Reading. Ø What is a Semiconductor?

Listening

Warm-up

Contents

Ø What is a Semiconductor?

Ø Types of Semiconductors.

Ø How Semiconductors Work.

Ø Doping of Semiconductors.

1. WHAT IS A SEMICONDUCTOR?

1. “Find someone who…” activity. One student walks around the classroom and asks questions to his fellow students. If the answer is “Yes” he writes down the student’s name on the blackboard.

Ask your fellow students:

Have you ever….? Name of a fellow student

1) ….. worked on the computer?

2) ….. used a calculator?

3) ….. watched plasma TV?

4) ….. kept food in the fridge?

5) ….. talked on the cell phone?

6) ….. heated up the food in the microwave oven?

7) ….. made a presentation on the notebook?

8) …..thought what makes all these electronic devices work?

2. Listen to the text and find the answer to the question: What makes modern electronic devices work?

3. Listen to the text once more and choose among the following expressions the ones you hear:

1) Semiconductors make us feel comfortable.

2) Everybody is familiar with electricity.

3) Electronic devices are used in electronic circuits.

4) “Semi” which means not completely.

5) We use semiconductors every day.

6) Most semiconductors are crystals.

4. Let's take a closer look at semiconductors. Read the whole text and come up with the title for it.

Read the first part of the text and fill in the gaps with the words and word combinations in the box.

crystal lattice nucleus conductor electrons orbit vibrating ions copper positive ion net motion atom

All matter consists of atoms. Each (1)……………has electrons orbiting the nucleus. The (2)………………..contains the same amount of positive charge as the negative charge possessed by the orbiting electrons. The ability of any material to conduct electricity depends primarily on the behaviour of the (3)……………..in the outer orbits. Therefore, it is necessary to review briefly some aspects of solid-state physics.

In a metallic conductor such as (4)……………., the atoms are arranged in a regular array called a crystal lattice. The electrons in the outer orbits of each metal atom are only loosely bound to the nucleus. These electrons are not closely associated with any particular atom and are free to move through the (5)……………. Once an electron has left its (6)…………….round a particular atom, that atom is left with an excess positive charge. The electron-deficient atom is called a (7)……………. The electron that is now free to move is called a free electron. The free electrons in a conductor can be visualized as a cloud of electrons surrounding fixed positive ions.

At normal temperatures, the ions possess energy and vibrate. Collisions between (8)………………and free electrons cause the electrons to move in a random manner. Over a long period of time, the net motion of these free electrons is zero.

If an electric field is applied to the (9)………………, the free electrons will acquire additional energy and will tend to move in the direction dictated by the field. There will be a resulting net motion of free electrons. The (10)..................of charge carriers constitutes an electric current.

5. Read the second part of the text and put the rearranged words in the correct order.

In an insulator, (1) bound very electrons nearly tightly are all to their respective atoms. There are practically no electrons that are able to move under the influence of an applied electric field. Therefore, (2) current conduct an cannot any insulator electric under normal conditions.

As its name implies, a semiconductor (3) current is a that material conducts, but only partly. The conductivity of a semiconductor is somewhere between that of an insulator, which has almost no conductivity, and a conductor, (4) conductivity almost which full has. The conductivity of a semiconductor increases with increasing temperature, (5) of opposite metal that to behaviour a. Semiconductors can display a range of useful properties such as passing current more easily in one direction than the other.

Дата добавления: 2014-11-29