Semiconductors
A molecule is defined as two or more atoms of the same or different elements bound together by sharing electrons. Materials like silicone and germanium have a unique property in their atomic structure. Each has four electrons in its outermost orbital. The four electrons form perfect bonds with four neighboring atoms, creating a lattice structure.
Metals tend to be good conductors of electricity because they have free electrons, moving solely between atoms. In silicon, all of the outer electrons are bound to an electron from another atom, so they cannot move around. As there are very few free electrons are moving around silicon, they can be considered an insulator.
Doping
It is a discovery that the ability of such materials to conduct electricity can be improved, by replacing or adding certain donor or acceptor atoms to this crystalline structure, thereby producing more free electrons than holes or vice versa. The process of adding donor or acceptor atoms is known as doping. By controlling the number of impurities added makes it is possible to control its conductivity. It is why these materials came to be known as semi-conductors as they are neither total insulators nor total conductors.
There are two types of doping:
-
N-type: In this type of doping, atoms with five outer electrons are added to the lattice. While four electrons bind into the lattice, the fifth electron has nothing to bond to, so it is free to move around. By adding excess electrons, silicon can be converted into a conductor. The more doping, the higher its conductivity. Adding electrons creates a net negative charge, hence the name N-type.
-
P-type: In this type of doping, atoms with three outer electrons are added to the lattice. Its leaves are known as a hole where the fourth electron should have been to complete the bond. It creates a structure where electrons can move into these holes, and the material can conduct electricity. The absence of an electron generates a net positive charge, hence the name P-type.
The value of a semi-conductor is not derived simply by converting them from insulators to conductors. It is possible to introduce both N-type and P-type regions in the same crystal. Where two differently-doped regions exist in the same crystal creates a semiconductor junction. At these junctions, the behavior of electrons is based on modern electronics.
Semiconductor devices can display a range of useful properties, such as passing current more easily in one direction than the other, showing variable resistance and sensitivity to light or heat. The electrical properties of semiconductor material are easy to modify with just doping or the application of electrical fields or light. It further can be used for amplification, switching, and energy conversion. Before the discovery of semiconductors, vacuum Tubes were used to achieve similar functionality. A vacuum tube is a glass tube that removes all air just to a vacuum. Heating an element in a vacuum frees up its electrons. There are two elements in the tube, where the heated one, known as the cathode, and connected one to a positive voltage is known as the anode. By changing the amount of heat, the flow of electrons will change, making current and its direction controllable. Semiconductor devices have replaced vacuum tubes in most applications due to their numerous and significant advantages, including size, cost, reliability, and reduced energy consumption.
Materials
