A double heterostructure, sometimes called ''double heterojunction'', is formed when two
semiconductor
A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
materials are grown into a "sandwich". One material (such as
AlGaAs
Aluminium gallium arsenide (also gallium aluminium arsenide) ( Alx Ga1−x As) is a semiconductor material with very nearly the same lattice constant as GaAs, but a larger bandgap. The ''x'' in the formula above is a number between 0 and 1 - this ...
) is used for the outer layers (or
cladding), and another of smaller
band gap (such as
GaAs
Gallium arsenide (GaAs) is a III-V direct band gap semiconductor with a zinc blende crystal structure.
Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monolithic microwave integrated circui ...
) is used for the inner layer. In this example, there are two AlGaAs-GaAs junctions (or boundaries), one at each side of the inner layer. There must be two boundaries for the device to be a double heterostructure. If there was only one side of cladding material, the device would be a simple, or single,
heterostructure.
The double heterostructure is a very useful structure in
optoelectronic devices and has interesting electronic properties. If one of the cladding layers is
p-doped, the other cladding layer n-doped and the smaller energy gap semiconductor material undoped, a
p-i-n structure is formed. When a current is applied to the ends of the pin structure,
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no kn ...
s and
holes
A hole is an opening in or through a particular medium, usually a solid body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of en ...
are injected into the heterostructure. The smaller energy gap material forms energy discontinuities at the boundaries, confining the electrons and holes to the smaller energy gap semiconductor. The electrons and holes
recombine in the
intrinsic semiconductor emitting
photons
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they alway ...
. If the width of the intrinsic region is reduced to the order of the
de Broglie wavelength
Matter waves are a central part of the theory of quantum mechanics, being an example of wave–particle duality. All matter exhibits wave-like behavior. For example, a beam of electrons can be diffracted just like a beam of light or a water wave ...
, the energies in the intrinsic region no longer become continuous but become discrete.
(Actually, they are not continuous but the energy levels are very close together so we think of them as being continuous.) In this situation the double heterostructure becomes a
quantum well.
References
{{DEFAULTSORT:Double Heterostructure
Semiconductor structures