Physical principles of ultrahigh vacuum atomic layer epitaxy

A concise discussion concerning physical principles of the UHV ALE is presented in this paper. Emphasis is put on the kinetic processes occurring in the near surface transition layer (NSTL) during the growth of semiconductor compounds. The NSTL is considered here as a model for the growth region in which UHV ALE takes place. This model is based on the following assumptions: (i) for anions and for cations, constituents of the grown semiconductor compound, transition layers, intermediate between the well-ordered crystalline substrate (epilayer) and the gaseous, disordered phase of the impinging beams are created in the ALE process, (ii) after desorption, during the dead times in the ALE deposition cycle, of the loosely bound anions or cations, also a part of the first atomic monolayer of these constituents (nearest to the substrate/epilayer surface), desorb into the UHV environment. With the NSTL model of UHV ALE all most important features, characteristic to this growth technique, can be explained in a satisfactory way.