electrical properties of semiconductors
Uploaded by pavan on Jul 01, 2014
ELECTRICAL PROPERTIES OF SEMICONDUCTORS
It is a known fact that electrons revolve round the nucleus in definite circular orbits under the influence of short range attractive forces called nuclear forces. If the potentiality of electron is strong enough to overcome this force of attraction we can designate them as conductors, on the other hand if the energy of electron is least to overcome the nuclear short range forces such materials are called as insulators or in simple words we can say that materials which reveal intermediate behaviour in between conductors and insulators are termed as semiconductors. At Ok semiconductors behave themselves as insulators, because it is general pedagogy that all electrons at Ok will be localised in the valence band. As a result of this electrons cannot jump from valence band to conduction band because they are tightly bounded themselves, even after the application of higher temperatures only few electrons will try to jump to conduction band. So on the whole some of the insulators at OK will behave as a conductor at room temperature.
The band formed by valence electrons is valence band it is always fulfilled but can never be empty, on the other hand band formed by conduction electrons will serve as conduction band. For an electron to behave as an conductor there should be an unfilled electron in its configuration, the conduction band may be partially filled or empty. Since energy band is nothing but the packet of energy levels, they may be degenerative or non degenerative energy levels depending on the nature of atom. If the atom is in isolated form the energy levels are non degenerative and degenerative in the sense if it is unisolated form. The gap between conduction band and valence band is called forbidden band where the electron cannot stay less than a nanosecond of time. The phenomenon of semiconductors can be best understood with the help of quantam mechanics which specifies the motion of microscopic particles electrons by assuming that the electron has got particle nature and wave nature as proposed by debroglie.
Semiconductor is nothing but a crystal where constituent particles like atoms or molecules are arrayed in...