GaAs cap layer growth and In-segregation effects on self-assembled InAs-quantum dots monitored by optical techniques

The overgrowth of InAs islands by a GaAs cap layer has been investigated by optical in situ measurements at various growth conditions. A better smoothing of the surface has been found for low growth rates. This effect is attributed to a larger diffusion length of the gallium during growth leading to a smoother final surface. The status of the surface during and after cap layer growth can be determined from RAS and SE measurements during growth. This correlation between the optical data and the surface morphology was confirmed by ex situ AFM measurements. Post growth annealing of samples with different cap layer thickness showed indium interdiffusion from the islands to the cap layer over several nanometers. This effect is also observed during cap layer growth at higher temperatures and can be attributed to indium segregation during growth.