Relationship between Barrier Thickness and Crystal Quality in InGaAs/InGaAsP Strained Multi-Quantum Well Structure

The barrier layer thickness dependence on crystal quality of the multi-quantum well (MQW) structure with compressively strained InGaAs wells and InGaAsP (λg=1.15 µm) barriers is investigated. The lattice mismatch Δa/a for a 15-period MQW structure with a 1%-strained 5 nm InGaAs (In0.68Ga0.32As) well layer is improved by increasing the thickness of the barrier layer, and it becomes saturated over 15 nm to around 0.2%. The X-ray diffraction peak intensity becomes saturated over 10 nm. The strongest exciton peak intensity and the sharpest peak width are observed for a 10 nm barrier. The optimum well volume ratio for a MQW, shown as W/(W+B), is around 0.3 from the results of the X-ray diffraction peak intensity and the exciton peak width and intensity (W: well thickness, B: barrier thickness).