pn junction diode mcq for competitive exams

pn junction diode mcq

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pn junction is defined as :
When a p-type semiconductor is suitably joined to an n-type semiconductor, the contact surface so formed is called a p-n junction.
or
In other words,
If we join a piece of p-type material to the piece of N-type material such that the crystal structure remains continuous at the boundary, a p-n junction is formed.
Such a p-n junction makes a very useful device,which is called a semiconductor diode.

Furthermore, All the Semiconductor devices contain at least one p-n junction. So to understand the the working of various Semiconductor devices, it is essential for the readers to have a knowledge of p-n junction and its properties.This will help us to understand even those devices which have more than one p-n junction.

In actual practice, the p-n junction is not formed by just bringing a p-type semiconductor block near to an n-type semiconductor block as it looks.

Actually , p-n junctions are made by special techniques namely:
1.Growing
2.Alloying
3.Diffusion methods.

In which, growing and diffusion methods are the most common method of making a p-n junction .

First method,
1) Alloying :
An alloyed junction is made from an n-type slice of semiconductor by melting a pellet of trivalent indium placed on the slice. Step-wise, shown in figure,
This is done by heating the system to about 500 degree centigrade.
Then the Indium is absorbed into the Germanium or Silicon to produce a p-region.
Hence a p-n junction is formed.

pn junction diode mcq

pn junction diode mcq

pn junction diode mcq

Second method,
2) Diffusion :
However, diffusion process is also used in formation of a p-n junction. In this process , the semiconductor wafers of  one conductivity i.e. either p or n type are placed in a vessel that contains an oxide of the impurity to be added. The combination is passed slowly through a furnace with accurately known and controlled temperature of 800 degree centigrade to 1200 degree centigrade depending upon the type of junction desired .
At such a high temperature, a gas of impurity atom diffuses into the semiconductor material and forms a thin layer of opposite conductivity .

Thus , resulting in the formation of p-n junction .

pn junction diode mcq for competitive exam

In a PN junction with no external voltage, the electric field between acceptor and donor ions is called a

   A.Peak

   B.Barrier

   C.Threshold

   D.Path

The depletion layer of a PN junction diode has

   A.Only free mobile holes

   B.Only free mobile electrons

   C.Both free mobile holes as well as electrons

   D.Neither free mobile electrons nor holes

The depletion region of a PN junction is one that is depleted of

   A.Immobile charges

   B.Mobile charges

   C.Atoms

   D.None of the above

In an unbiased PN junction

   A.The junction current is due to minority carriers only

   B.The junction current at equilibrium is zero as equal but opposite carriers are crossing the junction

   C.The junction current reduces with rise in temperature

   D.The junction current at equilibrium is zero as charges do not cross the junction

The capacitance of a reverse biased PN junction

   A.Increases as reverse bias is increased

   B.Decreases as reverse bias is increased

   C.Increases as reverse bias is decreased

   D.Is insignificantly low

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