Self-formation of ultrahigh-density (1012 cm−2) InAs quantum dots on InAsSb/GaAs(001) and their photoluminescence properties

InAs quantum dots (QDs) with an ultrahigh density of 1 × 1012 cm−2 were fabricated on a 1.25-monolayer-thick InAsSb wetting layer on a GaAs(001) substrate by molecular beam epitaxy. QD formation was initiated by small two-dimensional InAsSb islands. Coalescence and ripening effects involving neighboring QDs were suppressed. Photoluminescence spectra of the QDs shifted continuously to higher energies with increased optical excitation power. This was attributed to the filling of inhomogeneous ground states via tunneling between QDs. Indirect transitions in a type-II band structure were observed for small QDs. In large QDs, direct transitions were also observed at high optical excitation levels.