Anna University Chennai 2005 B.E PHYSICAL ELECTRONICS AND SOLID STATE DEVICES - Question Paper
Sunday, 24 February 2013 12:00Web
Code: A-25
Time: three Hours Subject: PHYSICAL ELECTRONICS AND SOLID STATE DEVICES
Max. Marks: 100
NOTE: There are 11 ques. in all.
ques. one is compulsory and carries 16 marks. ans to Q. 1. must be written in the space given for it in the ans book supplied and nowhere else.
ans any 3 ques. every from Part I and Part II. every of these ques. carries 14 marks.
Any needed data not explicitly given, may be suitably presumed and said.
_____________________________________________________________________Q.1 select the accurate or best option in the following: (2x8)
a. Junction capacitance is related with barrier potential as
(A)
(C) C = KV (B)
(D)
b. The reverse saturation current I of Si diode varies as
(A) T2
(C)
(B) T3
(D)
c.
For quiet reception the front end of FM tuner contains
(A BJT
(C) UJT
(B) FET
(D) SCR
d. .If the reverse bias in a FET is increased, its gm will
(A) increase.
(C) not be affected.
(B) reduce.
(D) suddenly fall to zero.
e. The biggest advantage of the TRAPATT diode over the IMPATT diode is its
(A) lower noise.
(C) ability to operate at higher frequencies.
(B) higher efficiency.
(D) lesser sensitivity to harmonics.
f. The tunnel diode
(A) has a tiny hole through its centre to facilitate tunnelling.
(B) uses a high doping level to give a narrow junction.
(C) is a point-contact diode with a very high reverse resistance.
(D) works by quantum tunnelling exhibited by gallium arsenide only.
g. Communication lasers are used with optical fibers, rather that in open links, to
(A) ensure that the beam does not spread.
(B) prevent atmospheric interference.
(C) prevent interference by other lasers.
(D) ensure that people are not blinded by them.
h. For Gunn diodes, gallium arsenide is preferred to silicon because the former
(A) has a suitable empty energy band, which silicon does not have.
(B) has higher ion mobility.
(C) has a lower noise at the highest frequencies.
(D) is capable of handling higher power densities.
_______________________________________________________________
PART I
ans any 3 ques.. every ques. carries 14 marks.
_______________________________________________________________
Q.2
With the aid of energy bands, define the operation of a n-p-n junction transistor. How is the voltage amplification found with such a junction? (10)
The Hall coefficient of a p-type semiconductor is positive. discuss its significanc.
(7)
Q.3
explain briefly the velocity-electric field characteristics in an n-GaAs material. What is Gunn effect? Mention its various modes of operation (5+5+4)
Q.4
discuss the operation of a LED. explain briefly the internal quantum efficiency of an LED. Draw the structures of GaAs1-x Px red LED. Mention a few optical applications of LED. (5+4+3+2)
Q.5
explain the steps needed for an X-band GaAs MESFET low noise amplifier using S-parameter technique mentioning the implementation scheme for the input and output matching networks. Indicate also the steps needed for the prevention of high frequency oscillation effect.
(9+5)
Q.6 Write short notes on any 2 :-
(i) Capacitance voltage characteristics of a MOS capacitor.
(ii) Fabrication of a silicon IMPATT diode.
(iii) Gunn oscillator.
(7+7)
2
<
PART II
ans any 3 ques.. every ques. carries 14 marks.
_______________________________________________________________
Q.7
Compare the performance characteristics of a p-i-n photodiode & a p-n photodiode. Distinguish ranging from the internal & external quantum efficiency of a photodiode. (8+6)
Q.8 Describe the factors responsible for the losses of a solar cell.
(7)
Discuss the effect of concentrated sunlight on the efficiency versus band gap energy of a solar cell. (7)
Q.9 Discuss the issues connected with the biasing of a tunnel diode and their solution. Illustrate the discussion with a practical tunnel-diode circuit. (8)
Explain why it is possible to find amplification by using a device which exhibits negative resistance
(6)
Q.10 Briefly discuss the operation of a semiconductor laser, using a sketch showing the construction of this device.
(8)
What is the major application of semiconductor laser? How do GaAs and InGaAsP devices compare in this regard? (6)
Q.11
Write short notes on any 2 :
(i) Threshold control of MOSFET by Ion Implantation.
(ii) option of materials for LED.
(iii) Noise in Si and GaAs MESFETs. (7+7)
| Earning: Approval pending. |
