NUCLEATION MECHANISMS DURING MBE GROWTH OF LATTICE-MATCHED AND STRAINED III-V COMPOUND FILMS

Molecular beam epitaxy (MBE) is an ideal vehicle for the study of init ial growth processes in thin film growth, both for the degree of contr ol available in the amount of material deposited and for its compatibi lity with in situ diagnostic probes. In this paper we discuss nucleati on mechanisms involved in the growth of GaAs on GaAs and InAs on GaAs from elemental sources, in each case on the three low index substrate orientations, i.e. (001), (110) and (111)A. We have used a combination of reflection high energy electron diffraction (RHEED) and scanning t unnelling microscopy (STM) to measure both dynamic changes and nucleat ion events over the range 0.05 to 5.0 monolayers (MLs). These data hav e been analysed using scaling theory, dynamic Monte Carlo simulation a nd self-consistent rate equations. Perhaps the most important and stri king feature of the results is the uniqueness of behaviour of the (001 ) orientation in both material systems. (C) 1998 Elsevier Science B.V. All rights reserved.