A method of producing thin crystal films, in which the film composition can be carefully controlled. It relies on a number of heated sources, each of a different element, from which beams of atoms pass through an evacuated chamber and strike a crystalline target. The precise composition of the atomic layers built up on the crystal is controlled by source temperatures and systems of shutters. The method is used to produce novel semiconductor devices, such as in integrated optics and quantum Hall effect research.
Molecular beam epitaxy (MBE), is one of several methods of thin-film deposition. The process takes place in high vacuum or ultra high vacuum. The term "beam" simply means that evaporated atoms do not interact with each other or any other vacuum chamber gases until they reach the wafer, due to the large mean free path lengths of the beams. The most important aspect of MBE is the slow deposition rate, which allows the films to grow epitaxially (see island growth). However, the slow deposition rates require proportionally better vacuum in order to achieve the same impurity levels as other deposition techniques.
A computer controls shutters in front of each furnace, allowing precise control of the thickness of each layer, down to a single layer of atoms.
During operation, RHEED (Reflection High Energy Electron Diffraction) is often used for monitoring the growth of the crystal layers.
In systems where the substrate needs to be cooled the ultra-high vacuum environment within the growth chamber is maintained by a system of cryopumps, and cryopanels, chilled using liquid nitrogen to a temperature close to 77 kelvins (−196 degrees Celsius). However, cryogenic temperatures act as a sync for impurities in the vacuum, and so vacuum levels need to be several orders of magnitude better to deposit films under these conditions.
Molecular beam epitaxy is also used for the deposition of some types of organic semiconductors.
Molecular beam epitaxy was invented in the late 1960s at Bell Telephone Laboratories by J.
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