Microelectronic & optoelectronic quastion of 2007 ,4th sem ECE ,WBUT

Microelectronic and optoelectronic 2007 ,wbut 4th semester
GROUP-B
2. Derive the one dimensional continuity equation for minority carriers in generation recombination process, under low injection condition.Gn, GP, Rn and Rp are generation and recombination rates for electron/hole.
3. What is population inversion in laser? What is external quantum efficiency in a semiconductor laser? What is the optical feedback and oscillation by which the amplified coherent emission is obtained?
4. An n-type semiconductor at thermal equilibrium(T=300K) has a linear variation in doping concentration given by Nd(x)=1016-1919x, 0≤x≤1µm.Determine induced electric field. (volt equivalent temperature at room temperature =0.02V)
5. Discuss the principle of operation of vertical power BJT.
6. With energy band diagram describe schottky junction barrier formation . Describe its operation under external bias.
GROUP-C
7. (a) What is SCR? point out its major uses.
(b0 By using two transistor analog, briefly describe the operation of two terminal scr.
(c) Is it possible to observe the purpose of SCR by connecting two transistors? Explain.
(d) How does the presence of third terminal control the I-V response of SCR? Explain with system diagram.
8. (a) Sketch the ideal energy band diagram of a metal-semiconductor junction in which Фm<фs. Explin why this is an ohmic contact.
(b) Discuss how 2D-electorn gas is formed ain semiconductor heterojuction.
(c) the schottky barrier of a Si schottky junction is фBN=0.59v,the effective Richardson is A=111A/K2-cm2 and the crosssection area is a=10-4cm2
for T=100k, calculate
(i) Ideal reverse saturation current
(ii) The diode current for V (applied)=0.30V.
9. (a) Illustrate the basic process flow in micromanaging? What do you mean by optical lithography?
(b) What do you mean by plasma etching?
(c) Explain one non-lithographic microfabrication technology.
10. (a) What is the advantage of optical fibre over the copper wire system ?
(b) What is the difference between step index and graded index fibres?
(c) Distinguish between non-radiative and radiative recombination processes in a semiconductor .Express the internal quantum efficiency in terms of the life times of the process.
(d) Asilican optical fiber has a core refractive index of 1.5 and the cladding refractive index of 1.450 . calculate
(i) the critical angle for the core cladding interface.
(ii) the acceptance angle in air for fiber .
(iii) the nimerical aperture (NA) of the fiber.
11. Write short note on any three of the following
(a) Solar cell
(b) semiconductor laser
(c) Insulated bipolar junction transistor
(d) P-I-N photodiode
(e) O.E.I.C.