bandoffset

Band offset, also referred to as bandoffset, is the difference in energy between the band edges of two materials at a semiconductor heterojunction. When two semiconductors are brought into contact, their conduction-band minima and valence-band maxima realign to form a potential step, creating a conduction-band offset and a valence-band offset.

These offsets determine the type of band alignment: type I, type II, or type III, which in turn controls carrier confinement and recombination, as well as leakage barriers in devices such as quantum wells and heterojunction transistors.

Practically, ΔEc and ΔEv are related by ΔEc + ΔEv ≈ Eg1 − Eg2, where Eg1 and Eg2 are the band gaps of the two materials. In ideal models such as Anderson's rule they can be estimated from electron affinities and ionization energies, but real interfaces exhibit dipoles and interfacial states that modify the offsets. Offsets are determined experimentally by spectroscopy methods like X-ray photoelectron spectroscopy or ultraviolet photoelectron spectroscopy, as well as by capacitance-voltage or photoluminescence measurements; theory uses first-principles calculations and empirical fitting.

Band offsets are central to the design of optoelectronic devices, including quantum-well LEDs and lasers, high-electron-mobility transistors, and solar cells, where the offset controls carrier confinement and transport across the interface. They are affected by interface quality, lattice mismatch, temperature, and alloy composition, and can vary with growth conditions.