Semiconductors form the heart and soul of all modern electronic devices. They have enabled the creation of microprocessors and computers which, in turn, have helped humanity to make great advances in technology. Web designer will not have the necessary tools he need without it; drivers will not have the GPS system if it has never been invented. Basically, every single thing that exists today which uses some form of computer in order for it to function properly depends on semiconductors.
In order to understand how a semiconductor works, we must first examine the material which it is made of. This material is silicon, a common element that can be found in sand and quartz. Most of the semiconductor chips and transistors manufactured today are created using silicon. The element possesses a unique property in its electron structure. Like the element of carbon, it has four electrons in its outer orbital, which allows it to form crystals. These four electrons, by forming perfect covalent bonds with four neighbouring atoms, create a lattice.
In carbon, the crystalline form is the precious diamond. But, in silicon, this crystalline form is a silvery, metallic-looking substance. Though these silicon crystals look metallic, they are not actually metals. Metals have free electrons which can move easily between atoms and, since electricity involves the flow or movement of electrons, metals are good conductors of electricity. However, since silicon crystals are involved in perfect covalent bonds, their electrons cannot move around. In fact, a pure silicon crystal is almost an insulator that allows very little electricity to flow through it. So, how can these silicon crystals be used to make semiconductors whose functions depend on electricity?
A process called doping takes care of it. Doping can change the behaviour of silicon and transform it into a conductor. This is done by mixing small amounts of impurities in to a silicon crystal. There are two types of impurities that are typically used. One is N-type, where small quantities of phosphorus or arsenic are added to the silicon. Phosphorus and arsenic have five outer electrons.
The fifth electron has nothing to bond to, so it can move around. Just a small amount of impurity is enough to create free electrons that will allow an electric current to flow through the silicon. These electrons have a negative charge, thus they are called N-type. In P-type doping, either boron or gallium is introduced into the silicon lattice. Boron and gallium only have three outer electrons each, so when they are mixed into the silicon, holes are formed in the lattice where a silicon electron does not have anything to bond to. The absence of an electron creates a positive charge, which explains the name P-type.
The holes that have been formed are able to conduct current, and when it accepts an electron from a neighbour, it moves the hole over a space. So, by introducing minute amounts of either N-type or P-type doping, a silicon crystal can be transformed from being a good insulator to a conductor. Though it is still not a very good conductor when compared to metal, the silicon crystal which underwent the doping process is now able to conduct enough electricity for it to be called a semiconductor.