The use of GaAsSbN capping layers on InAs/GaAs quantum dots (QDs) has recently been proposed for micro- and optoelectronic applications for their ability to independently tailor electron and hole confinement potentials. However, there is a lack of knowledge about the structural and compositional changes associated with the process of simultaneous Sb and N incorporation. In the present work, we have characterized using transmission electron microscopy techniques the effects of adding N in the GaAsSb/InAs/GaAs QD system. Firstly, strain maps of the regions away from the InAs QDs had revealed a huge reduction of the strain fields with the N incorporation but a higher inhomogeneity, which points to a composition modulation enhancement with the presence of Sb-rich and Sb-poor regions in the range of a few nanometers. On the other hand, the average strain in the QDs and surroundings is also similar in both cases. It could be explained by the accumulation of Sb above the QDs, compensating the tensile strain induced by the N incorporation together with an In-Ga intermixing inhibition. Indeed, compositional maps of column resolution from aberration-corrected Z-contrast images confirmed that the addition of N enhances the preferential deposition of Sb above the InAs QD, giving rise to an undulation of the growth front. As an outcome, the strong redshift in the photoluminescence spectrum of the GaAsSbN sample cannot be attributed only to the N-related reduction of the conduction band offset but also to an enhancement of the effect of Sb on the QD band structure.

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This work analyses the Bi incorporation in InAs1-xBix/InAs(100) epilayers grown by MBE through advanced transmission electron microscopy techniques. Samples grown from 350–400 °C resulted in Bi contents <3.3% exhibiting compositional variation in the growth direction. In contrast, roughly spherical clusters appeared in the sample grown at lower temperatures. The clusters are made up of the binary InBi with a tetragonal PbO phase surrounded by a matrix of InAs0.95Bi0.05 indicating the Bi solubility limit in InAs. These InBi crystals underwent a cubic distortion and are tilted 55° with regard to the InAsBi matrix. The crystallographic relationships are analysed in detail.

The distribution of bismuth in InAs1-xBix/GaAs quantum dots is analyzed by atomic-column resolution electron microscopy and imaging simulation techniques. A random Bi distribution is measured in the case of <0.03 ML/s Bi flux during the InAs growth with no significant variations in the shape or size of quantum dots, resulting in a low redshift and the degradation of the photoluminescence. However, for a 0.06 ML/s Bi flux the lateral indium segregation into the quantum dots is enhanced and Bi is incorporated inside them. As a result, a strong redshift and an increase of the peak intensity are found in this sample.

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