Improvements of stacked self-assembled InAs/GaAs quantum dot structures for 1.3 μm applications

We propose the growth of thick ‘spacer’ layers (d) for high-quality 10-stack InAs/GaAs quantum dots (QDs) emitting at 1.23 μm without the use of strain reduction layers (SRLs). All samples were grown using molecular beam epitaxy (MBE) and extensively characterised using X-ray diffraction, optical spectroscopy and microscopy techniques. We demonstrate that for d<50 nm, large ‘volcano-like’ defects are formed at the top of the stacked structure, while for d=50 nm, these features were not observed. The process of suppressing these abnormal defects has resulted in significant photoluminescence (PL) enhancement, paving the way for the realisation of defect-free QD laser devices.