Molecular beam epitaxy
<Abstract>
Molecular beam epitaxy (MBE) is a process for growing thin, epitaxial films of a wide variety of
materials,ranging from oxides to semiconductors to metals. It was first applied to the growth
of compound semiconductors.That is still the most common usage, in large part because of
the high technological value of such materials to theelectronics industry. In this process
beams of atoms or molecules in an ultra-high vacuum environment are incidentupon a heated
crystal that has previously been processed to produce a nearly atomically clean surface.
The arriving constituent atoms form a crystalline layer in registry with the substrate, i.e., an
epitaxial film. These films areremarkable because the composition can be rapidly changed,
producing crystalline interfaces that are almost atomically abrupt. Thus, it has been possible
to produce a large range of unique structures, including quantum well devices,superlattices,
lasers, etc., all of which benefit from the precise control of composition during growth.
Because of the cleanliness of the growth environment and because of the precise control
over composition, MBE structures closely approximate the idealized models used in solid
state theory.
This discussion is intended as an introduction to the concept and the experimental procedures
used in MBE growth. The refinement of experimental procedures has been the key to the
successful fabrication of electronically significant devices, which in turn has generated the
widespread interest in the MBE as a research tool. MBE experiments have provided a wealth
of new information bearing on the general mechanisms involved in epitaxial growth, since
many of the phenomena initially observed during MBE have since been repeated using other
crystal growth processes. We also summarize the general types of layered structures that have
contributed to the rapid expansion of interest in MBE and its various offshoots. Finally we
consider some of the problems that remain in the growth of heteroepitaxial structures, specifically,
the problem of mismatch in lattice constant between layers and between layer and substrate.
The discussion is phenomenological, not theoretical; MBE has been primarily an experimental approach based on simple concepts.