Quantum well

Quantum well is a potential well that confines particles in one dimension, forcing them to occupy a planar region. The effects of quantum confinement take place when the quantum well thickness becomes comparable at the de Broglie wavelength of the carriers (generally electrons and holes), leading to energy levels called "energy subbands", i.e., the carries can only have discrete energy values.

By doping the barrier of a quantum well with donor impurities, a two-dimensional electron gas (abbreviated 2DEG) can be formed. This quasi-two dimensional system has interesting properties at low temperature, exhibiting the quantum Hall effect.

Quantum wells are formed in semiconductors by having a material, like gallium arsenide sandwiched between two layers of a material with a wider bandgap, like aluminum arsenide. These structures can be grown by molecular beam epitaxy with control of the layer thickness down to monolayers.

Because of their quasi-two dimensional nature, electrons in quantum wells have a sharper density of states than bulk materials. As a result quantum wells are in wide use in diode lasers. They are also used to make HEMTs (High Electron Mobility Transistors), which are used in low-noise electronics.