Evaluation of different capping strategies in the InAs/GaAs QD system: Composition, size and QD density features

Abstract

In this work, two different strategies to preserve InAs/GaAs QDs against decomposition during the capping process have been compared structurally and optically. They are based on: (i) the control of the growth parameters of the capping layer (CL), such as growth rate, and (ii) the nature of the CL, such as the use of GaAsSb strain-reducing layers (SRL). For this, we have statistically determined the average size, composition and areal density in sample populations of dozens of QDs as well as the wetting layer features. Faster growth rates and the presence of Sb in the CL results in an increase of both average QD height as well as the In content but the thorough comparison among all the samples allowed us to draw the following important inferences. i) QD volume is a better parameter than QD height to assess QD decomposition and PL redshift; ii) higher QD volumes are not always linked to higher In contents and iii) a reduction in the QD density is observed in both strategies related to the increase of the average volume. The results are discussed in terms of the mechanisms that might operate during the capping process, such as surface coverage, intermixing or segregation.