Coalescence of planar GaAs nanowires into strain-free three-dimensional crystals on exact (001) silicon

•Coalescence of GaAs from nanowires on V-grooved Si led to 3D disk-shaped crystals.•The GaAs disks on Si exhibited smooth top surface free of antiphase boundaries.•Superior material properties over GaAs films on planar offcut Si were uncovered.•The residual stress in GaAs induced by the thermal mismatch was studied by PL.•Strain-free micro-sized GaAs disks can be achieved by decreasing the crystal size.

We report three dimensional (3D) disk-shaped GaAs crystals on V-groove patterned (001) Si substrates by metalorganic chemical vapor deposition. Planar GaAs nanowires with triangular cross-sections were grown inside Si V-grooves by nano-scale selective heteroepitaxy. These nanowires were then partially confined in micro-sized SiO2 cavities and coalesced into uniform arrays of 3D crystals. Scanning electron microscope and atomic force microscopy inspection showed the absence of antiphase-domains and smooth top surface morphology. Superior structural and optical properties over GaAs thin films on planar Si were also demonstrated. More remarkably, by growing the 3D crystals on V-grooved Si, we were able to overcome the residual tensile stress induced by the thermal mismatch between GaAs and Si. Strain-free GaAs was uncovered in the crystals with a dimension of 3×3 µm2.