Whether you’re talking on your phone, typing on your computer, or backing up important data to your hard drive, chances are you’re taking for granted that a lot of tiny electrical components do their job right so you can do yours. Few understand in full the complexities of the circuit boards responsible for the Western way of life, but that just mean’s now is as good a time as any to learn. Here’s a brief intro to a very important electrical component: the diode.
First off, it’s important to note the difference between conductors, insulators, and semiconductors. Conductors like copper and gold are materials chemically composed in such a way that their electrons are free enough to easily carry electric charge. Insulators like plastic and wood are the opposite, as their electrons are so rigidly positioned that it is very difficult for electric charge to flow through them. Semiconductors like silicon and germanium are materials that are normally insulators, but have been transformed into conductors by a chemical process called doping.
Semiconductors altered to be slightly negatively charged are called n- (negative) type, the opposite process creating p-(positive) type semiconductors.
Say you have two silicon wafers, one of which having undergone chemical doping to become n-type and the other having undergone chemical doping to become p-type. If you put them together, some of the extra electrons in the n-type will flow towards the p-type, filling the p-type’s electron gaps. That means at either side of the junction, you’ll see normal silicon start to form. Normal silicon is an insulator, so the junction between the two types cannot conduct electricity and is called a depletion zone.
If you were to hook a battery up to this silicon sandwich with the battery’s positive side connected to the p-type end and negative side connected to the n-type end, the electric current from the battery would cause the depletion zone to shrink and electrons could flow over it, a process called forward-bias.
Hook each end to its opposite and the depletion zone gets wider to the point that no electricity can flow, a process called reverse-bias.
This process is fundamental to the utilization of a diode: it only allows an electric current to flow through it in one direction. LEDs are among the most famous of diodes; when a forward-biased current is run through them, their electrons eventually move from the n-type to the p-type and vice versa, and their combination releases a burst of energy that exists as light.
Diodes are often also used in battery-powered devices to protect the equipment if you happen to insert the battery backward. The current can only travel one way, so the device will not power on (and potentially short out) if the battery is not facing the right direction. However, diodes are not perfect and generally do let at least 10 microamps through during the reverse-biased process. If enough reverse voltage is applied, the depletion zone breaks down and the current is let through, but the voltage necessary to do that is generally a lot more than would normally be applied to the circuit.