Profile
Settings
Refer your friends
Sign out
When the atoms of a selected element are so far apart, each atom shows allowable energy levels. Energy Bands in Solids in every particular element, the magnitude of the interaction of the neighbouring atom’s influence depends on the spacing and therefore the electron’s location inside the cluster of atoms. An energy band is a range of energy with several adjacent allowable energy levels, terribly close to each other.
Body
In step with the band theory of solids, in every crystalline solid, thanks to mutual interaction among valence electrons of neighbouring atoms, energy bands in solids are formed rather than sharp energy states.
The atoms are organised in a periodic crystal lattice in solids, and neighbouring atoms influence every atom. The proximity of the atoms results in the mixing of electrons from neighbouring atoms. Thanks to this, the amount of permissible energy levels increases.
Thus, within the case of a solid, there’ll be bands of energy levels instead of one energy level related to a single atom. A collection of such closely packed energy levels is named the associate energy band.
Every silicon atom has 14 electrons, 2 of which occupy the K shell, eight occupy the L shell, and 4 occupy the M shell. The electrons within the M shell are distributed as 2 electrons in the subshell 3s and a couple of electrons in the subshell 3p. This subshell 3p is partly stuffed because it can accommodate a total of six electrons. The inner filled levels are called core levels, so the electrons filling these levels are known as core electrons. The electrons within the outer level are called valence electrons. The partly filled outermost level is the valence level, and the vacant allowable levels are known as the conduction level of the solid. The energy of s or p level is of the order of eV. Therefore, the amount is very closely spaced. The primary orbit electrons form a band called 1st energy band. Similarly, second orbit electrons from the second energy band and then on.
Energy bands are of the subsequent three sorts
• Valence band is the energy band fashioned by a series of energy states of valence electrons present. Usually, the valence band is filled with electrons, and at 0K temperature, the electrons in this band don’t have enough energy to cross over to the conduction band.
• Conduction band is the energy level having energy significantly more than the valence band. If the electrons of the valence band gain energy then they will move to the conduction band. Electrons in the conduction band are ordinarily called free electrons.
• Impermissible band: The energy gap between the valence band and the conduction band of a solid is called the forbidden energy gap Eg or forbidden band. The extent of the prohibited energy gap depends on the nature of the substance.
In conductive solids, the valence band is filled, the conduction band is empty, and the energy gap between them is pretty small (for example, 0.1 eV).
A pure semiconductor, inside which no impurities of any kind have been mixed, is called an intrinsic semiconductor. Semiconducting material (Eg =0.72eV) and Si (Eg = 1.1 eV) are samples of intrinsic semiconductors. To prolong the conductivity of pure conductive material, it is doped with a controlled amount of appropriate impurities. Such a doped semiconductor is called an extrinsic semiconductor.
There are two types of semiconductor
· n-type semiconductor: when intrinsic semiconductors are doped by 5th group elements such as P, As, Sb and Bi then the semiconductor is called an n-type semiconductor. Such an impurity is called donor impurity due to every dopant atom providing one free electron. In an n-type semiconductor electrons are majority charge carriers and the holes are minority charge carriers.
· p-type semiconductor: when intrinsic semiconductors are doped by 3rd group elements such as B, Al, Gb and In then the semiconductor is called a p-type semiconductor. This impurity is called an acceptor impurity since each impurity atom wishes to accept a lepton from the crystal lattice. Thus, effectively each dopant atom provides a hole.
In a p-type semiconductor, i.e. The holes are majority chargers and electrons are minority charge carriers. The amount of free electrons in a semiconductor varies with temperature like T3/2.
Superconductors: Once a few metals have cooled down, their resistivity suddenly becomes zero below a specific essential temperature. These substances are called superconductors during this state, and associated degreed phenomena are called superconductivity. Mercury becomes a superconductor at 4.2 K, lead at 7.25 K and niobium (atomic number 41) at 9.2 K.
Conclusion
An electron occupies one of several allowed orbital patterns in an atom, each with its own set of energies. Though electrons in an atom will occupy solely specific energy levels, in a lattice, the opposite close atoms modify the precise energy levels of the electrons of an individual atom. As a result, energy levels change, and electrons can move at intervals, specific energy bands in solids. Many other higher energy empty crystal orbitals exist wherever the allowable energy levels jointly fall in bands. The associates in the exciting crystal can increase an electron from a valence orbital to a higher excited orbital. several allowed adjacent energy levels, terribly closely spaced
