1.8 Optoelectronic Components

Until now, on several occasions we have mentioned that the light affects the electrical properties of semiconductors. It was also mentioned that during recombination in a semiconductor, photons—quants of light—are released. It should be noted here that light usually refers to electromagnetic radiation that is detected by the human eye. In the following text, however, light will mean radiation independent of wavelength. Thanks to the aforementioned light absorption and emission phenomena, a number of semiconductor components have been developed that exhibit specific properties. They can be divided into two basic categories: those that absorb light—photodetectors and those that emit light—light sources (or light emitting devices, LED). By combining a light source and a photodetector into a single component, an element based on light coupling is obtained, which is known as an optocoupler or optoisolator. As it usually happens, a niche application of a component, during time, becomes its predominant. That we witness in both the photodetectors and LEDs. The former became a solar cell on which the future of the world’s energy system is based. The latter became a substitution to the incandescent and the noble-gas-filled lamps. In that way, optoelectronic devices affect not only electronic sensory, control, and telecommunication systems but also the energy supply and light sources all over the world. So, one may say the optoelectronic components became ubiquitous hence the attention devoted to them in this chapter. We will try here to cover most of the topics related to optoelectronics starting with basic physics, over component construction characterization and modeling, ending with some simple applications which illustrate their functionality.