Heterostructure

A heterostructure is a material system created by combining two or more materials with different composition or crystal structure into a single structure with an interface. The differing materials produce electronic or optical discontinuities that enable effects not present in a single material.

In semiconductors, heterostructures create heterojunctions in which conduction- and valence-band edges align differently across the interface. This yields quantum wells, barriers, and sometimes superlattices. Band alignment is commonly classified as type I (straddling), type II (staggered), or type III (broken gap). Strain from lattice mismatch can also modify electronic structure and defect formation.

Fabrication uses epitaxial growth methods such as molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), and chemical vapor deposition (CVD). Precise control of layer thickness, composition, and interface abruptness is essential for device performance.

Common material systems include III–V semiconductors such as GaAs/AlGaAs and InGaAs/GaAs, used in lasers, LEDs, and high-speed transistors. Oxide interfaces like LaAlO3/SrTiO3 host two-dimensional electron gases. Stacked two-dimensional materials, such as graphene and hexagonal boron nitride, form van der Waals heterostructures with atomically sharp interfaces.

Applications span optoelectronics and electronics, including lasers, LEDs, detectors, solar cells, high-electron-mobility transistors, and tunnel diodes. Quantum wells and quantum cascade devices exploit confinement and interfacial effects.

Challenges include lattice mismatch, interfacial defects, diffusion and intermixing, and maintaining interface quality during processing and operation.

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