AMIETE – ET (OLD SCHEME)
Code: AE25 Subject: PHYSICAL ELECTRONICS AND SOLID STATE DEVICES
Time: 3 Hours
Max. Marks: 100
NOTE: There are 9 Questions in all.
· Question 1 is compulsory and
carries 20 marks. Answer to Q.1 must be written in the space provided for it in
the answer book supplied and nowhere else.
· Out of the remaining EIGHT
Questions answer any FIVE Questions. Each question carries 16 marks.
· Any required data not
explicitly given, may be suitably assumed and stated.
Q.1 Choose
the correct or the best alternative in the following: (2
10)
a. With the increase in the
temperature of the intrinsic semiconductor
(A) energy of the
atom increases
(B)
holes are generated in the conduction band
(C) resistance of the semiconductor increases
(D) atomic radius decreases.
b. The Fermi-Dirac statistics is based on
(A)
electron
and photons
(B) photons and protons
(C) electrons and holes
(D) gas molecules
c. The energy required to dislodge electrons from n type Si is
(A) 0.05 eV
(B) 0.5 eV
(C) 5.0 eV
(D) 50.0 eV
d. The reverse saturation current ICO of Si diode varies as
(A)
T2 (B) T3
(C) 
(D) 
e. A Schottky diode has
(A) a large voltage drop than that
of an ordinary diode .
(B) good
ohmic resistance
(C)
a
negligible storage time.
(D)
due
to minority charge carriers.
f. In a MOSFET, the threshold voltage can be lowered by
(A) increasing the gate oxide
thickness
(B) reducing the substrate concentration
(C) increasing the substrate concentration
(D) using the dielectric of lower constant
g. The efficiency of an LED for generating light is directly proportional to the
(A)
temperature (B) voltage applied
(C) level of doping used (D)
current injected
h. The fill factor for the solar cells is approximately
(A) 0.2 (B) 0.1
(C) 0.7 (D) 1.0
i. The Hall coefficient for a particular material was found to be zero. The material is
(A) metal (B) intrinsic semiconductor
(C) insulator (D) extrinsic
semiconductor
j. Varactor diode has variable
(A) Resistance (B) Capacitance
(C) Inductance (D) None
of above
Answer
any FIVE Questions out of EIGHT Questions.
Each
question carries 16 marks.
Q.2 a. How does the conductivity or resistivity of
the semiconductor materials vary with temperature? Do metals also exhibit the
same behaviour? (8)
b. Differentiate between
direct band gap and indirect band gap semiconductors with examples. (8)
Q.3 a. A silicon semiconductor has the intrinsic
carrier concentration of 1016 m–3 and donor density 1020
m–3. Extra carriers are produced in the semiconductor by the process
of injection. If the extra carrier density at a point is equal to 1018
m–3, determine the ratio of
hole concentration to electron concentration at that point. Also estimate the
percentage increase in p and n resulting from injection? (8)
b. Explain Hall
effect and discuss its application for semiconductor. (8)
Q.4 a. How rectifying contacts differ from ohmic
contacts. Explain with examples. (8)
b. A Zener diode has ND = 1020
m–3 and NA = 1023 m–3. Avalanche
breakdown occurs in the diode when the electric field reaches 107 Vm–1.
Calculate the breakdown voltage. Assume 
to be 10–10 Fm–1. (8)
Q.5 a. Explain
following terms for Bipolar transistors. (8)
(i)
Emitter injection 
(ii) Current crowding
(iii)
Kirk effect (iv) Base transport factor
b. Discuss briefly switching action in BJT. (8)
Q.6 a. Explain subthreshold operation of MOSFET and draw its characteristics. (8)
b. Discuss briefly various short channel effect
present in small geometry MOS devices (8)
Q.7 a. What are the limiting conditions of a solar
cell? Explain measures to improve the efficiencies of solar cells. (8)
b. Explain the working of Gunn diode and write
its applications.
(8)
Q.8 a. Discuss with the help of figures, wafer
preparation. How it differs from crystal
growth? (8)
b. Explain Hybrid
circuits. How these are different from
monolithic circuits? (8)
Q.9 Write short notes (Any FOUR) (44)
(i) Band to band tunneling (ii) Semiconductor Lasers
(iii)
CMOS Latch up (iv) Photodetectors
(v)
Heterojunctions (vi) Charge transfer
Device