Book contents
- Frontmatter
- Contents
- List of figures
- List of tables
- Acknowledgements
- Introduction
- Part I The technology – how electronic devices work – digital systems and software
- Part II Innovators, entrepreneurs, and venture capitalists
- Part III Global reach, global repercussions
- Appendix 1.1 Smaller, faster, more efficient MOSFETs
- Appendix 1.2 Building multi-transistor logic gates
- Appendix 1.3 MOSFETs in memory devices
- Appendix 1.4 CMOS reduces logic gate power dissipation
- Appendix 1.5 Laser diode basics
- Appendix 1.6 Light-emitting diodes (LEDs)
- Appendix 1.7 Photodetectors
- Appendix 1.8 Making fiber optic cables
- Appendix 1.9 Principles of LCD displays
- Appendix 2.1 The demise of analog computers
- Appendix 2.2 IP, TCP, and the Internet
- Appendix 2.3 Building an object-oriented program
- Index
Appendix 1.6 - Light-emitting diodes (LEDs)
Published online by Cambridge University Press: 07 December 2009
- Frontmatter
- Contents
- List of figures
- List of tables
- Acknowledgements
- Introduction
- Part I The technology – how electronic devices work – digital systems and software
- Part II Innovators, entrepreneurs, and venture capitalists
- Part III Global reach, global repercussions
- Appendix 1.1 Smaller, faster, more efficient MOSFETs
- Appendix 1.2 Building multi-transistor logic gates
- Appendix 1.3 MOSFETs in memory devices
- Appendix 1.4 CMOS reduces logic gate power dissipation
- Appendix 1.5 Laser diode basics
- Appendix 1.6 Light-emitting diodes (LEDs)
- Appendix 1.7 Photodetectors
- Appendix 1.8 Making fiber optic cables
- Appendix 1.9 Principles of LCD displays
- Appendix 2.1 The demise of analog computers
- Appendix 2.2 IP, TCP, and the Internet
- Appendix 2.3 Building an object-oriented program
- Index
Summary
Semiconductor light emitting devices are grouped into two categories:
Light emitting diodes (LEDs), which are basically general-purpose replacements for vacuum tube-based light emitters.
Laser diodes that emit sharply focused monochromatic light beams.
We have already discussed laser diodes. Here we will look briefly at LEDs, which have come to dominate important segments of the lighting industry.
Light emitting diodes consist of p-n junctions in a special class of semiconductors that are capable of emitting light of many colors ranging from the infrared into the violet. Furthermore, of great practical importance is the fact that by combining LEDs of red, blue, and green, or using special phosphor coverings, white light can be produced, with conversion efficiencies from electrical input to useful light output that are very competitive with conventional vacuum-based devices.
When we discussed p-n junctions, we noted that one of their most valuable properties is their ability to inject carriers across the p-n interface. This is the principle behind LEDs. When forward-biased, they emit various colors of light, ranging from the blue into the infrared, depending on the semiconductor materials used.
Semiconductors useful as LEDs and lasers have special structures. As noted earlier when we discussed lasers, they are direct bandgap materials. Within them the recombination of an injected electron with a hole (in effect the capture of the free electron by an empty spot in the atomic outer orbit) results in the release of energy in the form of a photon. A photon is a unit of light energy.
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- Competing for the FutureHow Digital Innovations are Changing the World, pp. 367 - 369Publisher: Cambridge University PressPrint publication year: 2007