As per Niel Bohr’s hypothesis of nuclear construction, all molecules have discrete energy levels around their focal core (erring on this in the article “Nuclear Energy Levels”). Presently consider the case wherein at least two such molecules are put near one another. For this situation, the design of their discrete energy levels changes to an energy band structure. That is, instead of discrete energy levels, one can find discrete energy groups. The justification for the development of such energy groups in gems is the common communication between the molecules which is the aftereffect of the activity of electromagnetic powers between them.
Figure 1 shows a run of the mill plan of such energy groups. Here energy band 1 can be considered as energy level E1 of segregated molecule and energy band 2 as level E2, etc.
This is likeness being said that the electrons closer to the core of the cooperating iotas comprise energy band 1 while those in their comparing external circles bring about higher energy groups.
Actually, every one of these groups is numerous energy levels which are firmly separated.
From the figure, it is obvious that the quantity of energy levels which show up in a specific energy band increments with the expansion in the energy band considered for example the third energy band is more extensive than the subsequent which is anyway seen to be more extensive when contrasted and the first. Then, the space between every one of these groups is called illegal band or band hole (Figure 1). Further, every one of the electrons present inside the precious stone are compelled to be available in any of the energy groups. This inturn implies that the electrons can’t be found in the energy band hole locale.
Types of Energy Bands:
Energy bands in crystals can be of different types. Some of them will be completely empty which is why they are called empty energy bands while others will be completely filled and thus named as flooded energy bands. In general, filled energy bands will be the lowest energy levels that are close to the nucleus of an atom and have no free electrons, meaning they cannot conduct. There is another set of energy bands which can be a combination of empty and filled energy bands called mixed energy bands.
Yet in the field of electronics one is particularly interested in conduction mechanisms. As a result, here, two energy bands gain extreme importance.
Valence Band:
This energy band consists of valence electrons (the electrons in the outermost orbital of an atom) and can be completely or partially filled. At room temperature, this is the highest energy band that contains electrons.
Conduction Band:
The lowest energy band, which is normally empty of electrons at room temperature, is called the conduction band. This energy band consists of electrons that are free from the attractive force of the atomic nucleus.
Generally, the valence band is a lower energy band than the conduction band and thus is found below the conduction band in the energy band diagram (Figure 2). Electrons in the valence band are loosely bound to the atom’s nucleus and jump into the conduction band when the material is excited (say, thermally).
Importance of Energy Bands:
It is notable that conduction through materials is simply because of free electrons in them. This reality can be re-expressed as far as energy band hypothesis as “electrons in the conduction band are the ones in particular that add to the conduction component”. Therefore, one can characterize materials into various classes by taking a gander at their energy band graphs.
For instance, say, the energy band chart shows extensive covering between the valence and conduction groups (Figure 3a), then, at that point, this implies that the material has a wealth of free electrons, which It tends to be viewed as a valid justification. Channel of power for example metal.
Then again on the off chance that we have an energy band chart in which there is an enormous hole between the valence and the conduction groups (Figure 3b), this implies that one requirements to furnish the material with huge measure of energy to get the filled conduction band. Now and again, this might be extreme or in some cases even basically unimaginable. This would pass on the conduction band bereft of electrons because of which the material will neglect to direct. Hence, these sort of materials would be covers.
Presently, let us say that we have a material which shows a slight partition between the valence and the conduction groups as shown by Figure 3c. For this situation, one can make the electrons in the valence band possess the conduction band just barely of energy. This intends that albeit such materials are normally covers, they can be switched over completely to go about as guides by intriguing them remotely. Thus these materials will be called.
