Effect of exciton transfer on recombination dynamics in vertically nonuniform GaAsSb epilayers

Low-temperature photoluminescence (PL), photoreflectance (PR), and temperature dependent time-resolved PL spectroscopies are employed to investigate optical emission processes and exciton dynamics in graded GaAsSb epilayers. The nonuniformity in the Sb composition along the growth direction is disclosed by low-temperature PL and PR measurements. Furthermore, significant differences in PL dynamics are found at low temperatures for the PL emissions originating from spatial regions with the low and high Sb compositions, with a fast decay and a slow rise at the early stage of the PL transient, respectively. This finding is attributed to exciton transfer from the low Sb region to the high Sb region. The obtained results are important for a general understanding of optical transitions and exciton/carrier dynamics in material systems with a graded alloy composition.Funding Agencies|National Natural Science Foundation of China [61274141, 11874377]; Shanghai Science and Technology Foundation [18JC1420401]; Natural Science Foundation of Shanghai [18ZR1445700]; China Scholarship Council [201604910582]