National
I
nstitute
of
Techno
I
og1,,.
K
u
ruksh etra
Theory
Exanr
ination. November
20
I
2
Number
of
pages
used:
Two
Programme:
B.Tech. ECE
Subject:
Semiconductor Devices
and
ApplicarionsTime
Allowed:
Three
hours
Note:
Attempt FIVE
questions
in
atl
selecting
at
least
one
qr.iiini,
r.o;,
h
f
the
four
units.
UNI'I'I
The
resistivities
of
pregion
and nregion
of
a stepgraded
ce
diocle are
2 f)cm
and
I
f)cm
respectively. Determine the height
ol'thc
potential energy
barrier.
Given:
rp:
1800 cm2/VS,
p,:
3800
crn]/Vr,
n,
,..
2.5
*
10,,
/crni.
slrribols
used
carry
usual meanings.
What
are
drift
and
diffusion
currents
in
semicondLrctors'l
Shorv
that the
injected
minority
carrier current under
low
level
iniection
is
essentiallv
diffusion
uri.nt.
Derive
the
mathematical expression
for
semiconductor
cliocle cLu.rerlt.
Analyze the
effect of
temperature
on
forbiciden
encrgy
gap
ancl
nrobilitv of
charge
carridrs in semiconductors.
Draw and
explain
diode.
How
pn
junction
diode can be
used as
an
electrorric switch?
With
the help
of
appropriate
waveforms. explain diode
reverse
recoverv iinrc.
Fora
centre
tap
l'ullwave
r:ectifier.
derive
the
exprcssions firr
thc
lollowing:
(i)
average
current
(ii)
dc
output
voltage
(iv)
rectifier
efficiency
(v)
ripple
factor
In
the
circuit
shown
in
Fig.
l.
the
avalanche diocle rcsularcs
at 50
V
over
the
range
of
diode
currents
from
5
to
40
mA.
Dcterrninc
[l
ts
allow
voltage
regulation
from a
load current
ls= 0
upto
1,,,,.
tlre maxinrunr possible value
of
i1.
Also calculate
l,nr*.
R
TJNI'I ITcharacteristics
of
an
ideal
diocle
and
a
Semesterlll
Course
no. ECT
201
Max Marks:50
{
Ir
(b)2(a)
(b)
3(a)
(b)
a@)
(b)
Rt
s(a)
(b)
6(a)(b)
UNITITI
Give the EbersMoll
rnodel
{or a
prrp transistor
with
proper labels and
write
down the
junction
voltages
as
lunctions
ol
currents.
Also
show
that
CEcharacteristics
do not
pass
through
the
srcin.
Draw
tlie
hparameter rnodel
of
bipolar
junction
transistor
at
low
fiequency
and
derive theexpression
tbr
voltage gain.
Draw the
electrical
circuit
diagram
of
the emitter follower and explain
its
operation.
Also
nrention its inrportattt
fbaturcs.
For the
circuit
shorvn
in ljig.2
determine the
value
of
V1p.
Frz'z
Draw the
commonsource
drain
characteristics
of
an
nchannel
FET. How
will
you
determine tlre pinchol'
voltage?
In the
circuit
shown
in
the Fig.3. the
amplifier
stage
uses
an
n^channel FET
with
Ioss
=
lmA,
Vp

l
V.
cluiescent
drain to ground voltage
= l0
V.
Determine
R1.
Symbols
used
carry
usual
nreanings.
7(a)
(b)
8(a)
(b)
Fiq.3
J
Show
the constructional details
of
an enharlcement
type
MOSFF.['.
Also draw
itsdrain
characteristics
and transfbr curves
and
explain
tlrose.
Give the
structure and ecluivalent
circuit
of
MOSFE1'
capacitor
and
discuss
itscharacteristics
t'eatures
lo'n:t
UNI'TIV