In simple terms
- The term epitaxy comes from the Greek roots epi, meaning "above", and taxis, meaning "in ordered manner". It can be translated "to arrange upon".
- Epitaxy refers to the deposition of an overlayer on a crystalline substrate, where the overlayer is in registry with the substrate.
- The overlayer is called an epitaxial film or epitaxial layer.
- For most technological applications, it is desired that the deposited material form a crystalline overlayer that has one well-defined orientation with respect to the substrate crystal structure (single-domain epitaxy).
What really happens
Conceptually, MBE is the simplest process one can possibly use to create a crystalline structure. Although the growth of epi-layers happens at pressures in the 10-7-10-6 Torr, the process is conducted in an environment of ultra-high vacuum (UHV) so as to prevent contamination. The elemental sources are kept in UHV conditions with ultra-cold walls.
- Elemental sources can be switched (but not metered) nearly instantaneously
- Scaleable for reasonably high-volume production
- Very complex apparatus (up-time, cleanliness, …)
- Difficult to incorporate high vapor-pressure sources (phosphides, nitrides, II/Vis)
- Difficult to meter sources continuously