West Bengal Institute of Technology (WBIT) 2011-4th Sem B.Tech Electronics and Communications Engineering B_TECH ,Microelectroics and optoelectronics devices(ME),,ester,WBUT - Question Paper

2. Derive the one-dimensional continuity formula for minority carriers in generation recombination process under low injection condition. 5
3. What is Heterojunction? How many kinds of heterojunctions are possible? Draw the band diagrams of every kind of heterojunction? 1+1+3
4. Sketch an n-p-n darlinton pair configuration and discuss hoe the effective current gain can be increased by this configuration over that in power BJT. 2+3
5. define the operation of a CCD with suitable diagram. 5
6. a) elaborate population inversion in laser and external quantum efficiency in a semi-conductor laser?
b) What os a optical feedback and laser oscillation by which the amplified coherent emission is obtained?
(1+1)+3



GROUP-C
( Long ans kind questions)
ans any 3 of the following: 3*15=45


7. a) What is a bipolar transport? Why carrier generation and recombination rate are identical in thermal equilibrium?
b) Derive the 1 dimensional continuity formula for minority charge carriers in generation process,
under low injection condition. Gn, Gp, Rn and Rp are generation recombination rates for electrons/holes.
c) define the EINSTEIN formula and also prove it?
d) What do you mean by surface effect?
5+4+3+3

8. a) define the short channel effect of a MOSFET.
b) What do you mean by Subthreshold conduction of a MOSFET?
c) Show the schematic structure and operation of typical LED. elaborate the applications of LED?
d) explain the principle of operation of vertical power BJT.
5+2+5+3

9. a) What is SCR? Point out its major uses.
b) By using transistor analogy briefly define the basic operation of 2 terminal SCR.
c) Is it possible to observe the purpose of SCR by connecting 2 separate transistor? discuss.
d) How does the presence of the 3rd terminal controls the I_V response of SCR? discuss with system diagram.
e) define the various turn on & turn off mechanism of an SCR.
2+3+2+4+4

10. a) What do you mean by MEMS?
b) discuss 1 lithographic micro fabrication technology.
c) define the isotropic and Anisotropic etching. What do you mean by plasma etching?
d) define the surface an Bulk Micro-machining to design the pressure sensor.
1+3+5+6


11. Write short notes on any 3 of the following: 3*5
a) Rectifying Contact.
b) Bulk micro-machining in MEMS.
c) Surface emitting LED.
d) Solar cells.
e) MOSFET Scaling.
f) IGBT.

Earning:   Approval pending.