Molecular-beam epitaxy of InSb/GaSb quantum dots

We have investigated the molecular-beam epitaxy (MBE) of InSb nanostructures on (100) GaSb substrates. We show that MBE leads to a low density (∼1-3x109 cm-2) of large islands even when varying the growth conditions on a wide range (substrate temperature ∼370-450 deg. C, growth rate ∼0.3-1.2 ML/s). Plastic relaxation takes place from the onset of island formation, regardless of the amount of InSb deposited after the two-dimensional to three-dimensional transition. These results show that In adatoms have a very long diffusion length on a Sb-terminated surface and that the energy for dislocation generation in InSb is low. This can be attributed to the low enthalpy of formation and low melting point of InSb. To circumvent this problem we have developed a MBE growth procedure based on the deposition of an amorphous InSb layer at low temperature followed by an annealing step to allow for reorganization to take place. This dramatic change of the growth conditions leads to the formation of small InSb quantum dots with a density in excess of 7x1010 cm-2. Uncapped quantum dots, however, are relaxed. In contrast, buried quantum dots are fully strained and emit near 3.5 μm at room temperature. Our results show that although formerly similar the InSb/GaSb materials system behaves completely differently from the InAs/GaAs case study system