About Doping in semiconductors

Doping :

         Doping is the process of adding impurities to intrinsic semiconductor materials to change electrical properties like carrier concentration. Doped semiconductor material is also called as extrinsic semiconductor. Depends on conductivity requirements doping levels may be changed.  A semiconductor doped in high levels that it acts more like a conductor than a semiconductor is referred to as degenerate.

Effects after doping :

The most important factor that doping directly affects is the material's carrier concentration. In an intrinsic semiconductor under thermal equilibrium, the concentration of electrons and holes is equivalent. That is,

n = p = n_i

If we have a non-intrinsic semiconductor in thermal equilibrium the relation becomes (for low doping):

n_0  * p_0 = n_i^2 


where n_0 is the concentration of conducting electrons, p_0 is the electron hole concentration, and n_i is the material's intrinsic carrier concentration. Intrinsic carrier concentration varies between materials and is dependent on temperature.

          An increase in doping concentration affords an increase in conductivity due to the higher concentration of carriers available for conduction. Degenerate (very highly doped) semiconductors have conductivity levels comparable to metals and are often used in modern integrated circuits as a replacement for metal. Often superscript plus and minus symbols are used to denote relative doping concentration in semiconductors. For example, n+ denotes an n-type semiconductor with a high, often degenerate, doping concentration. Similarly, p− would indicate a very lightly doped p-type material. 

            The Group IV semiconductors such as diamond, silicon, germanium, silicon carbide, and silicon germanium, the most common dopants are acceptors from Group III or donors from Group V elements. Boron, arsenic, phosphorus, and occasionally gallium are used to dope silicon. 
               By doping pure silicon with Group V elements such as phosphorus, extra valence electrons are added that become unbonded from individual atoms and allow the compound to be an electrically conductive n-type semiconductor. 

                By doping with Group III elements, which are missing the fourth valence electron, creates "broken bonds" (holes) in the silicon lattice that are free to move. The result is an electrically conductive p-type semiconductor.

  In this context, a Group V element is said to behave as an electron donor, and a group III element as an acceptor.

After Doping

In Single word : Adding impurities 

                

About Semiconductors & Types

A semiconductor material has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Semiconductors are the foundation of modern electronics. Semiconducting materials exist in two types - elemental materials and compound materials.
      Generally we have different types of semiconductors based on properties in that
                         1. intrinsic semiconductor
                         2. Extrinsic semiconductor

Intrinsic semiconductors :
             An intrinsic semiconductor material is also called as undoped semiconductor or i-type semiconductor, is chemically very pure and possesses poor conductivity. It has equal numbers of negative carriers (electrons) and positive carriers (holes). A silicon crystal is different from an insulator because at any temperature above absolute zero temperature, there is a finite probability that an electron in the lattice will be knocked loose from its position, leaving behind an electron deficiency called a "hole".
                 by we applying external energy (voltage,temperature) both the electrons and the holes can contribute small current flow.

In Single Word : pure semiconductor

Extrinsic Semiconductor :

             Where as an extrinsic semiconductor is an improved intrinsic semiconductor with a small amount of impurities added by a process, known as doping, which alters the electrical properties of the semiconductor and improves its conductivity. Introducing impurities into the semiconductor materials (doping process) can control their conductivity.

                                 

            

About solid state materials

Solid-state materials can be classified into three groups:
                 1. insulators
                 2. semi conductors
                 3. conductors

Insulators :
Insulators are those materials that don't conduct electricity under normal conditions. For instance: air is an insulator. You don't get electrocuted when approaching a plug point since air is an insulator. 
. The outer most orbit of an atom can be divided into various sub orbitals or bands. As you can see I have divided into three colors. The lower most band is called a valence band. The electrons in this band determine the valency of the atom. The upper most band is called the conduction band. In this band, the electron is farthest from the positively charged nucleus and is capable of easily escaping out of the atom and thus enabling the material / atom to conduct electricity.

Single Word : zero conductivity

semiconductors :
Semiconductors are materials that behave like both conductors and insulators. In certain condition a semiconductor acts like a conductor. For example charcoal and graphite which are allotrope of Carbon act as conductor. Whereas diamond which has a different crystal structure act as an insulator. The conductivity of semiconductors can be increased by adding certain impurities to them this is called doping. The conductivity may increase by pumping energy into semiconductor crystal in the form of heat or light.

Single Word : conducts by external influence (energy,temperature) 

Conductors :
Conductors are substances that easily let electrical charge pass through them with relatively very-less resistance. Almost all metals are conductors. When ever you cut an electric wire, you can see copper or some other metal at its core. Its because these metals can easily conduct electricity. 
 there is no forbidden energy gap. The valence and conduction band are overlapping each other. Hence its extremely easy for electrons to move from valence to conduction band. Hence conductors easily conduct electricity without much loss of energy. They conduct electricity under normal conditions.

Single word :  External influence is not required to conducts.

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