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 initial growth processes in thin film growth, both for the degree of control available in the amount of material deposited and for its compatibility with in situ diagnostic probes. In this paper we discuss nucleation 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 tunnelling microscopy (STM) to measure both dynamic changes and nucleation events over the range 0.05 to 5.0 monolayers (MLs). These data have been analysed using scaling theory, dynamic Monte Carlo simulation and self-consistent rate equations. Perhaps the most important and striking 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.