The effect of island density on pit nucleation in In0.27Ga0.73As/GaAs films

Pit nucleation during the growth of In0.27Ga0.73As/GaAs compressively strained films was investigated under various growth conditions. In this system, pit nucleation occurs after the nucleation of three-dimensional islands, but prior to the formation of surface ripples. Island and pit size, density, area coverage and average separation were measured at various stages during growth. Pits form in regions of high local island density, and significant pit formation is correlated with a critical island separation. These results are interpreted taking into account the adatom concentration on the surface during island growth. It is postulated that adatom depletion in regions where the local island density is high, combined with local strain effects, make areas of high island density favorable sites for pit nucleation.