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Printed Pages—4 EC301
B.Tech.
(SEM. IIT) ODD SEMESTER THEORY
EXAMINATION 2013-14
ELECTRONIC DEVICES
Time : 3 Hours Total Marks : 100
Note :— Attempt all Sections.
SECTION-A
1. Attempt all parts : (2*10=20)
(a)
(b)
©)
qd)
(e)
0
(g)
(h)
What do you mean by Effective Mass ? How does
it depend on Energy Band ?
Draw and explain Fermi Dirac distribution function.
What is Punch through in diode ?
What is Contact Potential and how does it vary with the
Biasing?
State difference between Phosphorescence and
Fluorescence.
Explain carrier life time. How direct recombination life time
differs from indirect recombination life time ?
Write down the maximum power delivered by solar cell.
Draw V-I characteristics of Photodiode and what is the
significance of 3" and 4" quadrant operation of
Photodiode ?
EC301/DNG-52491 1 {Turn Over (i) What is Population Inversion Layer in LASER ? Write
down the difference between stimulated emission and
spontaneous emission.
G) How a BJT is used as an amplifier and a switch ?
SECTION-B
Attempt any three parts : (3x10=30)
(a) (i) What is mobility and discuss its dependency on
temperature and doping concentration.
(ii) Derive the expression for the equilibrium carrier
concentration (n,, p,) using Fermi Dirac Distribution
Function.
(b) (i) What is Diffusion Length ? Derive its value using
continuity equation.
(ii) Discuss the relationship between Photoconductivity
and Mobility of carriers.
(c) @ Differentiate between Zener and Avalanche
Breakdown.
(ii) Derive the expression for electron current in n type
material of a forward Biased PN junction.
(d) (i) Write the special features of MESFET. Differentiate
between MOSFET and MESFET.
ii) Differentiate between Rectifying contacts and Non
Rectifying contacts with the help of Band Diagram.
(e) (i) Explain different components of current flow through
the structure of a N-P-N transistor with the help of
current flow diagram.
i) What is Photo Detector ? Explain the operation of
p-i-n photodetector. What are the suitable materials
of it ? How can it be made more sensitive to low level
intensity of light ?
EC301/DNG-52491 2
3.
SECTION-C
Note :— Attempt all questions. (5x10=50)
Attempt any two parts :
(a) Discuss temperature dependency of carrier Concentration.
(b) A semiconductor has , =-10'%/cm’, Hw, = 0.5 x 10'%/cm?
and E, = 2 eV. It is doped with 10'’/cm? donors. Calculate
e and hole and intrinsic carrier concentration at 62.7°C.
Draw its energy band diagram showing the position of. E,
(c) What is Hall Effect ? Derive the expression for Hall Angle.
Attempt any two parts :
(a) What is Quasi Fermi Level ? An n type Si sample with
H, = 10'%/cm? is steadily illuminated such that
8, = 107 EHP/cm?-s. If t, = 1, = | ps for this excitation.
Calculate the separation in the Quasi Fermi Level
(F,-F,).
(b) Write short notes on:
(i) Cathodoluminesence
Gi) Electrotuminesence.
(c) What do you mean by diffusion of carriers ? Derive
expression for Diffusion Current. Draw drift and diffusion
of electron and hole in an applied electric field.
Attempt any two parts :
(a) Derive the expression for Penetration depth X, and X, in
Nand P Region respectively for a PN jn diode. Also derive
an expression for depletion region width.
(b) What is time variation of Stored Charge ? Draw and explain
the excess hole distribution in n region as a function of time
during the transient.
EC301/DNG-52491 3 {Turn Over (©)
An abrupt Si P-N junction has p, = 10'cm” on one side
and p = 5 x 10cm on the other side.
(i) Calculate Fermi Level Position at 300 K in P and N
Regions.
Gi) Draw an equilibrium band diagram for the junction
and determine the contact potential V, from the
diagram.
6. Attempt any two parts :
(a)
(b)
(©)
What is the difference between Homojunction and
Heterojunction ? Explain Heterojunction with the help of
ideal band diagram.
For a MOSFET. Given that L,,, = 0.4 um, t, = 8 nm,
H, = 450 cm?/V-s and V, = 0.7 V. Find out C,,, K',. For a
MOSFET with W/L = 8 pm/0.8 pum, calculate the value of
Vg and Vy snin needed to operate a transistor in saturation
region with a DC current I, = 100 wA.
Explain the operation of enhancement type MOSFET and
discuss its Drain and Transfer characteristics.
7. Attempt any two parts :
(a)
(b)
(©)
Explain Ebers-Moll Model of BJT.
Write a short note on semiconductor LASER.
What is Base Width Modulation and Early effect in BIT?
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