High School Physics

# Semiconductors, doping, N-type and P-type, motion of electron & hole

In a semiconductor, electrons flow, but not as well as they do in a conductor. Some semiconductors carry electrons almost as well as good electrical conductors like copper or aluminum; others are almost as bad as insulating materials. Semiconductors are not exactly the same as resistors. In a semiconductor, the material is treated so that it has very special properties.

## Doping

The semiconductors include certain substances, such as silicon, selenium, or gallium, that have been “doped” by the addition of impurities like indium or antimony.

## motion of electrons and holes

Electrical conduction in gallium arsenide, metal oxides, or silicon rectifiers is always a result of the motion of electrons.

However, this can be a quite peculiar movement, and sometimes engineers speak of the movement of holes rather than electrons.

A hole is a shortage of an electron—you might think of it as a positive ion—and it moves along in a direction opposite to the flow of electrons (Fig. 1).

## Majority or minority type of carrier

In a semiconductor, the more abundant type of charge carrier is called the majority carrier. The less abundant kind is known as the minority carrier.

## N-type and P-type semiconductore

When most of the charge carriers are electrons, the semiconductor is called N-type, because electrons are negatively charged. When most of the charge carriers are holes, the semiconducting material is known as P-type because holes have a positive electric charge.

But P-type material does pass some electrons, and N-type material carries some holes.

## Use of semiconductor

Semiconductors are used in diodes, transistors, and integrated circuits in almost limitless variety. These substances are what make it possible for us to have a computer in the form of a desktop or laptop.

That notebook computer, if it used vacuum tubes, would occupy huge space, because it has billions of electronic components. It also would cost thousands of dollars in electric bills every day. But the circuits are etched microscopically onto semiconducting wafers, greatly reducing the size and power requirements.

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