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.