Suppression of strain relaxation and roughening of InGaAs on GaAs using ion-assisted molecular beam epitaxy

In_xGa_1-xAs films with x=0.67 and 0.75 were grown on GaAs (001) using molecular beam epitaxy (MBE) and ion-assisted MBE. The MBE films roughened and relaxed at 2-4 monolayers, after an initial coherently strained layer-by-layer growth stage, in good agreement with previous results. Ion energies <16 eV had little effect on growth. However, increasing the ion energy from 16 to 27 eV during ion-assisted MBE decreased the rate of strain relaxation and decreased the surface roughness. For x=0.75 and ion energies ≳27 eV, relaxation was eliminated to thicknesses of 50 monolayers, well beyond the Matthews-Blakeslee prediction. We infer from the results that surface roughening of large-mismatch MBE InGaAs films allows strain relaxation well before misfit dislocations are introduced.