Impact of MBE-grown (In, Ga)As/GaAs metamorphic buffers on excitonic and optical properties of single quantum dots with single-photon emission tuned to the telecom range

Tuning GaAs-based quantum emitters to telecom wavelengths makes it possible to use existing mature technology for applications in, e.g., long-haul ultrasecure communication in fiber networks. A promising method redeveloped recently is to use a metamorphic (In, Ga)As buffer that redshifts the emission by reducing strain. However, the impact of such a buffer also causes the simultaneous modification of other quantum dot (QD) properties. Knowledge of these effects is crucial for actual implementations of QD-based nonclassical light sources for quantum communication schemes. Here, we thoroughly study single GaAs-based quantum dots grown by molecular-beam epitaxy on specially designed, digital-alloy (In, Ga)As metamorphic buffers. With a set of structures varying in the buffer indium content and providing quantum dot emission through the telecom spectral range up to 1.6 mu m, we analyze the impact of the buffer and its composition on QD structural and optical properties. We identify the mechanisms of quantum dot emission shifts with varying buffer compositions. We also look at charge-trapping processes and compare excitonic properties for different growth conditions with single-dot emission successfully shifted to both the second and third telecom windows.