MERU UNIVERSITY OF SCIENCE AND TECHNOLOGY
P.O. Box 972-60200 – Meru-Kenya
Tel: +254(0) 799 529 958, +254(0) 799 529 959, + 254 (0) 712 524 293,
Website: info@must.ac.ke Email: info@must.ac.ke
University Examinations 2018/2019
FIRST YEAR SECOND SEMESTER EXAMINATION FOR THE DEGREE OF
BACHELOR OF TECHNOLOGY IN ELECTRICAL AND ELECTRONIC ENGINEERING
AND
SECOND YEAR SECOND SEMESTER BACHELOR OF TECHNOLOGY IN
ELECTRICAL AND ELECTRONICS ENGINEERING
EET 3153: PHYSICAL ELECTRONICS
DATE: MAY 2019
TIME: 2 HOURS
INSTRUCTIONS: Answer question one and any other two questions
QUESTION ONE (30 MARKS)
a) Define the following terms
i.
Laser
ii.
Lasing
iii.
Luminescence
iv.
External quantum efficiency
v.
Electroluminescence
(5 marks)
b) i. A semiconductor laser has a length of 250 µm . Injection of current into the laser
create a gain coefficient of 250cm-1 in the gain region. The optical confinement factor
is 0.3, the gain region has imperfections that contribute a distributed optical loss
α =40cm-1. The front mirror of the laser is uncoated what must be the reflectance of
the back surface to achieve lasing?
(4 marks)
ii.With the aid of diagrams, explain the following components and state where they are
used in electronics
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I.
Zene- diode
II.
Varactor chode
(6 marks)
c) i. State the meaning of the term “doping” as applied to semiconductor materials
(3 marks)
ii.Differentiate clearly between “intrinsic conduction” and “extrinsic conduction” in
semiconductor materials
(4 marks)
iii.An earth satellite has on board 12-v battery which supplies a continuous current of
0.5A. Solar cells are used to keep the battery charged. The solar cells are
illuminated by the sun for 12hours in every 24hours. If during exposure, each cell
gives 0.5v at 5MA, determine the number of cells required
(5 marks)
iv. Differentiate with diagrams a forward biased and reversed biased diode (3 marks)
QUESTION TWO (15 MARKS)
a) i. With the aid of a diagram describe a P-N function diode and clearly state when the
potential barrier forms at the function
(9 marks)
ii. With the aid of diagrams, discuss the three main process for laser action (6 marks)
QUESTION THREE (15 MARKS)
a) i. The radiative and nonradiative recombination lifetimes of the minority carriers in the
active region of a LED are 60ns and 100ns. Determine the total carrier recombination
lifetime and the power internally generated within the device when the peak emission
wavelength is 870nm at a driving current of 40MA
(6 marks)
ii. Explain the difference between insulators, semiconductors and conductor materials
using the following concept
a. Electro theory concept
(2 marks)
b. Energy bad concept
(2 marks)
iii. Based on Fresnel loss show that the light that escapes through the boundary to the
air is given by
4n
(n + 1)2
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(5 marks)
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QUESTION FOUR (15 MARKS)
a) i. An 8.2V zener diode (8.2V at 250C) has a positive temperature coefficient of 0.05%
%C. What is the zener voltage at 600C?
(2 marks)
ii. Explain how population inversion is achieved using suitable illustration (4 marks)
iii. Using appropriate energy diagrams. Explain the two types of band gap
semiconcuctors
(9 marks)
QUESTION FIVE (15 MARKS)
a) i. Describe three losses that occur in a LED
(3 marks)
ii. Describe conditions for LASING
(5 marks)
iii. Discuss with aid of diagrams the characteristics of a tunnel diode
(7 marks)
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