Observation of monolayer-splitting for InAs/GaAs quantum dots

A pronounced modulation is observed in the photoluminescence (PL) spectrum of self-organized InAs/GaAs quantum dots (QDs), recorded at low excitation densities. The clearly distinguishable peaks are identified as a multimodal distribution of the ground state transition energy, originating from a discrete, stepwise variation of the structural properties of the QDs, which is associated with an increase of the QD height in monolayer (ML) steps. The observation of a ML splitting implies a flat QD shape with well-defined upper and lower interfaces as well as negligible indium segregation. The electronic properties of the InAs/GaAs QDs were investigated by PL and PL-excitation spectroscopy and are discussed based on realistic calculations for flat InAs/GaAs QDs with a truncated pyramidal shape based on an extended 8-band k·p model. The calculations predict a red shift of the ground state transition with each additional ML, which saturates for heights above 9 ML, is in good agreement with experiment.