A complete comprehension of InGaAs capping layer deposition on InAs quantum dots by comparison of simulations, luminescence and X-ray diffraction

Abstract

The mechanism of incorporation of InGaAs capping layer on InAs Quantum dots (QDs) are unclear in most of the literature studies. Various studies suggest vertical strain relaxation to be the cause of the longer wavelength emission of the dots. On the other hand, some suggest preferential In segregation on the periphery of QDs to be the reason for the enhancement of the dot size. In this study, the strain profile, electronic bands, and eigenstates of InAs QDs, with various InGaAs capping layer thickness, have been simulated using nextnano3 software. Further, the structures are grown by a molecular beam epitaxy (MBE) system. Comparison of ground-state emission energy obtained from PL and simulations, proves that strain relaxation alone is not sufficient to explain the shift in the emission wavelength, and indicate presence of a growth mechanism which alters the size of the QDs. From the in-plane and out-plane High-Resolution X-Ray Diffraction (HR-XRD) results, we have explained the complete dynamics involved in the InGaAs capping deposition, which was unclear in the literature up-to-date. Advantages of incorporation of InGaAs capping on the dots, like decrease in strain and defects, preservation of In, and increased activation energy are also observed in the study.