1
Lecture 7

• OUTLINE
• Poissons equation
• Work function
• Metal-Semiconductor Contacts
• Equilibrium energy band diagrams
• Depletion-layer width
• Reading Pierret 5.1.2, 14.1-14.2 Hu 4.16

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Poissons Equation
area A
Gauss Law
E(x)
E(xDx)
Dx
?s permittivity (F/cm) ? charge density
(C/cm3)
EE130/230M Spring 2013
Lecture 7, Slide 2
3
Charge Density in a Semiconductor

• Assuming the dopants are completely ionized
• r q (p n ND NA)

EE130/230M Spring 2013
Lecture 7, Slide 3
4
Work Function
E0 vacuum energy level
FM metal work function
FS semiconductor work function
EE130/230M Spring 2013
Lecture 7, Slide 4
5
Metal-Semiconductor Contacts

• There are 2 kinds of metal-semiconductor
  contacts
• rectifying
• Schottky diode
• non-rectifying
• ohmic contact

EE130/230M Spring 2013
Lecture 7, Slide 5
6
Ideal M-S Contact FM gt FS, n-type
Band diagram instantly after contact formation
qVbi FBn (Ec EF)FB
Equilibrium band diagram
n
Schottky Barrier Height
W
EE130/230M Spring 2013
Lecture 7, Slide 6
7
Ideal M-S Contact FM lt FS, n-type
Band diagram instantly after contact formation
Equilibrium band diagram
EE130/230M Spring 2013
Lecture 7, Slide 7