How do semiconductors work


Semiconductors - functionality and practical examples

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Electrical conductors are required to transport electricity from the place of generation to the end consumer. Every conductor has an electrical resistance, which is a quantity that provides information about the resistance a conductor has to a charge transport. With the same voltage, the greater this resistance, the lower the current flow through the electrical conductor. There are three important groups of electrical conductors in electrical engineering. The first are conductors that are made of material that has comparatively good conductivity, usually made of metal. They contain free electrons that serve as charge carriers. There are also so-called non-conductors, although the term is a bit misleading, as there are no ideal non-conductors. Non-conductors consist of substances that have a specific resistance of more than 104 Ω mm2/ m because there are no free electrons in them. Their importance as insulators in electrical engineering is immense. The third group is made up of semiconductors. In the initial state, there are no free electrons in them, so that they initially have properties similar to those of the dielectric. External electrons, however, can detach themselves from the atoms to which they are bound due to external influences such as temperature, light or electrical fields. As a result, semiconductors then take on the properties of conductors.1 How electrical semiconductors work.1

How electrical semiconductors work

For example, a rising temperature can influence electrical semiconductors. The electrons begin to vibrate, every now and then one of them loosens from its bond to the atom. A positively charged gap is created at the point where the electron was. If a neighboring electron wanders into this gap, this ultimately leads to a current flow, as the positive charge continues to move. The conductivity of electrical semiconductors is based on both negative and positive charge carriers. When an electric field is generated, the negatively charged electrons migrate to the positive pole and the positively charged holes or defect electrons to the negative pole. Electrical semiconductors are important for electrical engineering primarily because of the so-called doping. Small amounts of foreign atoms are introduced into the electrical semiconductor. These either bring in additional electrons or holes. If electrons or donors are introduced, the result is an n-doped semiconductor structure. In cases in which holes or acceptors are added, p-doping results. The substance silicon is given as an example of a semiconductor. Silicon has four outer or valence electrons. Therefore, a crystal lattice with a covalent bond can form. If, for example, phosphorus atoms are added that have five outer electrons, one free electron remains. This increases the conductivity of the silicon. Electrical semiconductors are the basis for numerous components, such as transistors and diodes. In addition to silicon, there are other semiconductor materials such as germanium and gallium arsenide.2

Examples of semiconducting components in practice

Electrical semiconductors are ideally suited for computer chips, for example. The disadvantage is that materials such as silicon, germanium and gallium arsenide are quite brittle and break relatively easily when they are exposed to mechanical stress. Due to their crystalline inorganic structure, they cannot be deformed by more than one percent. These semiconductors are therefore impractical for the manufacture of electrical modules. Organic semiconductors are significantly more malleable. However, a research team from the Chinese Academy of Sciences in Shanghai has discovered an inorganic compound that is similarly flexible: silver sulfide is ideal for flexible electronic components. The inorganic semiconductor is already used in some electronic circuits, and the discovery of silver sulfide as an electrical semiconductor could also have a positive influence on the pace of development of flexible electronic modules.3 Semiconducting carbon nanotubes are also an advance in computer technology. So far, circuits in processors have been made of silicon. With the help of carbon tubes, a new type of processor could be developed that would be both smaller and more energy efficient than previous processors.4 The semiconductor quantum voltage source is another example of technical progress through semiconductors. Before its development, quantized voltages could only be realized in superconducting circuits with the aid of the Josephson effect. In the Physikalisch-Technische Bundesanstalt (PTB), a quantized voltage was generated on a semiconductor chip by connecting a single electron pump, quantized current sources based on semiconductors and a quantum Hall resistor. Interestingly, the output voltage of the semiconductor quantum voltage source corresponds to that of a superconducting Josephson circuit, although it is generated by a completely different physical effect. In the future, the output voltage of the semiconductor quantum voltage source is to be increased significantly so that it can be used for experiments such as the conclusion of the metrological triangle.5