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Physic - Semi Conductor

Questions

1. When a p-n junction is under reverse bias mode, the width of the depletion region will be increased. Which of the following statements is true?


A. The applied voltage moves the electrons from n-type region to p-type region.

B. The applied voltage moves the holes from p-type region to n-type region.

C. The applied voltage drives the electrons towards n-type region.

D. The applied voltage drives the holes towards n-type region.


Explanation:

Under reverse bias mode, the electrons in the n-region are pulled away from the depletion region, leaving more immobile positive ions in the region. In other words, the electrons are driven towards the n-region.

Answer is C


2. Which statement about conduction of electricity in semiconductors is correct?


A. The presence of impurities in a semiconductor is used to decrease its resistance.

B. In a semiconductor, there is a large energy gap between the conduction and valence bands.

C. At low temperatures, free electrons are found both in the conduction band and in the valence band.

D. In an intrinsic semiconductor, electrons travel in the same direction as the holes.


Explanation:

The presence of impurities in a semiconductor increases the conductivity, hence decreases the resistance.

Answer is A


3. Which of the following statements about semiconductors is true?


A. The empty energy bands overlap with the bands containing electrons so that current can be conducted.

B. When an external electric field is applied, both conduction electrons and holes move in the same direction to contribute to current flow.

C. At temperatures above 0K, some free electrons in the energy gap are free to conduct electricity.

D. As temperature increases, the resistivity of the material drops.


Explaination:

For option A: The valence and conduction bands overlap only for conductors.

For option B: When an electric field is applied, electrons and holes should move in opposite directions.

For option C: There should not be any free electrons in the energy gap.

For option D: As temperature rises, resistivity drops.

Answer is D


4. In order to produce a p-n type silicon semi-conductor, how many valence electrons does each of the doping atoms need to have?


A. 3

B. 4

C. 5

D. 6


Explaination:

Dopants with 3 valence electrons create a p-type semiconductor because they donate an excess of positive charge carriers. The 3 valence electrons form covalent bonds with semiconductor atoms, leaving a hole which can carry current in the presence of an electric field.

Answer is A


5. Due to bombardment by light, an electron-hole pair is generated in the depletion layer of a p-n junction. What is the subsequent motion of the electron and the hole?


A. The electron drifts towards the n side while the hole drifts towards the p side.

B. The electron diffuses towards the p side while the hole diffuses towards the n side.

C. The electron and hole move towards the nearest donor ion and acceptor ion respectively.

D. The electron and hole cannot move because they are in the depletion layer.


Explaination:

Electrons should drift towards the n side while holes drift towards the p side.

Answer is A


6. Which of these is true for a forward biased diode


A. No current passes true

B. Wider deflection layer

C. High current

D. Low current


Explaination:

For a forward biased diode, current passing through it is high because it flows in a straight direction

Answer is C


7. A Transistor is made up of ______ diodes

A. 1

B. 2

C. 3

D. 4


Explaination:

When you join two diodes together N-type and P-type, I Transistor is formed.

Answer is B 


8. Which is not a type of diode

A. Zener diode

B. LED

C. Laser diode

D. Gamany diode


Explaination:

Gamany is not a type of diode

Answer is D


9. The impurity in a P-type semi-conductor is

A. Boron

B. Helium

C. Nitrogen

D. Nacl 


Explaination:

Impurities in a P-type semi-conductor are all group 3 element

Answer is A


10. The impurity in a P-type semi-conductor is


A. Aluminum

B. Helium

C. Phosphorus

D. Hcl


Explaination:

Impurities in a N-type semi-conductor are all group 5 element


Answer is C

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