Heterojunction

A heterojunction is an interface between semiconductors with different compositions or band structures. Its band alignment can control the movement and separation of charge carriers.

Band alignment: The relative positions of the energy bands in materials placed in contact. The offset between the two semiconductors determines which carriers can cross the interface.
Semiconductor: A material whose electrical conductivity lies between that of a conductor and an insulator and can be controlled. Heterojunctions join two members of this broad material class.
Heterojunction bipolar transistor: A bipolar transistor whose emitter and base use semiconductors with different band gaps. Its emitter heterojunction improves carrier injection and enables high-speed operation.
Homojunction: A junction between regions of the same semiconductor, often with different doping. Unlike a heterojunction, it does not join distinct semiconductor compositions.
Conduction band: The range of electron energy states in a solid where electrons can move through the material. Its edge helps define the electron barrier at a heterojunction.
Semiconductor heterostructure: A structure made by combining distinct semiconductor layers or regions. A heterojunction is the interface within such a structure.
Heterojunction solar cell: A photovoltaic cell that uses an interface between different semiconductor materials to collect photogenerated carriers. Its junction can separate carriers while limiting recombination.
Schottky barrier: An energy barrier formed at a metal–semiconductor contact. It is a related interface barrier, but one side is a metal rather than another semiconductor.
Valence band: The highest range of electron energy states normally occupied in a solid. Its edge helps define the hole barrier and carrier separation.
Band gap: The energy range in a solid between its valence-band maximum and conduction-band minimum where no electronic states occur. Different band gaps are a key source of heterojunction band offsets.

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