Selective MOCVD growth of single-crystal dense GaAs quantum dot array using cylinder-forming diblock copolymers

In order to realize the theoretical advantages of ideal quantum dots (QDs) (i.e., complete three-dimensional carrier confinement), an alternate approach to self-assembly has been investigated for elimination of the wetting layer and achieving a uniform mono-modal QD size distribution. On a GaAs substrate, hexagonally arranged uniform-sized QD arrays have been fabricated. The QD patterning is prepared by dense nanoscale diblock copolymer lithography, which consists of perpendicularly ordered cylindrical domains of polystyrene-block-poly(methylmethacrylate) (PS-b-PMMA) matrix. The polymer patterns are transferred to a dielectric template mask and then single-crystal GaAs QDs are selectively grown on the patterned substrate by metalorganic chemical vapor deposition (MOCVD). Single-crystal QDs are confirmed by X-ray diffraction with a large area detector. Scanning electron mocroscope images indicate that the QD density is larger than 5×1010/cm2, comparable to Stranski–Krastnow growth mode. Using the technique of diblock copolymer lithography followed by the selective MOCVD growth of the QDs, a higher degree of control of QD shape, size uniformity, and composition is expected.