540
21 Diodes
Fig. 21.21 a Forward and
b reverse I –V
characteristic of a Au/Si
Schottky diode at 77 K.
The doping concentration
of the Si was
N D = 8 × 10 18 cm −3 .
Adapted from [1684]
(a)
0
0.2 0.4 0.6
10
-9
10
-8
10
-7
10
-6
10
-10
10
-5
10
-4
10
-3
Au/Si
N =8 10 cm
D
18
-3
00
Au/Si
N =8 10 cm
D
18
-3
(b)
5
.
1
0
0.5
1.0
10
-9
10
-8
10
-7
10
-6
10
-5
10
-4
10
-3
(V -V) (eV )
bi
-1/2
-1/2
log
10
j
V -V
bi
Fig. 21.22 Temperature
dependence of E 0 of an
Au/GaAs diode with
N D = 5 × 10 17 cm −3 . The
solid line is the theoretical
dependence for thermionic
emission according to
(21.69) with
N D = 6.5 × 10 17 cm −3 and
m ∗ = 0.07. Adapted
from [1684]
E 00
0
2 0
0
3
0
4
10
kT (meV)
10
0
30
20
40
E (meV)
0
Au/GaAs
N =5 10 cm
D
17
-3
A Schottky diode can suffer from non-idealities such as series and parallel ohmic resistance [1725].
These effects are discussed in some detail below for pn diodes in Sect. 21.4.4 and apply similarly to
Schottky diodes.
21.2.6 Ohmic Contacts
Although an ohmic contact does not have a diode characteristic, it can be understood from the previous
remarks. An ohmic contact will have a small contact resistance for both current directions. The voltage
drop across the contact will be small compared to the voltage drop in the active layer (somewhere else).
Details on electric contacts can be found in [1734].
The contact resistance R c is defined as the differential resistance at V = 0
R c =
∂ I
∂ V
−1
V =0
.
(21.70)