Two-dimensional electron gas
A two-dimensional electron gas (2DEG) is the occurrence of metallic electrons in a semiconductor - hetero structure , in which the electrons can move effectively in only two dimensions. Many effects occur in 2DEGs that do not occur in three-dimensional systems , for example the quantum Hall effect .
The freedom of movement of the electrons can also be restricted to even fewer dimensions:
- A restriction to one dimension results in quantum wires .
- A restriction to zero dimensions is called a quantum dot , sometimes also called a designer atom .
generation
2DEGs can be generated by applying two semiconductor layers with significantly different band gaps and different Fermi levels to one another. In order to compensate for the different Fermi energies, some electrons flow onto the other semiconductor at the boundary layer , thereby creating a local electric field . As a result, there can be an energy minimum in the conduction band that is relatively sharply limited to the boundary layer. Electrons that are in this minimum do not have enough energy to leave it.
Since this energy minimum is very narrow perpendicular to the boundary layer, it follows from quantum mechanics that the movement in this direction is quantized with a relatively large energy difference between the ground state and the first excited state . On the other hand, the movement parallel to the plane is practically not restricted and therefore has a quadratic energy dispersion typical of electron gases. As long as the kinetic energy is below the excitation energy for the first excited state perpendicular to the boundary layer, the electron is therefore limited to only two degrees of freedom .
Individual evidence
- ^ Siegfried Hunklinger: Solid State Physics . 5th, act. Edition. De Gruyter Oldenbourg, Berlin 2018, ISBN 978-3-11-056774-8 , pp. 367 f., 401, 465 ( limited preview in Google Book search).