Carbon, silicon and germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by (Eg)C, (Eg)si and (Eg)Ge respectively. Which one of the following relationships is true in their case?
A
(Eg)C > (Eg)Si
B
(Eg)C < (Eg)Si
C
(Eg)C = (Eg)Si
D
(Eg)C < (Eg)Ge.
Explanation
Band gap of carbon is 5.5 eV while that of
silicon is 1.1 eV
$$ \therefore $$ (Eg)C $$>$$ (Eg)Si
2
MCQ (Single Correct Answer)
AIPMT 2005
Zener diode is used for
A
amplification
B
rectification
C
stabilisation
D
producing oscillations in an oscillator.
Explanation
Zener diode is used for stabilisation while
p-n junction diode is used for rectification.
3
MCQ (Single Correct Answer)
AIPMT 2005
Application of a forward bias to a p-n junction
A
widens the depletion zone
B
increases the potential difference across the depletion zone
C
increases the number of donors on the n side
D
decreases the electric field in the depletion zone.
Explanation
Number of donors is more because electrons
from –ve terminal of the cell pushes (enters)
the n side and decreases the number of
uncompensated pentavalent ion due to which
potential barrier is reduced. The neutralised
pentavalent atom are again in position to
donate electrons.
4
MCQ (Single Correct Answer)
AIPMT 2005
Choose the only false statement from the following.
A
In conductors the valence and conduction bands overlap.
B
Substances with energy gap of the order of 10 eV are insulators.
C
The resistivity of a semiconductor increases with increase in temperature.
D
The conductivity of a semiconductor increases with increase in temperature.
Explanation
Option (a) is correct as in conductor conduction
and valance band overlap and the conduction band
is partially filled
Option (b) is correct as insulators have energy gap
of 5 - 10 eV.
Option (c) is incorrect as resistivity decreases with
increase in temperature.
Option (d) is correct as with increase in temperature,
more and more electrons jump to conduction band,
hence conductivity increases.
Questions Asked from Semiconductor Electronics
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