Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA

4.2 Molecular Beam Epitaxy Technique
Figure 4.1: Schematic digram of general MBE growth chamber with its majors parts
like, eusion cells or even other types of cells like sumo and cracker cells and their
shutters, RHEED system, beam ux monitoring gauge, sample transfer manipulator,
liquid nitrogen cooled panels and substrate heater supply with speed motor for rotation.
Figure modied according to reference [33].
in the UHV range, typically in the range of 10 −9 to 10 −11 T orr, by a combination
of pumps, including ion pump, cryogenic pump, turbo molecular pump, trapping
pump and liquid-nitrogen-lled cryo shroud. The UHV environment allows deposition
with extremely low impurity concentrations and enables the use of in-situ
surface analysis tools, such as reective high energy electron diraction as illustrated
in Fig. 4.1. More importantly, it maintains source uxes in the molecular
ow regime, so that individual molecules do not collide or react with each other
before reaching the substrate referred as physical deposition, and species that
miss or desorb from the substrate are pumped away immediately.
Material sources in MBE systems are typically Knudsen eusion cells or Sumo
cells, which are loaded with ultra pure materials and dopants like group II, III and
IV materials (eg., In, Ga, Al, Be, Si) from which molecular beams are generated by
thermal evaporation or sublimation (temperature controlled cells). The elemental
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