Potential well

A potential well is the region surrounding a local potential energy minimum. 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.

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

• a Graphical representation of a potential well

References

• W. E. Buhro and V. L. Colvin, Semiconductor nanocrystals: Shape matters, Nat. Mater., 2003, 2, 138 139.