Semiconductor Materials
Conductor
A material that allows electric current to flow easily due to the presence of many free electrons (e.g., copper, aluminum).
The term conductor applied to any maerial that will support a generaous frow of charges when the voltage is applied acrosd its terminals.
Metals like copper and aluminum have no forbidden gap between the valence band and the conduction band. The two bands overlap.
Insulator
A material that resists the flow of electric current because it has very few or no free electrons (e.g., rubber, glass).
An insulator is a material that offers a very low level of conductivity when voltage is applied.
Semiconductor
A material whose conductivity lies between that of a conductor and an insulator, and can be controlled by doping or temperature (e.g., silicon, germanium).
Band Theory
Energy Band: In a solid, the closely packed atoms cause their atomic energy levels to merge into continuous ranges called energy bands. The main ones are the valence band (filled with bound electrons) and the conduction band (where electrons move freely).
Covalent Bonding: It’s the sharing of valence electrons between neighboring atoms to achieve stability. In semiconductors like silicon, each atom shares four electrons with four neighbors, forming strong covalent bonds that hold the crystal lattice together.
Valence Band: The energy band that contains the outermost (valence) electrons bound to atoms. These electrons are responsible for forming chemical bonds and cannot move freely unless they gain enough energy.
Conduction Band: The higher energy band where electrons are free to move within the material, allowing electric current to flow. Electrons must gain enough energy to jump from the valence band to this band.
Forbidden energy gap: The gap between valance band and energy band.