Metamorphic InAs/InAlAs/InGaAs quantum dots: Establishing the limit for indium composition in InGaAs buffers

Metamorphic InAs/InAlAs/InGaAs quantum dots (QDs) are very interesting nanostructures for redshifting the emission of zero-dimensional carriers towards the infrared telecom C-band at 1.55 μm. In this work, we present a study of InxGa1–xAs/In1–yAlyAs/InAs/In1–yAlyAs/InxGa1–xAs metamorphic QD heterostructures where InAlAs barriers were inserted above and below QDs in order to increase carrier confinement and reduce their thermal escape. Samples with x = 0.45 and 0.50 and y = 0.60 and 0.70 are studied using photoluminescence and photocurrent spectroscopies. The modelization of the quantum system allows us to discuss properties and features of these nanostructures. On the basis of experimental results and theoretical calculations, we conclude that x = 0.45 is an intrinsic limit for the In composition in metamorphic buffers, as, for x = 0.50, electrons are not confined in QDs and quantum light emission is not feasible anymore. We are then able to conclude that metamorphic QDs have an intrinsic limit in redshifting the emission beyond 1.65 μm, due to the complete loss of electron confinement that adds to the deleterious rise of density of extended defects in the structures caused by the increase of the In composition in InGaAs metamorphic buffer.