Metamorphosis of self-assembled InAs quantum dot through variation of growth rates

Abstract

This study investigates the metamorphosis of self-assembled InAs quantum dots (QDs) by varying the InAs growth rate in the range of 0.025–0.15 ML/s. The theoretical approaches for calculating the shape transformation from pyramidal QDs to truncated pyramidal QDs with symmetric/asymmetric slant heights and their outcomes are presented. The cut-off height from the tip of the pyramidal QDs depends on many compression factors, such as thickness of the spacer layer, InAs growth rate, and QD density. From high resolution transmission electron microscopy (HRTEM) images, it was affirmed that the slant heights of the truncated pyramidal QDs were symmetrical and evenly compressed at lower growth rates. However, this is in contrast with the high growth rates, where there is formation of asymmetrical slant heights of the truncated pyramidal QD in conjunction with high randomness in dot size dispersion. We explore the complete metamorphosis of self-assembled QDs in detail along with the effect of growth rate variation. The five different shaped QDs with different aspect ratio (as a result of growth rate variation) were able to tune the emission wavelength from 1201 nm to 1261 nm, which might be applicable for high compact multimode laser diode. Furthermore, we report for the first time on structural characteristics of the metamorphosis of self-assembled InAs QDs through In-plane reciprocal space mapping. The diffused scattering peak from In/Ga intermixing were intensified for high growth rate, indicating diffusion of Ga adatoms into InAs QDs. The hybrid work of experimental and simulations prove that the truncated pyramidal QDs with symmetrical slant heights is important for achieving longer wavelength in comparison with truncated pyramidal QDs with asymmetrical slant heights. It is also shown that the electron confinement is stronger in low growth rate in comparison to the high growth rate. Moreover, calibration of the InAs growth rate is essential as it determines how the next-level vertical multi-stacked strain-coupled InAs QD heterostructures could be designed, in order to meet the state-of-the-art performance of the QD based multimode laser diode.