Carrier dynamics in type-II GaSb/GaAs quantum dots

The optical properties and dynamics of charge carriers in self-organized arrays of type-II (staggered band lineup) GaSb/GaAs quantum dots are studied. Interband absorption from type-II quantum dots is evidenced; the energetic positions of quantum dot absorption peaks coincide with those apparent in photoluminescence spectra. (Sb,As) intermixing with an antimony diffusion length of about 1 nm is found to make an important contribution to the observed transition energies. Dipole layer formation and quantum dot state filling contribute to the luminescence blueshift with increasing excitation density. The recombination rate of electrons with localized holes drastically depends on the average carrier density. When several carriers are localized at each dot, decay time constants around 5 ns, quite similar to type-I systems, are observed. Individual, spatially indirect excitons decay with much larger time constants close to 1 μs. The decay time of quantum dot luminescence is independent of the temperature in the measured range $T<~65\mathrm{K}$ as expected for zero-dimensional excitons.