Introduction
In an isolated atom, electrons are present in energy levels but in solid atoms are not isolated there is the interaction among each other due to this energy level split into different energy levels. The quantity of these different energy levels depends on the number of interacting atoms. The formation of the energy band is due to the splitting of sharp and closely compact energy levels. This is a decrease in nature. The order of energy levels in a band is 1030. The range of energy possessed by electrons in a solid is known as the energy band. Or it can also be defined as in gaseous substances their molecules are not closely arranged and in liquid also their molecules are not that much closer to each other. Whereas in the case of solid they have the strongest intermolecular force due to this their atom or molecule tends to move into orbitals of neighbouring atoms. Hence when they come together their electronic orbitals overlap. They have several bands of different energy levels, which are formed by the intermixing of atoms in solids and this set of energy levels is known as energy bands.
Band Theory
We have understood that materials can be classified into conductors, insulators. and semiconductors. We can make the study of their properties easier by plotting out their electron energies. It has been observed that energy states in these materials lead to the formation of energy bands, unlike the phenomenon that is observed in free atoms. In a free atom, each atom has a distinct energy level.
A major determinant of the properties of these materials will be the position of the electrons. If the electrons are inside the conductivity band, we can proceed to study the properties of the materials. In insulators, the electrons inside the valence band are separated from the conduction band by the forbidden energy gap. In contrast to this, the valence band overlaps the conduction band in metals. In semiconductors, this forbidden energy gap is so small that any thermal or other excitations can bridge the gap.
It has been noticed that the presence of a doping material in semiconductors can increase their conduction capacity by leaps and bounds. An important factor that is taken into consideration as part of the band theory is the Fermi level, which demonstrates the highest accessible electron energy levels at lower temperatures. The position of the Fermi level with respect to the conductivity band is a crucial parameter.
Different Types of Energy Bands
Valence Band: Valence electrons are those electrons that are present in the outermost shell. They have different energy levels and form an energy band known as the valence band. They occupy a maximum amount of energy.
Conduction Band: As outermost electrons are not tightly held to the nucleus due to which sometimes they leave the outermost orbit at room temperature and become free electrons. These free electrons tend to conduct current in conductors and this is the reason they are known as conduction electrons. Therefore the conduction band is that band that contains conduction electrons and has the lowest occupied energy. A wide bandgap tells us about different conditions required to energize valence electrons to conduction bands. In the case of metals both valence band and conduction band overlap each other, electrons can promptly bounce between the two groups which show the material is profoundly conductive.
Forbidden Energy Gap: The gap present between the conduction band and valence band is known as the forbidden energy gap. If the forbidden energy gap is more, then the valence band electrons are tightly bound or attached to the nucleus.
Conduction Band in Semiconductor and Metals
In metals, the conduction electrons are compared to the valence electrons of given constituent molecules. Whereas in semiconductors at low temperatures, the conduction band has no electrons. Origination of conduction electrons is due to thermal excitation from a lower energy band or impurity atoms in the crystal.
What is a Conduction Band?
Band of electron orbitals that electrons can jump from a lower energy level to a high energy level when they get excited and this band is known as the conduction band. When electrons are in an excited state, they have enough energy to move freely in the material. Due to this flow of electrons, there is a flow of electric current. There is an energy gap between the highest occupied energy state of the valence band and the least energy state of the conduction band and this gap is known as bandgap and is used for the electrical conductivity of the material. This vast gap symbolizes that a large amount of energy is required to excite electrons to the conduction band. After this again valence band and conduction band coverup as they do in the case of metals, as electrons can jump to and fro to both groups which indicate the material is highly conductive.
Conductivity
We have already defined resistivity in the chapter on Current Electricity. The reciprocal of resistivity is conductivity and it comes into play here. Conductivity is a factor used to measure the flow of electrons in any given material. Copper has a very high conductivity of 5.95 x 107 W-1m-1, thereby allowing electricity to flow more freely than aluminium. Aluminium has a slightly lower conductivity of 3.77 x 107 W-1m-1 when compared to copper.
