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MU Electronics Engineering (Semester 3)
Electronic Devices
May 2015
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

1 (a) What are non-ideal effects in BJT? Explain any one non-ideal effect in BJT.
5 M
1 (b) Determine the ideal reverse saturation current density in silicon p_N diode at 300°k Given Na=Nd=1016 cm-3, ni=1.5×1010cm-3
5 M
1 (c) With neat diagram explain the operation of UJT relaxation oscillator.
5 M
1 (d) Compare photo diode with phototransistor.
5 M

2 (a) Draw energy band diagram of P-N Junction for zero, forward, reverse bias clearly showing junction diagram, depletion width, fermi energy level and barrier potential.
10 M
2 (b) calculate the theoretical barrier height, built in potential barrier and maximum electric field in a metal semiconductor diode for zero applied bias consider a contact between tungsten and a type silicon doped to Nd=1016cm-3 at T=300k.
The metal work function for tungsten is ϕm=4.55V and electron a affinity for silicon is x=4.01V.
Nc=2.8×1019 cm-3, K=1.38×10-23J/K, εs=11.7×8.85×10-14, e=1.6×1019c.
10 M

3 (a) Calculate the threshold voltage VTO at VSB for a polysilicon gate n channel MOS transistor with the following parameters-
substrate doping density NA=1016 cm-3 polysilicon gate doping density ND=2×1020 cm-3 gate oxide thickness tox=500A° oxide Interface fixed charge density NOX= 4×1010 cm-2.
10 M
3 (b) Derive the drain current equation ID for MOSFET in ohmic and saturation regions.
10 M

4 (a) Draw and explain construction, working characteristics of JFET. Explain frequency limitation factors.
10 M
4 (b) Explain schottky effect. Derive the position of maximum barrier Xm.
10 M

Draw and explain, Construction and working of:
5 (a) (i) HEMT (MODFET)
5 M
5 (a) (ii) MESFET
5 M
Explain basic structure and characteristics of:
5 (b) (i) SCR
5 M
5 (b) (ii) DIAC
5 M

Solve any four of the following:
6 (a) Draw and explain Ebers-moll model of transistor.
5 M
6 (b) With the help of circuit diagram and characteristics explain application of zener diode as a voltage regulator.
5 M
6 (c) What are optocouplers? Explain any one application of optocoupler.
5 M
6 (d) Sketch and explain V-I and C-V characteristics of MOSFET.
5 M
6 (e) Explain channel length modulation with cross section of MOSFET. Write equation associated with this effect.
5 M

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