# Electronic Devices and Circuits Questions and Answers – Transistor Construction

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Transistor Construction”.

1. Which gas is used to fill the chamber in the grown junction type transistor construction?
a) helium
b) boron
c) nitrogen
d) oxygen

Explanation: In the process of transistor construction, a crucible is placed in the chamber. This chamber consists of hydrogen or nitrogen. These gases help in the prevention of oxidation. It also contains purified Ge or Si at a temperature few degrees above its melting point.

2. In a grown junction type construction, the method used form a junction transistor is_________
a) alloy type diffusion
b) mesa type
c) speed variation method
d) fused junction type

Explanation: The grown junction may be formed by suddenly varying the rate of pulling the seed crystal from the melt. This method is based on the fact that proportion in which N and P type impurities crystallise i.e.., enter the grown crystal depends on the rate of pulling.

3. Which of the following methods take impurity variation method for transistor construction?
a) alloy type diffusion
b) grown junction type
c) epitaxial type
d) mesa type

Explanation: In impurity variation method, the impurity content of the semiconductor is altered in its type as well as the quantity. For example, in making NPN germanium grown junction transistor, a small type of N type impurity is added to molten germanium and the crystal growth is started.

4. Which of the following is true about grown junction type construction?
a) N type impurity is added to P type impurity
b) Boron helps in the prevention of oxidation
c) The seed is pulled to a large distance for a correct growth
d) Slow pulling leads to the formation of P type crystal

Explanation: This method is based on the fact that proportion in which N and P type impurities crystallise i.e.., enter the grown crystal depends on the rate of pulling. If the pulling rate is small, a P type crystal is grown. If the pulling rate is fast, an N type crystal is grown.

5. What is the melting point of indium in alloy type transistors?
a) 300°C
b) 200°C
c) 155°C
d) 100°C

Explanation: This is similar to soldering and PNP transistor is generally is made by this process. In this method, first of all N type germanium is obtained. The N type wafer and indium dots are placed in a furnace and heated to about 500°C.
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6. The non rectifying base contact is made from_________
a) welding a strip
b) germanium
c) indium
d) graphite

Explanation: Leads for emitter and collector are soldered to the dots making non rectifying contacts. Further, non rectifying base contact is usually made from a welding a strip or loop of gold plated wire to the base plate.

7. What is the thickness of wafer in the alloy type transistors?
a) 1-2m inch
b) 3-5m inch
c) 5-6m inch
d) 4-7m inch

Explanation: The wafer of crystal has a 3-5m inch thickness and 80m inch square. This is placed in a graphite jig with a dot of prepared indium. One dot of an indium is 3 times larger than the other.

8. The larger dot of the indium is used as_________
a) base
b) emitter
c) control pin
d) collector

Explanation: The wafer is placed in a graphite jig with a dot of prepared indium. One dot of an indium is 3 times larger than the other. Finally the larger dot is used as collector. The smaller dot is used as emitter.

9. The electrical properties of a transistor in alloy type construction is determined by_________
a) space between the junctions in the wafer
b) proportions of N and P type impurities
c) the pulling rate of crystal
d) uniformity of the crystal lattice

Explanation: Large area collector junction helps in collecting most of the holes emitted from the emitter ensuring that the collector current almost equals the emitter current. The spacing between two junctions inside germanium wafer is very small and determines the electrical properties.

10. The grown junction type transistors is generally used for_________
a) PNP transistors
b) NPN transistors
c) Both transistors
d) Depends on the material used

Explanation: Grown junction type transistors are manufactured through growing single large crystal which is slowly pulled from the melt in crystal growing furnace. This is generally used for NPN transistors.

Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.

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