Optical properties of wetting layers in stacked InAs/GaAs quantum dot structures

The optical transitions of the wetting layers in two-fold self-assembled InAs/GaAs quantum dot samples are studied as a function of GaAs spacer thickness by various methods. The absorption related studies by photoreflectance and selective photoluminescence excitation spectroscopy reveal already for thick barriers, for which coupling effects can be excluded, two energetically separated heavy-hole transitions. This splitting indicates the formation of two wetting layers during growth with a 10% difference in width and reflects strain field interaction between the island layers. Thin spacer layer samples show in addition the expected wetting layer coupling as confirmed by subband calculations.