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The growth modes of InAs on the three low index orientations of GaAs during molecular beam epitaxy (MBE) are very different, despite a constant lattice mismatch of ≈7%. Coherent three-dimensional (3D) growth occurs only on (001) surfaces; on the other two orientations strain relaxation involves misfit dislocation formation and a continuous two dimensional growth mode. Strain is therefore not a sufficient condition to induce 3D growth. Reflection high-energy electron-diffraction and scanning tunnelling microscopy observations confirm that an intermediate `wetting layer' is formed on (001)-oriented substrates prior to the formation of quantum dots. The thickness and composition of this layer is dependent on both growth temperature and the amount of InAs deposited, but it is always an (In, Ga)As alloy. We have also confirmed that substantial mass transport occurs during quantum dot formation and that the dots themselves have an alloy composition. A model to account for at least some of these effects, based on rate equations, is introduced.

Reflection high energy electron diffraction (RHEED) intensity oscillations are reported for GaAs growth by molecular beam epitaxy (MBE) on singular GaAs (110) substrates. The behavior is quite different from that observed for any other system involving a singular surface and elemental sources, in that the oscillation period is a function of temperature, flux ratio, and growth time. The results are discussed in terms of possible growth modes and relative adatom populations.

Photoluminescence (PL) , secondary-ion mass spectroscopy (SIMS), and cross-sectional transmission electron microscopy (TEM) measurements have been performed to assess surface segregation of In in GaAs during molecular-beam epitaxial growth of InAs monolayers between GaAs layers. The InAs growth temperature at which In segregation is detectable depends on the characterization technique used; using PL it is above 420 OC!, but from TEM and SIMS it is 420 and 340 "C, respectively. These results highlight the need for complementary information to provide a better understanding of the segregation phenomenon. SIMS data show that the total amount of In segregating and the extent of its distribution both increase with InAs deposition temperature.