
Principles of Analog Electronics
278
These conditions allow us to rewrite the Maxwell–Boltzmann distribution as
n
n
e
n
p
kT
bi D
0
=
−
⇒ nne
pp
V
D
T
0
0
()
=
where
VkTq V/
T
is dened as the thermal voltage, that is, an electrostatic
voltage across the junction.
Observation
Let us determine the value of
T
at room temperature (20°C):
)
(
==
+
≅
−
−
V
kT
q
1.38*1 0 273.16 20
1.6*10
25.3
T
23
19
We must underline that it is not always a negligible value.
Keeping in mind the expression of the density of diffusion current and combin-
ing the last equations:
JqD
dn
dx
qD n
L
e 1
n
x
n
p
x
np
n
v
V
0
0
0
D
T
==−
=
=
JqD
dp
dx
qD p
L
e 1
p
x
n
n
x
pn
p
v
V
0
0
0
D
T
=−
=
=
The diffusion current of minor ...