M.Sc. (Semester (CBCS) Examination Oct/Nov-2017
Electronic Science
SEMICONDUCTOR DEVICES
Day Date: Thursday, 16-11-2017 Max. Marks: 70
Time: 10.30 AM to 01.00 PM
Instructions: Q. and are compulsory.
Answer any three questions from Q.3 to Q.7.
All questions carry equal marks.
Use of nonprogrammable calculator is allowed.
Q.1 Choose the alternatives given below. 06
lattice structure is called zinc blende structure.
Simple cubic Body centered cubic
Face centered cubic Diamond
Which is the compound or element not used in LEDs?
CaO GaP
GaAs All of the above
Band gap of silicon is at room temperature (T=300K).
0.67eV 1.1eV
2.42eV 5eV
Density-of-states effective mass of an electron in GaAs is
1.1m0 0.067m0
0.45m0 0.98m0
is voltage-variable capacitance of a reverse biased p-n junction.
Varactor diode Tunnel diode
Zener diode None of the above
Miller overlap capacitance is the capacitance between
Gate and drain Gate and shield
Gate and source Source and shield
State True or false. 08
In an electronic grade Si, the levels of impurities are reduced to parts
per billion or ppb.
The hot carrier effect implies that the carrier drift velocity is comparable
to the thermal velocity.
An Ebers-Moll model is more accurate and can handle some secondorder
effects better than the Gummel-Poon charge control model.
The absorption of light by semiconductors gives rise to useful electronhole
pairs.
The electrical conductivity of semiconductor is not as high as metal but
also not as poor as electrical insulator.
MOSFET is a current-controlled device.
Bipolar junction transistor consists of an emitter-base diode
connected back to back to a collector-base diode.
Total energy of a particle is the product of kinetic and potential energy.
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Q.2 Describe a Czochralski method for single crystal Si growth. 05
Explain what is Heteroepitaxy and misfit dislocations? 05
Distinguish between photo detectors and light emitting diodes. 04
Q.3 Discuss a Kronig-Penney model for one dimensional periodic potential. 10
Discuss the inferences drown form the E-k relationship. 04
Q.4 With a schematic band diagram, explain the carrier concentration at
equilibrium for intrinsic, n-type and p-type semiconductors with the help of
density of states and Fermi-Dirac distribution function.
10
Distinguish between n-type and p-type semiconductors. 04
Q.5 An abrupt Si p-n junction has Na 1018 cm on one side and Nd 5X1015
cm-3 on the other; Calculate the Fermi level position at 300K in the p and
n regions. ii) Draw an equilibrium band diagram for the junction and
determine the contact potential, V0.
08
Discuss etching process in fabrication of p-n junctions. 06
Q.6 Explain in brief the GaAs MESFET and a high electron mobility transistor. 10
Explain switching operation of BJT using neat diagram. 04
Q.7 Explain the quantum mechanical tunneling of electrons through a potential
barrier in a tunnel diode.
10
Write a note on solar cell. 04