Molecular-beam epitaxy

[1] MBE is used to make diodes and MOSFETs (MOS field-effect transistors) at microwave frequencies, and to manufacture the lasers used to read optical discs (such as CDs and DVDs).

The most important aspect of an MBE process is the deposition rate (typically less than 3,000 nm per hour) that allows the films to grow epitaxially (in layers on top of the existing crystal).

The absence of carrier gases, as well as the ultra-high vacuum environment, result in the highest achievable purity of the grown films.

In solid source MBE, elements such as gallium and arsenic, in ultra-pure form, are heated in separate quasi-Knudsen effusion cells or electron-beam evaporators until they begin to slowly sublime.

In other systems, the wafers on which the crystals are grown may be mounted on a rotating platter, which can be heated to several hundred degrees Celsius during operation.

Oxygen sources, for example, can be incorporated for depositing oxide materials for advanced electronic, magnetic and optical applications.

One of the achievements of molecular-beam epitaxy is the nano-structures that permit the formation of atomically flat and abrupt hetero-interfaces.

[8] These heterostructure nanowire lasers are only possible to build using advanced MBE techniques, allowing monolithical integration on silicon[9] and picosecond signal processing.

A simple sketch showing the layout of the main chamber in a molecular-beam epitaxy system
One-atom-thick islands of silver deposited on the (111) surface of palladium by thermal evaporation. The substrate, even though it received a mirror polish and vacuum annealing, appears as a series of terraces. Calibration of the coverage was achieved by tracking the time needed to complete a full monolayer using tunneling microscopy (STM) and from the emergence of quantum-well states characteristic of the silver film thickness in photoemission spectroscopy (ARPES). Image size is 250 nm by 250 nm. [ 7 ]
Molecular beam epitaxy system Veeco Gen II at the FZU – Institute of Physics of the Czech Academy of Sciences . The system is designed for growth of monocrystalline semiconductors, semiconducting heterostructures, materials for spintronics and other compound material systems containing Al , Ga , As , P , Mn , Cu , Si and C .