The term semiconductor refers to a material that exhibits some level of conductance ability and acts as a mediator between both conductors and insulators; its conductivity is between that of a conductor and an insulator. This implies that there is definitely a relation between conduction properties of semiconductors. Let us explore it.
Band Structure
In semiconductors the forbidden gap between the conduction band and the valence band is small. At OK, the valence band is completely filled and the conduction band may be empty. But when a small amount of energy is applied, the electrons easily moves to the conduction band. Under normal circumstances silicon act as a poor conductor. Each silicon atom is bonded to 4 other silicon atoms. The bonds between these atoms are co valent bonds where the electrons are in fixed positons. So at OK, the electrons does not move within the lattice structure.
Conductivity
Through measurement of the conductivity of the material, we get a rough idea of how much the material can conduct electricity through it. Electrical conductivity largely depends upon the amount of the electrons available for conduction. Importance of conductivity is very much in many engineering applications such as medical electronics.
Variation in Semiconductors
In the case of semiconductor materials, conductivity increases with temperature; that is, increase in conduction current with rise in temperature takes place owing to the increase in broken covalent bonds, which results in an increased number of charge carriers for the current to flow. Thus, more electrons from the Valence Band cross over to the Conduction Band as the temperature rises. The conductivity of semiconductors is reversible to that of metals.
Electrical Resistivity
Specific electrical resistance or volume resistivity is the generic term used to refer to resistivity. It defines the intrinsic property of a material with the ability to oppose the flow of current. Another possible definition is the resistance of a conductor with unit length and unit cross-sectional area. Hence, resistivity does not depend on the length and the area of cross section of the material; it depends only on the length and area of cross section of the material to determine its resistance. The resistivity may be expressed as p = R A/L, where R is resistance in ohms, A is area of cross section in square meters and L is length in meters. The unit for resistivity is ohm meter.
Variation in Semiconductors
When the temperature is increased, the forbidden gap between both bands decreases and the electrons transfer from the valence band to the conduction band. So, many electrons are free to move through the structures from the covalent bonds in between Si atoms. This will increase the conductivity of the material. Thus, with the increase in temperature in a semiconductor, the charge carrier density also increases and results in the decrease in resistivity. It is said that the semiconductors are having negative temperature co-efficient. Thus, the temperature co-efficient of resistivity, a, is negative. The graph is thus non-linear over a wide range.
The conduction properties of Semiconductors help serve them for such electronic devices as LEDs, solar cell, etc. Life would be complicated and diverse without these semiconductors. Semiconductor materials are mainly because of their moderately controllable conductance that can be changed by doping. Semiconductors have their unique qualities, which favor making numerous devices from them.
