A quantum well is a three-dimensional region in a solid material where the motion of particles, such as electrons or holes, is confined in two dimensions while free to move in the third dimension. It is a structure that is typically created by sandwiching a thin layer of a different material between two layers of a different composition or bandgap.
In a quantum well, the confinement of particles in the two dimensions perpendicular to the well creates quantized energy levels, similar to the energy levels in an atom. These quantized energy levels are often referred to as "energy subbands" or "quantum states." The particles are allowed to occupy these discrete energy levels, and their motion within the well is restricted to the two-dimensional plane.
The energy levels in a quantum well are determined by the width and composition of the well and the surrounding materials. By adjusting these parameters, it is possible to tailor the energy levels to specific values, which can have various applications in electronics and optoelectronics.
Quantum wells have found extensive use in devices such as quantum well lasers, quantum well infrared photodetectors, and quantum well transistors. The confined motion of particles in quantum wells allows for control and manipulation of their properties, enabling the development of devices with enhanced performance and novel functionalities.