MQW

Multi-quantum well (MQW) is a semiconductor heterostructure that contains multiple thin quantum wells separated by barrier layers within an active region of a device. In MQWs, electrons and holes are confined in the growth direction, forming discrete energy states and enhancing radiative transitions. The active region typically stacks several wells to increase overall recombination efficiency and to tailor the emission or absorption spectrum.

Common MQW systems include GaAs/AlGaAs and InGaAs/GaAs for infrared and visible applications, as well as InGaN/GaN for blue to green light-emitting diodes and lasers. In telecommunications, InP-based InGaAsP MQWs are used for engineered absorption and emission wavelengths. MQWs are grown by epitaxial techniques such as molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD).

Well and barrier thicknesses are chosen to achieve the desired confinement: typical well thickness is about 2–6 nanometers, barrier thickness around 5–20 nanometers, and the number of wells can range from a few to several tens. This structural control enables precise tuning of the optical bandgap, emission wavelength, and carrier dynamics. Quantum confinement enhances the oscillator strength and can improve temperature stability of emission, though in nitride-based MQWs polarization fields can lead to the quantum-confined Stark effect.

Applications span light-emitting diodes, laser diodes, photodetectors, modulators, and certain solar-cell concepts. MQWs offer advantages in wavelength engineering and efficiency but face challenges such as interface roughness, strain and defect management, and material-specific nonradiative losses.