On the origin of carrier localization in AlInAsSb digital alloy

We compared the photoluminescence (PL) properties of AlInAsSb digital alloy samples with different periods grown on GaSb (001) substrates by molecular beam epitaxy. Temperature-dependent S-shape behavior is observed and explained using a thermally activated redistribution model within a Gaussian distribution of localized states. There are two different mechanisms for the origin of the PL intensity quenching for the AlInAsSb digital alloy. The high-temperature activation energy E₁ is positively correlated with the interface thickness, whereas the low-temperature activation energy E₂ is negatively correlated with the interface thickness. A quantitative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) study shows that the interface quality improves as the interface thickness increases. Our results confirm that E₁ comes from carrier trapping at a state in the InSb interface layer, while E₂ originates from the exciton binding energy due to the roughness of the AlAs interface layer.