Investigation of single-layer/multilayer self-assembled InAs quantum dots on GaAs_1-xSb_x/GaAs composite substrates

The structure-performance properties of single-layered and multi-layered InAs/GaAs_1-xSb_x quantum dot (QD) system, grown by molecular beam epitaxy on GaAs (001) substrates, have been investigated as a function of Sb concentration. Electron microscopy observations showed no significant crystalline defects for the single-layered InAs QDs (Sb 20%). X-ray diffraction analysis revealed that the increase of Sb concentration from 7.3% to 10.2% for the multi-layered QDs increased the strain relaxation from 0% to ∼23% and the dislocation density of GaAsSb layers went up to 3.6 × 10⁹ cm^-2. The peak energy of QD luminescence was red-shifted with increasing Sb concentration due to reduced strain inside QDs. Moreover, the carrier lifetime of the QDs was highly improved from 1.7 to 36.7 ns due to weak hole confinement as the Sb concentration was increased from 7.3% to 10.2%. These structures should be highly promising as the basis for photovoltaic solar-cell applications. Finally, the increased Sb concentration increased the thermal activation energy of electrons confined in the QDs from 163.7 to 206.8 meV, which was indicative of the improved thermal stability with Sb concentration.