Classification of Metals, Conductors, and Semiconductors

Metals conduct heat and electricity well, whereas insulators do not. Semiconductors, on the other hand, have a conductivity that falls in between metals and insulators. The valence orbitals of the atoms in a solid interact to form a set of molecular orbitals that extend throughout the solid, according to band theory; an energy band is a continuous set of permissible energy levels. The bandwidth is the energy difference between the highest and lowest permissible levels within a band. The energy difference between the highest level of one band and the lowest level of the band is known as the bandgap. When the breadth of contiguous bands exceeds the energy gap between them, overlapping bands are formed. The energies of molecular orbitals produced from two or more types of valence orbitals are identical.

Band Theory 

There can be more than 1024 orbital interactions to consider in a 1 mol metal sample. We start with a basic one-dimensional example in our molecular orbital description of metals: a linear arrangement of n metal atoms, each holding a single electron in an s  orbital. This example is used to explain the band theory approach to metallic bonding, which assumes that the valence orbitals of the atoms in a solid interact, resulting in a set of molecular orbitals that extend throughout the solid.

Band Gap 

Because a period 3 atom’s 1s, 2s, and 2p orbitals have filled core levels, they have little interaction with the equivalent orbitals on neighbouring atoms. As a result, they form narrow bands that are well separated in terms of energy. These bands are totally filled (both the bonding and antibonding levels are populated); hence, they don’t contribute to firm bonding in any way. The bandgap is the difference in energy between the highest level of one band and the lowest level of the next. It denotes a set of banned energies that do not correlate to any of the authorised atomic orbital configurations.

Insulators 

Electrical insulators, in contrast to metals, have entire valence bands, which means they conduct electricity weakly. The energy gap between the highest filled and lowest empty levels is so great that the empty levels are inaccessible. Thermal energy cannot excite an electron from a filled to an empty level.

Semiconductors 

Devices composed of semiconductors can be utilised for amplification, switching, and energy conversion because the electrical characteristics of a semiconductor material can be adjusted by doping and the application of electrical fields or light.

In reaction to an applied electric field, electrons in the previously unoccupied conduction band are free to travel through the crystal.

When an electron in the valence band is excited, it creates a “hole” in the valence band that is equal to a positive charge. By using this method, the hole in the valence band can migrate through the crystal in the opposite direction as the electron in the conduction band.

Temperature and Conductivity 

Increased temperature increases the number of electrons with sufficient kinetic energy to be promoted into the conduction band because thermal energy can stimulate electrons across the bandgap in a semiconductor. In contrast to the behaviour of a completely metallic crystal, the electrical conductivity of a semiconductor increases fast with increasing temperature. In a metal, an electron can only travel so far before colliding with a metal nucleus as it passes through the crystal in response to an applied electrical potential. The slower the net velocity of the electron through the crystal and the lower the conductivity, the more frequent such encounters occur. The metal atoms in the lattice acquire more and more energy as the temperature of the solid rises.

Conclusions

• Gapless semiconductors and semiconductors with a small energy gap, such as 0.1 e V, have unique properties that enable them to be used in a variety of applications.
• The extraordinary sensitivity of these materials’ band structures to external effects, such as magnetic fields, electromagnetic radiation, pressure, temperature, and contaminants, underpins their utility.
• We can control the flow of conductivity in a semiconductor.
• At a certain temperature, a semiconductor can act as an insulator as well as a conductor.