A semiconductor is a substance, usually a solid chemical element or compound that can conduct electricity under some conditions but not others, making it a good medium for the control of electrical current. Its conductance varies depending on the current or voltage applied to a control electrode, or on the intensity of irradiation by infrared (IR), visible light, ultraviolet (UV), or X rays.
The specific properties of a semiconductor depend on the impurities, or dopants, added to it. An N-type semiconductor carries current mainly in the form of negatively-charged electron
Elemental semiconductors include antimony, arsenic, boron, carbon, germanium, selenium, silicon, sulfur, and tellurium. Silicon is the best-known of these, forming the basis of most integrated circuits (ICs). Common semiconductor compounds include gallium arsenide, indium antimonide, and the oxides of most metals. Of these, gallium arsenide (GaAs) is widely used in low-noise, high-gain, and weak-signal amplifying devices.
A semiconductor device can perform the function of a vacuum tube having hundreds of times its volume. A single integrated circuit (IC), such as a microprocessor chip, can do the work of a set of vacuum tubes that would fill a large building and require its own electric generating plant.
Semiconductors have had a monumental impact on our society. You find semiconductors at the heart of microprocessor chips as well as transistors. Anything that’s computerized or uses radio waves depends on semiconductors.
Today, most semiconductor chips and transistors are created with silicon. You may have heard expressions like “Silicon Valley” and the “silicon economy,” and that’s why — silicon is the heart of any electronic device.
A diode is the simplest possible semiconductor device, and is therefore an excellent beginning point if you want to understand how semiconductors work. In this article, you’ll learn what a semiconductor is, how doping works and how a diode can be created using semiconductors. But first, let’s take a close look at silicon.
Silicon is a very common element — for example, it is the main element in sand and quartz. If you look “silicon” up in the periodic table, you will find that it sits next to aluminium, below carbon and above germanium.
Carbon, silicon and germanium (germanium, like silicon, is also a semiconductor) have a unique property in their electron structure — each has four electrons in its outer orbital. This allows them to form nice crystals. The four electrons form perfect covalent bonds with four neighbouring atoms, creating a lattice. In carbon, we know the crystalline form as diamond. In silicon, the crystalline form is a silvery, metallic-looking substance.
Metals tend to be good conductors of electricity because they usually have “free electrons” that can move easily between atoms, and electricity involves the flow of electrons. While silicon crystals look metallic, they are not, in fact, metals. All of the outer electrons in a silicon crystal are involved in perfect covalent bonds, so they can’t move around. A pure silicon crystal is nearly an insulator — very little electricity will flow through it.
But you can change all this through a process called doping.