Quantum well
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A quantum well is a potential well that confines particles in one dimension, forcing them to occupy a planar region. The width of this region is on the order of their de Broglie wavelength, leading to quantized subbands.
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.
Fabrication
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.
Applications
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.