InAs/GaAs quantum dot structures emitting in the 1.55 ?m band

We investigated different capping layers covering InAs quantum dot structures grown on GaAs substrates by metalorganic vapor phase epitaxy in order to receive strong photoluminescence at 1.55 mm. Atomic force microscopy showed that uncovered InAs quantum dots are 4-5 nm high lenses with a broad luminescence peaking at 1.43 mm. The GaAs capping improves the quantum dot homogeneity but quantum dot dissolution causes blue shift of emitted light. On the other hand, proper engineering of InGaAs strain reducing layer allows to shift the photoluminescence maximum to 1.55 mm. Analysis of photoluminescence and microscopy data supported by calculation of quantum dot electron states shows that this is caused both by the change of the electronic-barrier structure and by the increase of the height of the overgrown quantum dots.