There are two properties of crystals which are of particular interest to me with regards to semiconductors which calculates the current in a semiconductor and they are:
1. Number of fixed and mobile charges present in the material.
2. The transport of mobile carriers through the semiconductor.
This two properties are the reason why I mentioned crystals in the first place.
Now, conductors have something that is totally opposite to that of semiconductors that I would like to mention and that is its TEMPERATURE COEFFICIENT.
Conductors have a positive temperature coefficient and I am going to explain this for you now.
When I say that conductors have a positive temperature coefficient am only trying to say that an increase in temperature leads to an increase in the resistance of the conductor.
For Example: When I heat a copper rod, the flow of current through that copper rod is reduced.
Therefore, the temperature applied to a conductor is directly proportional to the resistance of the flow of current through that conductor.
The reverse of this occurs in the semiconductors. Semiconductors have a negative temperature coefficient. Just like I explained above this means that an increase in temperature applied to a semiconductor leads to a decrease in resistance.
Silicon is an example of a semiconductor.
So what I am trying to say is that when a silicon is being heated the passage of current through that silicon is increase because the resistance is reduced.
Therefore, the temperature applied to a semiconductor is inversely proportional to the resistance of the semiconductor.
Here is what I understand about semiconductors, Semiconductors are solid materials that behaves as an insulator at absolute zero temperature (0K) and at higher tempertures act as a conductor.
The conductivity of a semiconductor can be greatly increased by the addition of impurities basically known as doping and photoconductivity.
Photoconductivity is process whereby a semiconductor material absorps light of a certain wavelength to improve its conductivity.
There are two basic types of Semiconductors which are:
1. Element Semiconductors
2. Compound Semiconductors
Element Semiconductors are those conductors that consists of just one element mainly in the group 4 of the periodic table. For Example Silicon (Si), Germanium (Ge) etc.
Compound Semiconductors are those conductors that comprises the combination of two or more elements to form a compound. This is basically the combination of group 3 and group 5 elements like Gallium Arsenide (GaAs) and Indium Phosphide (InP). and the combination of group 2 and group 6 elements like Zinc Sulphide (ZnS) and Cadmium Selenide (CdSe).
As you already know in the world of semiconductors silicon is mostly used that germanium.
Below I outlined some reasons for that:
1. Silicon is abundant in nature therefore, it is readily available and cheap.
2. Silicon is non-toxic and light weight.
3. Silicon forms a better dielectric interface than germanium.
4. Silicon could be operated at higher temperatures than germanium.
5. Silicon forms a stable oxide that is used as a passivation layer during the fabrication of integrated circuits.
Among the compound elements, Gallium Arsenide and Indium Arsenide are the most widely used.
For the production of LEDs, laser diodes, solar cells, microwave integrated circuits etc GaAs is used but it has a setback which is its difficulty to form large diameter rods called ingots that limits the wafer diameter to sizes significantly smaller than silicon.
Lastly, there are two classifications of semiconductor devices which are:
1. Active Semiconductor Devices
2. Passive Semiconductor Devices
The difference between the two is that active semiconductor devices has at least one pn junction while passive semiconductor devices do not have any pn junction.
Examples of active semiconductors are: Transistors, Diodes, Rectifiers etc
Examples of passive semiconductors are: Resistors, Inductors, Capacitors etc.
