Recycling critical raw materials from waste electronic equipment
Recycling critical raw materials from waste electronic equipment
Recycling critical raw materials from waste electronic equipment
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<strong>Recycling</strong> <strong>critical</strong> <strong>raw</strong> <strong>materials</strong> <strong>from</strong> <strong>waste</strong> <strong>electronic</strong><br />
<strong>equipment</strong><br />
Figure 17: Operating principle of a semiconductor diode (Wikipedia, 05.12.2011, source: Use:S-kei)<br />
If the semiconductor diode is now switched into the conducting direction, electrons flow <strong>from</strong><br />
the n-doped side to the p-doped side (see Figure 17). This transition releases energy whose<br />
quantity is dependent on the crystal properties of the semiconductor used. In contrast to the<br />
simple semiconductor diodes where this energy is released in the form of lattice vibrations (=<br />
heat), in LEDs what is known as radiant transition takes place in which electromagnetic<br />
radiation is emitted. This can be in the form of infrared, visible or ultraviolet light, depending<br />
on the semiconductor band gap (see Figure 18).<br />
Figure 18: Effect of the semiconductor material used on the color of the LED light (diagrammatic)<br />
The larger the band gap, the shorter is the wavelength of the radiation emitted. However,<br />
radiant transitions only take place for specific values of some lattice parameters of the<br />
semiconductor used. These parameters are mainly produced by what are known as III-V
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