P-N Junction Diode: Definition & Properties

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  • 0:04 What's a P-N Junction Diode?
  • 1:50 How It Works
  • 2:15 P-N Junction Diode Uses
  • 3:24 P-N Junction Diode Example
  • 3:40 Lesson Summary
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Lesson Transcript
Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

Dive into this lesson to learn about how the p-n junction diode works and how it can be used. You'll also see how they control the direction of the current in a circuit.

What Is a P-N Junction Diode?

A p-n junction diode is a basic semiconductor device that controls the flow of electric current in a circuit. It has a positive (p) side and a negative (n) side. If you're reading this lesson on a computer or laptop that is plugged into an electrical outlet, then you're probably making use of such a diode right now. If you continue, you'll find out where you'll most likely find this diode.

But for now, let's talk about the makeup of a p-n junction diode. It's actually quite a simple little thing. Most of them are made with silicon which allows the diode to operate at higher temperatures, important to prevent overheating of your electronics. To make a p-n junction diode, a different impurity is added to each side of a silicon semiconductor to change how many extra holes or electrons are present. In a pure silicon semiconductor, there's an equal number of holes to electrons. If there are more holes than electrons, then that side is the p-side. If there are more electrons than holes, then it becomes the n-side. However, just because there is a positive and negative side, it doesn't mean the material is in any way electrically charged. Because the impurities have been added, the material is still electrically neutral. It's just that the added impurities either leave holes or add more free electrons.

When you place a positive side with a negative side together, you get a p-n junction which is also a p-n diode. Therefore, you get the name p-n junction diode.

On drawings, diodes are drawn with a triangle pointing to a line. The triangle acts as an arrow showing you in which direction the current is flowing. The base of the triangle is the positive side and the end with the line is the negative side of the diode. Current flows from positive to negative. If current tries to flow the other way, then the diode blocks the current, hence the line at the tip of the triangle. That's to show that if current tries to flow this direction, it won't work.

How It Works

So how does this help to control the flow of current?

If a current is flowing in the same direction as the p-n junction diode called forward bias, then things will work smoothly with the positive holes moving towards the negative side and vice versa. This keeps the current flowing. But if the current is flowing in the other direction, called reverse bias, then it forms a barrier in the middle of the semiconductor blocking the movement of the holes and electrons and stopping the flow of current.

P-N Junction Diode Uses

The ability to control the flow of current in this way makes the p-n junction diode a simple yet powerful semiconductor device. There are two big applications with these: to convert AC input to DC output and to work as a switch.

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