Semiconductors and Modern Living

An Internet WebQuest on the properties and uses of semiconductors


Introduction

Over the past 150 years there have been enormous advances in communications technology, which arose from specific scientific discoveries.

In the middle of the 19th century, it was known that electricity was a form of energy which travelled along metal wires. Armed with this understanding, a communications industry was established, based on a number of inventions - including the telephone, the phonograph and the electric telegraph. By the start of the 20th century it had been discovered that electric current was carried by electrons, and a number of devices were invented which depend for their operation on the release of electrons by heating (thermionic emission). Coupled with the newly discovered electromagnetic radiation, these gave rise to a greatly expanded communications industry in which radio waves were sent through the "aether" carrying communication messages - mainly in the form of music and speech and later television images. These were transmitted, received and processed by radio "valves" and other thermionic devices.

Half a century later, quantum mechanics enabled scientists and engineers to understand the phenomenon of semiconductivity. Then in 1948 came the invention of the transistor, which overcame the limitations of the old radio valves. Almost immediately the communications industry exploded into the mass media and the information technology industry which play such a large part in life in the 21st century.


Task

Your task (as a group) is to investigate the properties of semiconductors, the history of their discovery and the contributions they have made to our modern lifestyle.

The first phase of the task, which you will do in the large group, is to investigate the electrical properties of semiconducting materials. This includes the concept of energy bands and their role in understanding the differences between conductors, insulators and semiconductors; the concept of electrons and "holes" as current carriers and the difference between n-type and p-type semiconductors; and the process of doping and how it affects the properties of semiconductors.

The second phase of the task, which you will carry out in smaller groups, is to concentrate on four of the basic signal processing functions that are performed by electronic devices - the rectification, amplification, modulation and digitization of an electrical signal; and to investigate how these functions are performed by the old-fashioned thermionic devices (radio valves) as well as by semiconductor devices ( transistors).

The third phase of the task, which you will also carry out in small groups, or individually, is to investigate one area of modern living that has been changed by the invention of semiconducting devices. These include: music recording and performance; movies, videos and DVDs; computers and industrial automation; mass communication and the internet; and modern optical technologies.


Process and Resources

In this WebQuest you will be working together with a group of students in class. Each group will address the main Task. As a member of the group you will explore web pages from groups all over the world who are involved with semiconductors and related industries or research. Because these are real web pages we're tapping into, not things made just for schools, the reading level might challenge you. Feel free to use the online Webster dictionary or one in your classroom.

You'll begin with everyone in your group getting some background before dividing into roles where people on your team become experts on one part of the topic.

Phase 1 - Background: What is a semiconductor?

 Use the web sites linked below to answer these basic questions: what are the properties of semiconductors? how do they differ from conductors and insulators? and why were they only understood in the 140s and 150s? Be creative in exploring the information so that you answer these questions as fully and insightfully as you can.

The following specific sub-tasks may guide your investigation.

  1. Describe the difference between energy levels and energy bands.
  2. Compare and contrast the electrical properties of conductors, insulators and semiconductors.
  3. Describe what is meant by a "hole" and outline its properties.
  4. Describe how the behaviour of semiconductors depends on density of electrons or holes.
  5. Identify and explain the use of germanium in early semiconductor devices.
  6. Describe how doping a semiconductor changes its electrical properties.
  7. Identify differences between p-type and n-type semiconductors.

Phase 2 - Application: What is a transistor?

Use the web sites linked below to investigate the class of electronic devices called transistors. In particular you should concentrate on how they are used to perform the following signal processing functions - the rectification, amplification, modulation and digitization of an electrical signal.

In order to understand the contributions that semiconductors have made to our society, you will need to investigate how these functions used to be performed by thermionic devices as well as by solid state devices, and to compare the efficiency of the two kinds of electronic devices in terms of size, speed, energy usage and cost.

The following specific sub-tasks may guide your investigation.

