SEMI CONDUCTOR THEORY&DIODES
The electrical properties of a material depends largely upon how tightly outer electrons with in the
atoms of that material are bound to the central nucleus. On the basis of this, materials can be
classified in to the following three groups.
Conductors
Insulators
Semi conductors
Material in which the electrons are loosely bound to the central nucleus is called conductor. In
conductor electrons are free to drift around the material at random from one atom to another.
Examples: Copper, Brass, Aluminium, Silver, etc.
Material in which the outer electrons are tightly bound to the nucleus is called insulator. There are
no free electrons in insulator to move around the material.
Examples: PVC, Rubber, Glass, Wood, etc.
Apart from conductors and insulators there are materials their conductivity lies in between the
conductivity of conductors and insulators and are called semi conductors.
Examples: Germanium, Silicon, Carbon, Selenium, etc...
ENERGY LEVEL
1. 3rd Energy level
2. 2nd Energy level
3. 1st Energy level
Nucleus
In an atom, the electrons revolve around the nucleus in different orbits. Each orbit has fixed amount
of energy associated with it and the electrons moving in a particular orbits posses the energy of that
orbit. The larger the orbit, the greater is its energy. Thus an electron in the outer orbit possesses
more energy than the electron in the inner orbit.
An electron orbiting very close to the nucleus in the first orbit is tightly bound to the nucleus and
possesses a small amount of energy. It would be difficult to knock out this electron. An electron
orbiting far from the nucleus would have a greater energy, and hence it could be knocked out of its
orbit easily.
3rd energy band
ENERGY BANDS
In a single isolated atom, the electrons in any orbit possesses a definite energy. However an atom in
solid is greatly influenced by the closely-Packed neighboring atoms. Since the electrons of the outer
sub shell are shared by more than one atom in the solid, the energy levels of outer shell electrons
are changed considerably. Because of this the electrons in the same shell have a range of energies
rather than a single energy. This range of energy is known as energy band.
The electrical properties of a material depends largely upon how tightly outer electrons with in the
atoms of that material are bound to the central nucleus. On the basis of this, materials can be
classified in to the following three groups.
Conductors
Insulators
Semi conductors
Material in which the electrons are loosely bound to the central nucleus is called conductor. In
conductor electrons are free to drift around the material at random from one atom to another.
Examples: Copper, Brass, Aluminium, Silver, etc.
Material in which the outer electrons are tightly bound to the nucleus is called insulator. There are
no free electrons in insulator to move around the material.
Examples: PVC, Rubber, Glass, Wood, etc.
Apart from conductors and insulators there are materials their conductivity lies in between the
conductivity of conductors and insulators and are called semi conductors.
Examples: Germanium, Silicon, Carbon, Selenium, etc...
ENERGY LEVEL
1. 3rd Energy level
2. 2nd Energy level
3. 1st Energy level
Nucleus
In an atom, the electrons revolve around the nucleus in different orbits. Each orbit has fixed amount
of energy associated with it and the electrons moving in a particular orbits posses the energy of that
orbit. The larger the orbit, the greater is its energy. Thus an electron in the outer orbit possesses
more energy than the electron in the inner orbit.
An electron orbiting very close to the nucleus in the first orbit is tightly bound to the nucleus and
possesses a small amount of energy. It would be difficult to knock out this electron. An electron
orbiting far from the nucleus would have a greater energy, and hence it could be knocked out of its
orbit easily.
3rd energy band
ENERGY BANDS
In a single isolated atom, the electrons in any orbit possesses a definite energy. However an atom in
solid is greatly influenced by the closely-Packed neighboring atoms. Since the electrons of the outer
sub shell are shared by more than one atom in the solid, the energy levels of outer shell electrons
are changed considerably. Because of this the electrons in the same shell have a range of energies
rather than a single energy. This range of energy is known as energy band.
