Potential well

From Academic Kids

A potential well is the region surrounding a local minimum of potential energy. Energy captured in a potential well is unable to convert to another type of energy (kinetic energy in the case of a gravitational potential well) because it is captured in the local minimum of a potential well. Therefore, body may not proceed to the global minimum of potential energy, as it would naturally tend to do due to entropy.

Energy may be released from a potential well if sufficient energy is added to the system such that the local minimum is surmounted. In quantum physics, potential energy may escape a potential well without added energy due to the probabilistic characteristics of quantum particles; in these cases a particle may be imagined to tunnel through the walls of a potential well.

The graph of a 2D potential energy function is a potential energy surface that can be imagined as the Earth's surface in a landscape of hills and valleys. Then a potential well would be a valley surrounded on all sides with higher terrain, which thus could be filled with water (i.e., be a lake) without any water flowing away toward another, lower minimum (i.e. sea level).

In the case of gravity, the region around a mass is a gravitional potential well, unless the density of the mass is so low that tidal forces from other masses are greater than the gravity of the body itself.

A potential hill is the opposite of a potential well, the region surrounding a local maximum.

Quantum confinement

Quantum confinement is when electrons and holes in a semiconductor is confined by a potential well in 1D (quantum well), 2D (quantum wire), or 3D (quantum dot). That is, quantum confinement occurs when one or more of the dimensions of a nanocrystal is made very small so that it approaches the size of an exciton in bulk crystal, called the Bohr exciton radius. A quantum well is a structure where the height is about the Bohr exciton radius while the length and breadth can be large. A quantum wire is a structure where the height and breadth is made small while the length can be long. A quantum dot is a structure where all dimension are near the Bohr exciton radius, typically a small sphere.

See also

References

  • W. E. Buhro and V. L. Colvin, Semiconductor nanocrystals: Shape matters (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12612665), Nat. Mater., 2003, 2, 138 139.

Template:Physics-stubde:Potenzialtopf

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