Formation of strain reduced In0.54Al0.34Ga0.12As layer of vertically coupled QDs arrays for O-band telecom single photon sources

Abstract

We demonstrate the correlative research on the multi-stacked vertically coupled InAs quantum dots (VCQDs) capped by 15 nm combinational capping layer of In(0.21)Al(0.21)Ga(0.58)As and GaAs layer through Atom probe tomography (APT), Transmission Electron Microscopy (TEM), Secondary Ion Mass Spectroscopy (SIMS), High-Resolution X-Ray Diffraction (HRXRD) and Reciprocal Space Mapping (RSM). From the comparative studies, we observed a strain reduction of ∼ 2.3 ± 0.05% in the system, leading to the formation of strain-reduced (SR) In0.54Al0.34Ga0.12As layer with a lattice constant of 5.88 Å, which will work as a shielding layer. We found that the middle portion of the 3rd to 8th layer QDs structure was constant in size, shape, composition, and density, which enhances the carrier confinement in QDs. The computed strain energy values contributed to the overall growth structure of the 30 - layers VCQDs were recorded to be 2.2 meV/atoms. We report the detailed analogy of the in-out flow of In/Ga adatoms in the In0.54Al0.34Ga0.12As layer leading to the evolution of fully developed bigger InAs QDs size. To support the APT results, we also present the outcomes studies of the HRXRD Out-plane and In-Plane symmetric RSM experiment at (002), (004), and (006) reflections to investigate the compressive strain contribution in the SR In0.54Al0.34Ga0.12As shielding layer. This 30-layer VCQDs structure can be employed to fabricate high thermal stability operating at 1.3 µm O-band telecom Single Photon Sources (SPSs).