A SCANNING-TUNNELING-MICROSCOPY REFLECTION HIGH-ENERGY ELECTRON DIFFRACTION-RATE EQUATION STUDY OF THE MOLECULAR-BEAM EPITAXIAL-GROWTH OF INAS ON GAAS(001), GAAS(110) AND GAAS(111)A - QUANTUM DOTS AND 2-DIMENSIONAL MODES

The growth modes of InAs on the three low index orientations of GaAs d uring molecular beam epitaxy (MBE) are very different, despite a const ant lattice mismatch of approximate to 7%. Coherent three-dimensional (3D) growth occurs only on (001) surfaces; on the other two orientatio ns strain relaxation involves misfit dislocation formation and a conti nuous two dimensional growth mode. Strain is therefore not a sufficien t condition to induce 3D growth. Reflection high-energy electron-diffr action and scanning tunnelling microscopy observations confirm that an intermediate 'wetting layer' is formed on (001)-oriented substrates p rior to the formation of quantum dots. The thickness and composition o f 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 con firmed that substantial mass transport occurs during quantum dot forma tion and that the dots themselves have an alloy composition. A model t o account for at least some of these effects, based on rate equations, is introduced.