Spatially direct and indirect optical transitions observed for AlInAs/AlGaAs quantum dots

The effects of the Aluminium concentration on the emission of Al0.45In0.55As/AlyGa1−y As quantum dots (QDs) are investigated by photoluminescence (PL), with the excitation power density as a variable parameter. The influence of a varying barrier composition on the QD emission is investigated theoretically and discussed with respect to PL measurements. For the highest barrier composition value (y = 0.77), we interpret the QD emission as originating from indirect type-II transitions involving electrons in the barrier X valley and heavy holes (HH), with S and P symmetry, in Al0.45In0.55As QDs. The PL spectra of the y = 0.38 sample exhibits three lines: two of them are related to indirect type-II transitions, in which the electron ground state belongs to the indirect gap (L and X) minima in the barrier conduction band, whereas the third transition is attributed to a direct type-I transitions.