Dispersion of photoluminescence peak positions in asymmetric InAs QD multi quantum well structures

The photoluminescence and its temperature dependences have been investigated for InAs quantum dots (QDs) embedded in asymmetric GaAs/In_xGa_1-xAs/In_0.15Ga_0.85As/GaAs quantum wells (DWELL structures) as a function of the In content x (x=0.10-0.25) in the capping In_xGa_1-xAs layer. Photoluminescence (PL) study reveals the red shift of QD ground state peak when x increases from 0.10 to 0.15. The significant degradation of PL intensity is monitored together with a blue shift of PL peaks and PL band broadening when x = 0.20 or 0.25. The fitting procedure has been applied on the base of Varshni analysis to PL peaks. It is shown that all DWELL structures are characterized by the same Varshni parameters that are close, but not equal, to the band gap shrinks with temperature in the bulk InAs. The last fact testifies that in studied DWELL structures the process of In/Ga intermixture between QDs and a capping layer takes place partially. However this process cannot explain the difference in PL peak positions. This difference, apparently, related to the different levels of elastic strain in DWELLs that change non monotonically due to the variation of In concentrations in capping layers.