Environmental Engineering Reference
In-Depth Information
Figure 1.7
Schottky barrier formation at a metal/n-type semiconductor
when an ideal interface is formed between the two materials.
the
φ
b
formed at this interface is given by:
φ
b
=
φ
m
−
χ
(1.1)
The formation of potential barriers at the metal/p-type semicon-
ductor is very similar, but the band bending will be in the opposite
direction,formingpotentialbarriersfortheflowofholes.Theabove
descriptionisvalidonlyforidealinterfaces,butthesituationisvery
different for interfaces strongly affected by semiconductor defects,
surfaceorinterfacestates.Inthesesituations,theFermilevelwillbe
pinnedbythedefectstatesandhence
φ
b
isindependentofthemetal
used for the formation of the electrical contact. The drastic effects
of Fermi-level pinning will be discussed in detail in later chapters of
this topic.
The nature of the potential barrier formed at the MS interface
will govern the electrical properties of this interface. If the
φ
b
is in
excess of
∼
0.40 eV and the width of the depletion region (
W
)is
considerable, the interface will have rectifying electrical properties
described by Eq. 1.2 [13, 14].
·
exp
−
e
φ
b
kT
exp
eV
nkT
−
1
I
D
=
SA
∗
T
2
(1.2)
where
I
D
=
Electric current in dark condition
=
S
Area ofthe contact
A
∗
=
Richardson constant for thermionic emission
T
=
Temperature in Kelvin
