1 – The Technology and Design of Molecular Beam Epitaxy Systems

This chapter discusses that molecular beam epitaxy (MBE) involves the generation of fluxes of constituent matrix and doping species (molecular beam) and their reaction at the substrate to form an ordered over-layer (epitaxy). To maintain the high purity and integrity of the deposit, stringent vacuum conditions are needed. A key attribute of MBE is the precision with which the composition and doping of a structure can be tailored, such that atomically abrupt features can be produced. The evaporation procedure, flux incidence on the substrate, vacuum, and process diagnostics are controlled by a supervisory operator or computer. The MBE process is supplemented by ex situ substrate preparation and wafer introduction procedures. For a better understanding of current MBE methodology and system designs, it is useful to take a brief look at the historical development of the MBE process. Retraction of sources into small volume load-lock chambers that can be isolated from the deposition chamber with a valve permits venting and reloading of the cell without disturbing the deposition environment. The integral control term corrects for offset, a condition where the system temperature stabilizes at a fixed interval below the set point temperature.