# Properties of Transistors, Diodes & Semiconductors

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• 0:01 Semiconductors
• 1:11 Properties of Semiconductors
• 2:30 Transistors
• 3:51 Diodes
• 5:01 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

When operating with an electronic system, it's important to understand how to control the flow of electricity. In this lesson, we'll look at two semiconductors, transistors and diodes, and see how they help us manage an electrical current.

## Semiconductors

Imagine that you controlled a major river that people used for shipping various things. Sort of like the Panama Canal, but even way more awesome and important - the super highway of water. Now, as the person in charge of this waterway, you need to be able to control which ships can go where to keep them from colliding. This means controlling the current, the direction of flow so that things go where you need them. This same idea can be applied to electronics. When working with complex systems of currents, it's pretty useful to be able to control the direction and strength of various electrical currents.

Some of the most important tools for this are semiconductors, generally crystalline solids with specific electrical characteristics. Basically, in electronics, semiconductors are devices made of a specific material that help you control currents, similar to how a dam or reservoir or lock is used to control waterways. It's all part of a larger system to help you control currents because you can't always just go with the flow.

## Properties of Semiconductors

So, let's look at our semiconductor materials a bit more closely. What makes them so special? The answer is in their resistance, or the degree of difficulty passing an electrical current through a material. Now semiconductors reduce in resistance as their temperature increases. That's important. Have you ever touched an electronic device that's been running for awhile? It's hot, right? Electricity is energy, which means it generates heat. We all know that metal conducts electricity well but as the temperature of metal increases, so does its resistance. That's why semiconductors are so great - the hotter they get, the less resistant they are and the better they are at conducting electricity.

But that's not the only great thing about them. Impurities can be added to the crystalline structures of a semiconductor to intentionally block, redirect, or change the direction of electrical currents. So semiconductors give you a lot of control over how electricity passes through a system.

The most common semiconductor material used in modern electronics is silicon, which is not only abundant and easy to process, but is sturdy and conducts electricity in a very controlled way.

## Transistors

Now that we know what semiconductors are, how do we actually use them? One of the major uses of semiconductors is to make transistors, semiconductors used to control or amplify electrical currents. Basically, a transistor is a switch that is controlled by an electrical signal. When the transistor is turned on, the current flows freely. When it's turned off, the current stops. Transistors can also be opened a little so that the current is reduced or amplified to increase the output of electrical signals.

Developed in 1947 by American physicists John Bardeen, Walter Brattain, and William Shockley, these little devices are amongst the important inventions of the 20th century. They are used in practically every electronic device in the modern world and are the reason that things like computers and even radios, can be made so small.

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