Electrical engineering - Basics Page 48

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9. Introduction into semiconductor technology

Semiconductors are mainly used for rectifying, inverting/converting, controlling, regulating, switching and amplifying voltages and currents.
This big area of application is made possible by the special chemical characteristics of some semiconductor components like e.g. germanium, silicon, gallium and arsenic (gallium arsenide).
The most important semiconductors are:

9.1 Semiconductor diodes

The PN-transition principle which has already been introduced in point 4.1 "Transistors" is also applied with semiconductor diodes. During the PN-transition a P-conducting material with an electron deficiency is brought into contact with an N-conducting material which has an electron surplus (see also diagrams 60-63).
In the contact zones of the two semiconductor materials an electron migration or electron diffusion is taking place (Latin: diffundere = penetrating). Electrons of the N-conducting side move into the "wholes" of the P-conducting side, that were created because of the electron deficiency of the P-conducting material. In turn, electrons of the P-conducting side move into the "wholes" of the N-conducting side. Through the contact zone, the so called depletion layer, which is only some thousandths of millimetres wide normally no electric current can flow.
Since by the diffusion of electrons the P-conducting material in the depletion layer is being loaded negatively and the N-conducting layer positively, a voltage is developing, the so called diffusion voltage and any further electron diffusion is stopped. The depletion layer also stops growing. The leaking diffusion voltage is very small:


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