PG – 518

*PG518*

II Semester M.Sc. Degree Examination, July/Aug. 2013 Electronic Science EL 204 : HIGH POWER DEVICES Time : 3 Hours

Max. Marks : 80

Instructions : Section – A : Answer all questions. Section – B : Answer any four questions. SECTION – A 1. Define the following : a) Space charge limited current b) Life time of a charge c) Gain-bandwidth product d) Ohmic contact.

(5×4=20)

2. Distinguish between power transistor and ordinary transistor. 3. Explain double injection process. 4. Explain the VMOS structure. 5. Explain the neutron doping process. SECTION – B 6. a) Distinguish between latching and holding currents and hence derive an expression for a holding current of a thyristor. b) What is a linearly graded junction ? Obtain an expression for the breakdown voltage for a linearly graded junction. 7. a) Explain how field plate and floating field ring are used to reduce electric field crowding at the edges. b) Define, conductivity modulation in power BJT and hence derive an expression for potential drop in this region. 8. a) Distinguish between the turn-on and turn-off process of a thyristor. b) Explain the structure and operation of JFET. c) Obtain an expression for drain current in power JFET.

8 7 8 7 4 6 5

P.T.O.

*PG518*

PG – 518

9. a) Explain the switching performance of MOSFET. b) Explain, double diffused epitaxial process. Why this process is used in transistor fabrication ? 10. a) Explain, electron irradiation process. Why it is used in the fabrication of power devices ? b) Explain, surface passivation and encapsulation techniques used in the fabrication of power devices. 11. Explain any three of the following : a) Avalanche breakdown b) Surface contouring technique c) PIN diode d) DMOS e) Insulated gate rectifier. _______________________

7 8 7 8

(3×5=15)