The discovery of semiconductors largely changed the course of history when it comes to technological development. Nowadays they find their application in many different areas: automotive and other industries, in making power supply systems, computers, and circuit protection devices. They also play a role in medicine, networking and communications, military, home appliances and various portable and wireless applications.
But exactly is semiconductor? It is a solid element or a compound which can act as a conductor and as an insulator, depending on the circumstances. In other words, in certain conditions it is able to conduct electricity, while in the others it is not. This feature of semiconductors plays an important role in all devices which require control of electrical current, and it is necessary in a wide variety of appliances and products.
Semiconductors have crystal structure, and their conducting properties may be adjusted by deliberately adding impurities to the structure. The addition of impurities is controlled; it reduces the semiconductor’s resistance, but creates semiconductor junctions between regions with different amount of impurities. This deliberate and controlled addition of impurities is called doping, and it determines how the semiconductor will be classified.
When it comes to the classification, there are intrinsic and extrinsic semiconductors. Those that do not contain impurities are referred to as intrinsic, and those that were doped are called extrinsic. Intrinsic semiconductors are free from all impurities and they consist of pure materials, whether they are elemental or compound. With these semiconductors, even the energy available at room temperature is enough for the electrons to cross the conjunction band. Probability of finding an electron within a material is measured on the scale from 0 to 1, and with intrinsic semiconductors this probability is 0.5. Extrinsic semiconductors are diluted or doped on purpose, in controlled conditions. The impurities differ depending on the semiconductor’s material, and they are referred to as doping agents or dopants. Dopants are chosen so they have either 3 or 5 electrons in their valence band. Those with 3 electrons are called trivalent, and those with 5 electrons are called pentavalent dopants. With semiconductors which contain trivalent dopants, the probability of finding an electron within the structure falls below 0.5. Respectively, with pentavalent dopants, it goes above the 0.5. When these two types of semiconductors are brought together, P-N junction is formed, and it is widely used in digital electronic devices.
Depending on their composition, semiconductors can be elemental and compound. Elemental semiconductors antimony, arsenic, boron, carbon, germanium, selenium, silicon, sulfur and tellurium. Most common semiconductor compounds are gallium arsenide, indium antimonide and the oxides of most metals. Gallium arsenide is a widely used compound semiconductor in all amplifying devices with low noise, high gain and weak signal.
Silicon is widely used semiconductor nowadays, applied in many areas, but mostly in the production of microprocessor chips and transistors. You have probably heard of Silicon Valley, and the silicon from the electronic chips is how this area got its name. It is the center of many silicon chip manufacturers, which is how this area got the nickname.