Conductors, Insulators and Semi-Conductors

Conductors, Insulators and Semi-Conductors

Electrical properties of various materials are determined by the number of electrons in the outer ring of their atoms.

Conductors




Materials with 1-3 electrons in the atoms outer ring make it easy for electrons to move from atom to atom. Remember that the definition of current flow is the movement of tree electrons from one atom to another. The electrons in the outer ring of these conductors are loosely held and even a low EMF will cause the flow of free electrons.
Many metals are good conductors, especially gold, silver, copper, and aluminum. But not all conductors have the same amount of resistance to the flow of free electrons.

Insulators







Materials with 5-8 electrons in their outer ring have those electrons bound tightly. These materials are insulators (Poor conductors).

The electrons in the outer rings resist movement, the atoms don't give up the electrons easily or accept tree electrons easily.

This effectively stops the flow of free electrons and thus any electrical current.
Rubber, glass, and certain plastics are examples of good insulators.

Insulators are used in circuits to insure that the flow of electrons stays in the conductor and can be directed to the proper place in the system.

Semi-Conductors







Materials with exactly 4 electrons in the atoms outer ring are neither conductors nor insulators.

The 4 electrons in the outer ring cause special electrical properties which give them the name "Semi-Conductor".

Materials such as Germanium and Silicone are are two widely used semi-conductors.

Semi-Conductor Doping







When semi-conductors are in the form of a crystal, the four electrons of the outer ring are shared with a neighboring atom.

This makes the crystal form of these materials an excellent insulator because there are no free electrons to carry a current flow.

Other elements (Impurities) can be added to change the crystalline structure of the Germanium and Silicone.

This is called Doping of the semi-conductors.
Doping creates free electrons or holes enabling the semi-conductor to carry current.

N-Type Material







If the semi-conductor is doped with an element having 5 electrons in its outer ring there will not be enough space in the outer ring for the 9th electron (4 electrons in the semi-conductor and 5 in the impurity).

This type of doped material is called negative or N-material, because it already has excess electrons and will repel additional negative charges.

P-Type Material







If the semi-conductor is doped with an element having 3 electrons in its outer ring some of the atoms will only have 7 electrons in the outer ring. There will be a hole in some of the outer rings.
This type of doped material is called positive or P-material because it will attract free electrons

Junctions

Doping Germanium and Silicone cause them to behave in unusual but predictable ways when exposed to voltage, depending on which charge of the voltage is connected to which type of material (P or N).

The line along which joined P and N material meet is called the Junction. A simple component consisting of P-material and N-material joined at a junction is called a diode. The application of voltage to the two doped semiconductor materials is called biasing.

A more complex material containing two PN junctions is called a Transistor.