ECE 315 Quiz 2 Solution
Fall 2005
Diode equations in case:
W
d
= x
n
+ x
p
bi
D
A
si
V
N
N
q
+
=
1
1
2
0
ε
ε
, N
A
x
p
= N
D
x
n
,
2
i
D
A
bi
n
N
N
q
kT
V
=
,
ε
si
is the relative dielectric constant of silicon,
D
n
the electron diffusivity,
τ
n
the recombination
lifetime,
k
B
the Boltzmann constant, and
T
the temperature (default=300K).
1.
The depletion region width
W
d
in a
p
+
n
junction (with the p side doping of
N
A
and the side doping of
N
D
and
N
A
>> N
D
) is on the order of which length scale in the semiconductor: (15 pts)
(a)
3
D
N
(b)
3
A
N
(c)
The diffusion length of electrons as
defined by
n
n
n
D
L
τ
=
(d)
The diffusion length of holes as
defined by
p
p
p
D
L
τ
=
(e)
L
n
+ L
p
as defined above.
(f)
The Debye length in the nregion as
defined by
D
B
si
Dn
N
q
T
k
L
2
0
ε
ε
=
(g)
The Debye length in the pregion as
defined by
A
B
si
Dp
N
q
T
k
L
2
0
ε
ε
=
(h)
Dp
Dn
L
L
(f)
2.
For a semiideal nMOSFET, estimate the necessary gate voltage to turn off the ON current
by 8 orders of magnitude (10
8
) at the room temperature: (a) 26mV, (b) 0.1V, (c) 0.5V, (d)
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 Fall '07
 SPENCER
 Microelectronics, load line, VO VTC

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