Exploring possibilities in AFM studies of InAs/GaAs QDs

Abstract

The main focus of this master thesis work has been to image InAs emph{quantum dots} (QDs) using emph{atomic force microscopy} (AFM), to identify and evaluate various image processing methods used to estimate the volume of the InAs QDs. The InAs QDs studied in this thesis work, had been deposited on GaAs substrates, using solid-source emph{molecular beam epitaxy} (MBE) before the thesis work started. The total QD volume was determined for all samples, using eight different estimation methods. The purpose of estimating the total QD volume, was to compare the total volume to the deposited volume.Previous studies on similar samples, have indicated that the total volume can be larger than the deposited volume during MBE growth. This discrepancy is explained by incorporation of Ga from the substrate during growth. This was not observed in this thesis work. One possible explanation is that the samples have oxidized; resulting in a lower measured height.In addition, the relationship between atomic steps, defects and the appearance of large QDs were studied. parTwo series of samples were studied: one in which the QD growth temperature was varied and one in which the amount of deposited InAs was varied. The total QD volumes were found to increase with the QD growth temperature and the deposited InAs thickness. Square-shaped defects and contours of 2D islands were observed in nearly all samples. Higher/multiple terraces seem to be related to regions of higher QD density.