Influences of strain and phase separation on the alignment characteristics of five-stacked InAs/lnAIGaAs quantum dots grown on InP(001)

This paper reports the influence of the thickness of the InAlGaAs spacer on the formation characteristics of five-stacked In As quantum dots (QDs) grown on InAlGaAs/InP. The emission wavelength for the five-stacked In As QD layers separated by a 5-nm-thick InAlGaAs spacer was 1.526 μm. As the spacer thickness was increased, the emission wavelength was at first red-shifted to 1.550 μm and remained constant thereafter. Also, the carrier lifetime of the In As QDs increased with increasing spacer thickness. The variations in the emission wavelength and in the carrier lifetime with the spacer thickness are most likely due to the change in the QD formation, as confirmed by transmission electron microscopy (TEM). The TEM images indicated that the influence of the accumulation of strain from the bottom QD layer on the formation of the upper QD layer, when a relatively thin spacer was used, was more important than the intrinsic phase separation of InAlGaAs. However, the intrinsic phase separation of the InAlGaAs layer became increasingly dominant as the spacer thickness was increased.