Optimizing the growth of vertically stacked InP/In0.5Al0.3Ga0.2P quantum dots by metalorganic chemical vapor deposition

Vertically stacked InP self-assembled quantum dots (SAQDs or simply QDs) were grown on In_0.5Al_0.3Ga_0.2P layers lattice-matched to GaAs [001] substrates using metalorganic chemical vapor deposition. Cathodoluminescence (CL) and atomic force microscopy were used to characterize the optical and the morphology properties. We found that, (1) to narrow the CL linewidth, the nominal thickness (i.e., the growth time) of the InP QDs should gradually decrease from the bottom layer to the top one; (2) the CL intensity increases but the surface gets rougher with an increase in the number of QD layers; (3) by inserting an ∼1.5 monolayer thick tensile-strained Al_0.6Ga_0.4P layer in the center of In_0.5Al_0.3Ga_0.2P spacer, the morphology is significantly improved. Using this technique, six-stacked InP/In_0.5Al_0.3Ga_0.2P QDs with good CL properties and smooth surfaces were realized.