Structural properties of graded InxGa1-xAs metamorphic buffer layers for quantum dots emitting in the telecom bands

In recent years, there has been a significant increase in interest in tuning the emission wavelength of InAs quantum dots (QDs) to wavelengths compatible with the already existing silica fiber networks. In this work, we develop and explore compositionally graded InxGa1-xAs metamorphic buffer layers (MBLs), with lattice constant carefully tailored to tune the emission wavelengths of InAs QDs towards the telecom O-band. The designed heterostructure is grown by molecular beam epitaxy (MBE), where a single layer of InAs QDs is grown on top of the MBL and is capped with a layer having a fixed indium (In) content. We investigate the structural properties of the grown MBLs by reciprocal space mapping, as well as transmission electron microscopy, and verify the dependence of the absorption edge of the MBL on the In-content by photothermal deflection spectroscopy measurements. This allows us to identify a growth temperature range for which the MBLs achieve a near-equilibrium strain relaxation for In-content up to ∼30%. Furthermore, we explore the emission wavelength tunability of QDs grown on top of a residual strained layer with a low density of dislocations. Specifically, we demonstrate a characteristic red-shift of the QD photoluminescence towards the telecom O-band (1300 nm) at low temperature. This study provides insights into the relaxation profiles and dislocation propagation in compositionally graded MBLs grown via MBE, thus paving the way for realizing MBE-grown heterostructures containing InAs QDs for advanced nanophotonic devices emitting in the telecom bands.