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MODULE V
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:
- Diodes
- Rectifiers
- Transistors
- Thyristors
- Triacīs
- Magnet-dependent semiconductor
components (e.g. hall generators)
- Opto-electronic semiconductor
components (e.g. photo resistors, solar cells)
- Integrated circuits
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:
- with germanium it is
between 0,2V-0,4V
- with silicon it is
between 0,5V-0,8V