Island and pit formation during growth and annealing of InGaAs/GaAs films

Abstract

The surface morphology near the onset of 3D roughening of In_0.27Ga_0.73As/GaAs films was investigated for films both immediately after growth and after annealing. As expected, 3D island nucleation coincides with the onset of strain relaxation at a critical thickness h_c. As strain relaxation continues, pits form adjacent to 3D islands. The onset of the pit formation depends on the growth conditions, including the growth temperature and As overpressure, and the areal coverage of 3D islands. On average, pits form only after the area coverage of islands reaches ∼50%. The islands and pits coalesce into ripple arrays as the film thickness increases. Films below and above the critical thickness for 3D roughening were annealed to study the stability of islands and pits. For films with thicknesses below h_c, initially smooth surfaces evolve into islanded morphologies upon annealing. For films grown above h_c which have both islands and pits on the surface, both islands and pits grow and coalesce during annealing. These results suggest that pit formation is favored, but it requires a minimum island coverage and/or wetting layer thickness in order to nucleate.