SEMICONDUCTOR n-type


   when a small amount of pentavalent impurities is added to a pure semiconductor, it is known as an n-type semiconductor. The addition of pentavalent impurities produces a large number of free electrons in the semiconductor crystal, from the bonding diagram.
 Since arsenic is a pentavalent element, the four valence electrons of germanium form a covalent bond with the arsenic atom and the electrons of the fifth valence are left free producing n-type conductors.

 SEMICONDUCTOR p-type

   When a small amount of trivalent impurities is added to a pure semiconductor, it is called p-type semiconductor. Such impurities that produce the p-type Semiconductor are known as acceptor impurities because the holes created can accept the electrons. The formation of the p-type semiconductor can be explained with the help of the connection diagram mentioned above. 
When a small amount of trivalent impurities such as gallium is added to the pure germanium crystal, there is a large number of holes in the crystal. Germanium is a tetravalent element that has four valence electrons, while gallium is a trivalent element that has three valence electrons. The three valence electrons of germanium are covalently linked with the three valence electrons of gallium and the fourth valence electrons are left free. This lost electron is called a hole. For each gallium atom, a created hole was added. A small amount of gallium provides millions of holes. 

CHARGE ON  n-type  and  p-type SEMICONDUCTOR

   In general the p-type and n-type Semiconductors are electrically neutral. In a p-type semiconductor, there is an excess of holes, whereas in n-type Semiconductors there is an excess of free electrons. The excess in p-type as well n-type depends on the type of impurity added to the type of semiconductors and the excess is not due to the Semiconductors of its own.

MAJORITY AND MINORITY CARRIERS

  In a p-type Semiconductor, the majority carriers are the holes. In an n-type semiconductor, the majority carriers are the electrons. It does not mean that the p-type Semiconductors has only holes but it has electrons also. The same in case of n-type Semiconductors also. To conclude the condition in a semiconductor is both by electrons and holes.

Pn-JUNCTION


   When a p-type semiconductor is combined with an n-type semiconductor, the resulting PN junction has unique characteristics. The PN junction is also known as Semiconductor or crystal diode, the outstanding property of the crystal diode to conduct the current in one direction only. Only when it is polarized forward, in direct polarization conditions, external power supply voltage is given to the diode. When the positive supply of the external supply is given to the anode, the negative terminal of the external supply is applied to the cathode. it is said that the diode is predisposed. In a direct polarization condition, the diode has low resistance and high conduction. In reverse bias conditions, the PN junction has high resistance and low conduction. The particular property of the diode to conduct the current in one direction is used to use it as a rectifier. A rectifier is a device that converts the available alternating current into the required current.


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