quantumwell

A quantum well is a thin layer of semiconductor material in which charge carriers are confined in the dimension perpendicular to the layer by potential barriers formed by surrounding materials with larger band gaps. The thickness is typically on the order of a few nanometers, which causes quantization of energy levels for electrons and holes in the confined direction while allowing free motion in the plane of the well. This creates a two-dimensional electron gas with discrete subbands.

In a quantum well, the energy spectrum depends on the well width, barrier height, and the effective masses of the carriers. Narrow wells exhibit large energy spacing between subbands, while wider wells approach bulk behavior. The well and barrier materials are chosen to produce a type I or type II band alignment, controlling whether electrons and holes are confined in the same layer or separated across the interface.

Quantum wells are most commonly realized in III–V semiconductor heterostructures such as GaAs/AlGaAs or InGaAs/AlGaAs, grown by epitaxial methods like molecular beam epitaxy or metal-organic chemical vapor deposition. Precise control of thickness and interface quality is essential because interface roughness and alloy disorder broaden subbands and affect optical and electronic properties.

Applications include quantum well lasers and light-emitting diodes, quantum well infrared photodetectors, and intersubband devices such as modulators and quantum cascade lasers. Stacked multiple quantum wells enhance gain and absorption in many devices.