  1. Describe the operation and electrical properties of a p-n junction.
  2. Describe the operation and the general electrical properties of an n-p-n and a p-n-p junction.
  3. Describe some of the various kinds of transistors that are available today.
  4. Describe the construction of integrated circuits and microchips.
  5. Investigate the rectification of an oscillating electrical signal and how it is performed by a p-n junction.
  6. Investigate the amplification of an electrical signal and how it is performed by a transistor.
  7. Investigate the modulation of an electrical signal and how it is performed by a transistor.
  8. Investigate the digitization of an electrical signal and how it is performed by a transistor.
  9. Describe thermionic emission and the construction a radio valve.
  10. Describe how thermionic devices can be used to perform the above four signal processing functions.
  11. Compare and contrast the efficiency of thermionic and solid-state devices in terms of size, speed, energy usage and cost.

 

Phase 3 - Context: Different technologies

Individuals or pairs from your larger WebQuest team will explore one of the technological areas below. Read through the files linked to your group. If you print out the files, underline the passages that you feel are the most important. If you look at the files on the computer, copy sections you feel are important by dragging the mouse across the passage and copying / pasting it into a word processor or other writing software. Note: Remember to write down or copy/paste the URL of the file you take the passage from so you can quickly go back to it if you need to to prove your point and so that you can reference your sources in your bibliography.

Music recording and performance

Use the Internet information linked below to investigate this technological area. You should concentrate on some or all of the following items, remembering that what is important here is how these items have been changed by the development of semiconductor technologies and how these changes have affected our life styles:

  1. the recording and storage of music (microphones, long playing records, tapes, CDs, computer sound files);
  2. the performance of music (electrical and electronic instruments, synthesizers, MIDIs); and
  3. the composition of music (computers and information theory).

Movies, videos and DVDs

Use the Internet information linked below to investigate this technological area. You should concentrate on some or all of the following items, remembering that what is important here is how these items have been changed by the development of semiconductor technologies and how these changes have affected our life styles:

  1. the recording of moving images and sound (movie cameras, television cameras and camcorders);
  2. the storage of moving images (optical film, tapes, DVDs, computer files);
  3. the display of moving images (CROs, LCD screens, plasma displays).

Computers

Use the Internet information linked below to investigate this technological area. You should concentrate on some or all of the following items, remembering that what is important here is how these items have been changed by the development of semiconductor technologies and how these changes have affected our life styles: 

  1. the generation of electrical signals which carry information (analogue and digital systems, electronic transducers, light dependent resistors LDRs);
  2. the processing of information by electronic circuits (logic gates, amplifiers, integrated circuits); and
  3. the development and predicted future of computers (mainframes, personal computers, Moore's Law).

Information technology and the Internet

Use the Internet information linked below to investigate this technological area. You should concentrate on some or all of the following items, remembering that what is important here is how these items have been changed by the development of semiconductor technologies and how these changes have affected our life styles: 

  1. communicating information (Shannon's Communication Theory, electrical and electronic carriers of information);
  2. the quantification of information (bits and bytes, information and entropy, bandwidth of carriers - electrical cables and optical fibres); and
  3. the development and predicted future of the internet (connectivity, encryption and security, quantum computing).

Devices which emit and absorb light

Use the Internet information linked below to investigate this technological area. You should concentrate on some or all of the following items, remembering that what is important here is how these items have been changed by the development of semiconductor technologies and how these changes have affected our life styles:

  1. devices which absorb light (photo-electrics, LDRs, photo-voltaics, solar cells);
  2. devices which emit light (conventional lighting and LEDs, gas and solid state lasers); and
  3. devices which use light in their operation (CDs and DVDs, optical fibres);

You may explore any other technological area in which the semiconductors have made significant societal changes.


Conclusion - Debating, Discussing, and Reaching Consensus

You have all learned about a specific technological area in which semiconductors have caused significant societal change. Discuss the changes in our lives that have been brought about in this way. (One way to do this would be to examine old and modern movies for evidence of changes in lifestyle attributable to the technological areas discussed in phase 3.)




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