Title : Comparative of different capping approaches in the preservation of InAs/GaAs quantum dots in terms of content, size and density
Self-assembled InAs/GaAs quantum dots (QDs) fabricated by the Stranski-Krastanov epitaxial growth mode have attracted great interest due to their enormous potential in a wide range of optoelectronic applications such as lasers or solar cells. The emission properties of these QDs are very sensitive to their size, shape, deformation state, density and composition, so precise control of the capping process is necessary to avoid significant modifications of the QDs due to different phenomena such as intermixing, segregation, etc. In general, two different capping strategies have been widely used (i) by changing the nature of the capping layers (CL), e.g., using compressive GaAsSb layers, and (ii), altering the growth kinetics during capping by reducing the surface diffusion, e.g., controlling the growth rate. In this work, a comprehensive structural and optical analysis has been performed to describe the InAs/GaAs QDs system using both capping strategies, by combining different transmission electron microscopy (S)TEM techniques and photoluminescence (PL) measurements. Changes in the mean volume, composition and density of the capped QDs covering a statistically significant number of buried QDs were performed, along with wetting layer (WL) analyses for each strategy. We have observed that faster growth rates and increased Sb content reduce the decomposition of QDs, but act differently. From the comparison, 3 important conclusions have been drawn: (i) QD volume measurement is a better parameter than QD height for assessing QD decomposition and photoluminescence redshift, (ii) higher QD volume is not always related to higher In content and (iii) increasing the average volume of QDs leads to a reduction of the QD density. As we will show, the three parameters are connected, albeit with significant differences for each strategy.
Audience Take Away:
- The audience will be able to use this work to discover the enormous opportunities offered by new aberration-corrected STEM techniques in the analysis of nanostructured materials.
- They will have access to a useful information on the parameters for the design of new self-assembled nanostructures based on InAs/GaAs quantum dots (QDs), which are crucial for developing optimal optoelectronic devices.
- The mechanism and effects of two different capping strategies to protect the integrity of InAs/GaAs QD have been compared in this work: the growth rate of CL and the use of SRL with Sb. Comparison allows to conclude that faster growth rates and SRL with Sb reduce QD decomposition, although with significant differences.