Conductors, semiconductors and insulators.

1. Match the picture with the name.

Semiconductor Conductor Dielectric (insulator)

2. Read the text about a semiconductor taken from http://en.wikipedia.org/wiki/Semiconductor

A semiconductor material has an electrical conductivity value between a conductor, such as copper, and an insulator, such as glass. Semiconductors are the foundation of modern electronics. The modern understanding of the properties of a semiconductor relies on quantum physics to explain the movement of electrons and holes in a crystal lattice. An increased knowledge of semiconductor materials and fabrication processes has made possible continuing increases in the complexity and speed of microprocessors and memory devices.

The electrical conductivity of a semiconductor material increases with increasing temperature, which is behaviour opposite to that of a metal. Semiconductor devices can display a range of useful properties such as passing current more easily in one direction than the other, showing variable resistance, and sensitivity to light or heat. Because the electrical properties of a semiconductor material can be modified by controlled addition of impurities, or by the application of electrical fields or light, devices made from semiconductors can be used for amplification, switching, and energy conversion.

Current conduction in a semiconductor occurs through the movement of free electrons and "holes", collectively known as charge carriers. Adding impurity atoms to a semiconducting material, known as "doping", greatly increases the number of charge carriers within it. When a doped semiconductor contains mostly free holes it is called "p-type", and when it contains mostly free electrons it is known as "n-type". The semiconductor materials used in electronic devices are doped under precise conditions to control the location and concentration of p- and n-type dopants. A single semiconductor crystal can have many p- and n-type regions; the p–n junctions between these regions are responsible for the useful electronic behaviour.

Some of the properties of semiconductor materials were observed throughout the mid 19th and first decades of the 20th century. Development of quantum physics in turn allowed the development of the transistor in 1948. Although some pure elements and many compounds display semiconductor properties, silicon, germanium, and compounds of gallium are the most widely used in electronic devices.

A 1 cm³ specimen of a metal or semiconductor has of the order of 1022 atoms. In a metal, every atom donates at least one free electron for conduction, thus 1 cm³ of metal contains on the order of 10²² free electrons, whereas a 1 cm³ sample of pure germanium at 20 °C contains about 4.2×10²² atoms, but only 2.5×10¹³ free electrons and 2.5×10¹³ holes. The addition of 0.001% of arsenic (an impurity) donates an extra 10¹⁷ free electrons in the same volume and the electrical conductivity is increased by a factor of 10,000.

Write the answers.

a) A semiconductor is a material between _________________________ and ________________________.

b) Metals, such as copper, aurum, silver are _____________________________________.

c) Rubber, plastic and wood are ______________________________.

d) Which chemical elements are used primarily in semiconductors? __________________________________

___________________________________________________________________________________________.

4. Watch the following video - https://www.youtube.com/watch?v=IcrBqCFLHIY and determine which of the given is an N-type semiconductor and which one is a P-type semiconductor.

______________________________ ________________________________

The process by which a semiconductor is created is called _______________________, whereas a chemical element, different from the source chemical element (usually Silicon) is added as an impurity.

Date: 2016-01-03; view: 1178