A quantum well confines electrons to specific energy levels using a thin semiconductor with a small band gap between material with a larger band gap. They are used in diode lasers and infrared imaging. Trapping electrons in this way allows for a specific manipulation of energy, producing accurate lasers for optical devices. Quantum wells are grown by molecular beam epitaxy.
A quantum well is used to confine electrons to specific energy levels. Quantum wells consist of an extremely thin semiconductor with a small band gap, resting between material with a larger band gap. They are extremely small, usually between 1 and 20 nanometers. They are most often used in diode lasers and infrared imaging.
This well uses the behavioral properties of electrons and band holes to work. Band gaps are areas in an electron orbital between the ground state, where electrons normally rest, and the conduction band, where higher energy orbital electrons move when excited. Gaps are barriers between ground-state bands and conduction bands, preventing electrons from reaching the conduction band without gaining more energy than they have in their ground states. The larger the band gap, the more energy is required for electrons to jump this gap and reach the conduction band.
Once the electron reaches the conduction band, it releases its excess energy and falls back to its ground state. By placing a microscopically thin semiconductor between material with band gaps that are too wide for electrons to skip through easily, scientists can force the electrons to stay in the thin semiconductor’s two-dimensional area. Trapping electrons in this way allows for a specific manipulation of energy.
Since electrons can only move in two directions, they can produce only the kind of energy the scientist or manufacturer wants. This energy is also concentrated in an extremely narrow stream. Because of this focus, quantum wells create accurate lasers for optical devices. A well-known example of a quantum well is in readout lasers in compact disc (CD) players.
Quantum wells are called “wells” not only for their behavior in trapping electrons like a well would trap water, but also for their appearance when represented graphically. When quantum wells are plotted on energy vs. position graphs, they look like deep valleys, or wells, often rectangular in shape. A quantum well is a type of potential well, meaning that there is a potential to produce a fixed, minimal amount of energy.
Grown, rather than created, a quantum well usually consists of material such as gallium arsenide surrounded by aluminum arsenide. Wells are grown, most often, by a process called molecular beam epitaxy, which uses an effusion cell to shoot molecules of the substance at a base substance. This method creates a single atomic layer of well material with each cell firing.
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