Start here. Creating a p-n junction

CREATING a P-N JUNCTION

Speaking

Vocabulary

8. Choose the correct spelling of these words and translate them:

diode diod	p-n juction p-n junction	anod anode	foward bais forward bias	reverse voltage revers voltag
cathode catode	curent ratin current rating	lead laed	cercuit circuit	threshold treshold

9. Work in pairs, choose one of the following questions and discuss it.

1) What is the connection between diodes and semiconductors?

2) How would you assess the importance of diodes?

3) Are vacuum tube diodes still used or are they totally replaced by semiconductors?

1. Read the text below. Match the descriptions 1- 3 with the diagrams a-c in Fig. 2.5. Put the descriptions 1-3 in logical order. Indicate the n-type and p-type regions, holes and electrons, reverse and forward bias.

a)

b)

c)

Fig. 2.5. How a p-n junction works.

A diode is a two-terminal device, having two active electrodes, between which it allows the transfer of current in one direction only. Diodes are known for their unidirectional current property, wherein, the electric current is allowed to flow in one direction.

1) Suppose you connect a battery to this little p-type/n-type junction. What will happen? It depends which way the battery is connected. If you put it so that the battery's negative terminal joins the n-type silicon, and the battery's positive terminal joins the p-type silicon, the depletion zone shrinks drastically. Electrons and holes move across the junction in opposite directions and current flows. This is called forward-bias.

2) However, if you reverse the current, all that happens is that the depletion zone gets wider. All the holes push up toward one end, all the electrons push up to the other end, and no current flows at all. This is called reverse-bias.

3) Interesting things happen when you start putting p-type and n-type silicon together. Suppose you join a piece of n-type silicon (with slightly too many electrons) to a piece of p-type silicon (with slightly too few). What will happen? Some of the extra electrons in the n-type will nip across the join (which is called a junction) into the holes in the p-type so, either side of the junction, we'll get normal silicon forming again with neither too many nor too few electrons in it. Since ordinary silicon doesn't conduct electricity, nor does this junction. Effectively it becomes a barrier between the n-type and p-type silicon and we call it a depletion zone because it contains no free electrons or holes.

That's how an ordinary diode works and why it allows an electric current to flow through it only one way. Think of a diode as an electrical one-way street.

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