Semiconductor Heterojunction

a contact between two semiconductors that differ in their chemical composition. At the interface there usually is a change in, for example, the widthΔℰ of the energy gap, the mobility of the charge carriers, and the effective masses of the carriers. In abrupt heterojunctions the change in properties occurs over a distance that is comparable to or less than the width of the space-charge region. Depending on the doping of the two sides of the heterojunction, it is possible to obtain a p-n, a p-p, or an n-n heterojunction. Combinations of various semiconductor heterojunctions and p-n junctions form heterostructures.

An ideal match of crystal lattices is possible in a heterojunction only if the crystal lattices of the materials being joined coincide in their type, orientation, and spacing. Also, in an ideal heterojunction the interface must be free from structural and other defects, such as dislocations and charged centers, and from mechanical stresses. The most widely used semiconductor heterojunctions are single-crystal heterojunctions between semiconductor compounds of the type A^IIIB^V and solid solutions thereof based on arsenides, phosphides, and antimonides of Ga and Al. Since there is only a small difference between the covalent radii of Ga and Al, the change in chemical composition occurs without any change in lattice spacing. The manufacture of single-crystal semiconductor heterojunctions became possible as a result of the development of methods for the epitaxial growth of semiconductor crystals.

Semiconductor heterojunctions are used in various semiconductor devices, such as semiconductor lasers, light-emitting diodes, photocells, and optrons.