Morphology and Optical Properties of Self-Assembled In_0.5Ga_0.5As Quantum Dots with Different Spacer Layer Thickness

Uncapped double stacked In_0.5Ga_0.5As quantum dots (QDs) with different spacer layer thicknesses were grown using metal-organic chemical vapour deposition (MOCVD). The precursors used for the growth of the GaAs layer and In_0.5Ga_0.5As QDs were trimethylgallium (TMGa), trimethylindium (TMIn), and arsine (AsH₃). The morphology and optical properties of the self-assembled In_0.5Ga_0.5As QDs were investigated and characterized using atomic force microscopy (AFM) and photoluminescence (PL). The AFM images revealed that the sizes of the dots on the topmost were not uniformly distributed. The average size of the dots fluctuated as the GaAs spacer layer thickness increased. A room temperature PL measurement was used to establish the quality and quantity of the stacked QDs. The PL peak position remained at 1148 nm for all samples of QDs; however, the PL intensity increased as spacer layer thickness increased. The structure of the spacer layer in the stacked QD affected the morphology of the topmost surface of the QDs. The PL measurement coherently reflected the AFM characterization, in which the strong PL spectra were caused by the uniformity and high density of the QDs. The surface morphology, structure, and optical properties of the stacked QDs are attributed to seed-layer (first layer) formation of dots and spacer layer structures.