Difference Between the Valence Band and Conduction Band
Conduction Band Valence Band :
The energy bands are of higher energy levels. This band is formed by a series of energy levels containing valence electrons
In this band, electrons are partially filled. Here electrons are filled. Here is the empty band of minimum energy. Here is an empty band of maximum energy. Their electrons can gain energy from external electric fields. Here electrons cannot gain energy from external electric fields. The flow of current is due to the presence of such electrons. Valence bonds occupy the highest energy level at 00 K and this is called the Fermi level.
FAQs on Conduction Band
1. Explain the term conduction band?
Conduction Band: As outermost electrons are not tightly held to the nucleus due to which sometimes they leave the outermost orbit at room temperature and become free electrons. These free electrons tend to conduct current in conductors and this is the reason they are known as conduction electrons. Therefore the conduction band is that band that contains conduction electrons and has the lowest occupied energy. A wide bandgap tells us about different conditions required to energize valence electrons to conduction bands. In the case of metals both valence band and conduction band overlap each other, electrons can promptly bounce between the two groups which show the material is profoundly conductive.
2. Explain the term band theory in solid?
In an isolated atom electrons are present in energy levels but in solid atoms are not isolated there is the interaction among each other due to this energy level split into different energy levels. The quantity of these different energy levels depends on the number of interacting atoms. The formation of the energy band is due to the splitting of sharp and closely compact energy levels. This is a decrease in nature. The order of energy levels in a band is 10³⁰. The range of energy possessed by electrons in a solid is known as the energy band. Or it can also be defined as, in gaseous substances, their molecules are not closely arranged and in liquid also their molecules are not that much closer to each other. Whereas in the case of solid they have the strongest intermolecular force due to this their atom or molecule tends to move into orbitals of neighbouring atoms. Hence when they come together their electronic orbitals overlap. They have several bands of different energy levels, which are formed by the intermixing of atoms in solids and this set of energy levels is known as energy bands.
3. What is the forbidden energy gap?
In the chapter solid state, we study the forbidden energy band gap which is also sometimes simply called an energy gap. It is the energy range in a solid where no electronic states or electrons can exist. If we were to plot graphs of solids, the band gap generally would refer to the energy difference between the two bands, namely the valence band and the bottom of the conduction band. This energy difference is most commonly measured in electron volts or eV. This gap is seen only in insulators and semiconductors as the conduction band and the valence band overlap in conductors. This forbidden energy gap is demonstrative of the energy required to promote a valence electron bound to an atom to become a conduction electron. Such conduction electrons are free to move within the lattice of the structure of the material. They further serve as carriers to conduct electric current.
4. What is solid-state in Physics?
Before microscopic methods of detection were developed, the physical properties of solids intrigued scientists for a long time. A branch of physics named solid-state physics soon developed to satisfy this innate curiosity to know more about the materials and compounds that surrounded us. Thus, it is rightly said that solid-state physics refers to that branch of physics that deals with the study of solid materials. A wide assortment of techniques is used to determine the properties and structure of these solids. These techniques include modern quantum mechanics, electromagnetism, metallurgy, and crystallography. The foundation of the Division of Solid State Physics (DSSP) within the American Physical Society was the turning point that birthed this branch of physics. A few decades later, the DSSP has established itself as the most significant division of the American Physical Society. To know more, check out the official website of Vedantu or download the app.
5. How are semiconductors different from conductors?
Semiconductors are different from conductors as they have a conductivity range that lies between conductors and insulators. Semiconductors can be compounds formed by a combination of elements or pure elements themselves. Examples include gallium arsenide, germanium, and silicon. Solid-state physics explains the various approaches, theories, properties and mathematical calculations governing semiconductors. The concept of holes and electron carriers in semiconductors is important and needs to be studied carefully. The mobility of electrons is higher than that of the holes in such materials.