A rise in temperature increases the conductivity of a semiconductor because more electrons will have enough energy to move into the conduction band. Ordinarily, gases are poor conductors due to the space between atoms. However, in some circumstances — such as when it contains a large number of ions — gasses can be fair conductors and act as semiconductors. An insulator prevents the flow of energy between two objects.
For example, insulators may prevent the flow of electric, heat or sound. Thermal insulators, reduce the transfer of heat between two objects of differing temperatures. Thermal insulators do this by reflecting thermal energy.
The insulative capacity of a material is the inverse of thermal conductivity k and therefore those materials with low thermal conductivity will have high insulating capability or resistance value.
A substance that does not conduct electricity is called a dielectric material. These substances can be polarised by an applied electric field so electric charges do not flow through them as they would through a conductor. Therefore, the internal electrical field reduces the overall field within the dielectric.
In insulators, there are larger gaps between the conduction and valence bands. The electrons cannot move into the conduction band and this means the material cannot conduct. Semiconductors are all around us but perhaps are less obvious than conductors or insulators.
Semiconductors use include:. Insulators have a wide range of applications from everyday use through to specialist and high-tech industrial applications. Their atoms are arranged in a 3D pattern. When considering a silicon crystal, each silicon atom is surrounded by four other silicon atoms. These atoms have covalent chemical bonds between them. The energy gap between the conduction band and valence band of a silicon crystal is called the band gap.
For semiconductors, the band gap is usually between 0. Superconductors are materials that have electrical conductivity value above the conductivity value of a conductor. It can be a chemical element or a compound that dramatically loses its electrical resistance when cooled below a certain temperature. Therefore, a superconductor allows the flow of electrical energy without any energy loss. This energy flow is called supercurrent. However, it is very difficult to produce superconductors.
The temperature at which these materials lose their electrical resistance is called the critical temperature or Tc. All the materials we know cannot turn into superconductors below this temperature. Materials having a Tc of their own can turn into superconductors. The valence band and conduction band are separated by the energy band gap of 6eV. Thus electrons do not move from valence band to conduction band under the influence of any thermal agitation. The bond between the atoms is the covalent bond and ionic bond.
The electron holds the atom very tightly and does not permit electron flow. The temperature coefficient of resistance is negative for insulators. Semiconductors are the material whose conductivity lies between insulators and conductors. At absolute zero temperature, the semiconductor behaves like an insulator whereas by providing thermal agitation, the charge carriers start moving from valence band to conduction band.
The valence band and conduction band are separated by the energy band gap of nearly 1eV. The bonding between atoms is the covalent bond. The semiconductor can be classified as an intrinsic and extrinsic semiconductor. The intrinsic semiconductor is the pure form of the semiconductor.
The process of adding impurities to the intrinsic semiconductor is called doping. After doping intrinsic semiconductor behaves as an extrinsic semiconductor, and becomes good conductor of electricity. The current flow because of the movement of electrons and holes. The holes flow opposite to the direction of electrons flow. Semiconductors are having a negative temperature coefficient of resistance. Hence the resistivity decreases with the increase of temperature which in turn increases the conductivity.
The crucial difference between conductor, insulator and semiconductor is that the conductivity of semiconductor lies between the conductivity of insulator and conductor. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Some other differences between conductor, insulator and semiconductor are explained below:.
Key Differences Between Conductor, Insulator and Semiconductor In conductors, the valence band and conduction band overlapped each other thus under the influence of electric field the charge carriers easily move to the conduction band, and this results into easily flow of current. In Insulators the energy gap is very high, there is no flow of electric charge, whereas in the semiconductor the valence band and the conduction band is separated by very less eV thus charge carrier flow is very less, and current will be very less.
The flow of charge carriers decides the material, if the charge carriers flow easily under the influence of electric field, then they are called as a conductor, the material in which charge carriers do not flow easily then they are called as insulators while the material whose conductivity lies between conductor and insulators are called as a semiconductor.
In the case of conductors, resistance depends on the temperature thus resistivity increases with temperature hence having a positive temperature coefficient of the resistance, which is inversely proportional to the conductivity thus conductivity decreases, while insulators are having negative temperature coefficient of resistance similar to insulator semiconductor is also having negative temperature coefficient of resistance hence increases conductivity.
In the conductor, current flows because of negatively charged carriers called as electrons. In Insulator there is no flow of charge particles, In semiconductor the current flow because of the movement of holes and electrons, if semiconductor gains energy either because of thermal agitation or by doping then the electrons can easily move from valence band to conduction band which left behind the vacant position in the valence band which is acquired by the another electron which in turn leaves behind a vacancy, this vacancy in the valence band is positively charged called as hole.
The direction of holes flow is opposite to the direction of electrons flow. In conductors the current flow because of electrons, therefore the charge carriers is very high, for insulators, there is no free charge carrier, In a semiconductor, the number of charge carriers is very less.
By providing temperature to the conductor, the number of charge carriers decreases while for insulator and semiconductor the charge carriers increases. By adding an impurity to the conductor the resistance increases which in turn decreases the conductivity.
In insulators there is no effect of adding the impurity to them, whereas semiconductor is classified as intrinsic semiconductor and extrinsic semiconductor. The pure form of the semiconductor is intrinsic semiconductor which has high resistivity, when the impurity is added to the intrinsic semiconductor then extrinsic semiconductor is obtained which is further classified as n-type semiconductor and a p-type semiconductor.
The resistance of semiconductor decreases by adding an impurity to it. At absolute zero temperature conductors behave like superconductors, Superconductors are materials which do not contain any resistivity and conduct electricity as there is no resistivity hence having infinite conductivity without losing any energy.
0コメント