Initial strain relaxation and optical quality in lattice mismatched in GaAs/GaAs single quantum wells

Abstract

We have studied initial strain relaxation and optical quality in lattice mismatched InxGa1-xAs/GaAs single quantum wells as a function of In content, x, using several structural and optical characterisation techniques. Influences of cap layer thickness on material qualities were also examined. Samples were grown with solid source molecular beam epitaxy. The initial relaxation was predominated by formation of misfit dislocations for x < 0.25 and three-dimensional (3D) islands for x ⩾ 0.3. Both phenomena were observed in the transition region. Presence of misfit dislocations gave rise to degraded optical qualities in terms of luminescence efficiency and linewidth. In the case of 3D islanding, the optical signal was strong but broadened or even split into several peaks. Critical layer thickness (CLT), defined as onset of strain relaxation decreased with In content. The x-dependent CLT was explained by energy consideration. Capping a GaAs layer on a partially relaxed alloy overlayer increased the residual strain and thus improved optical qualities.