Selective epitaxy of III-V semiconductor on Si substrates patterned by diblock copolymer*

III-V semiconductors, GaAs and InAs, were grown on Si substrates using molecular beam epitaxy. Si substrates were patterned with SiO$_{2}$ using thin films of diblock copolymer, PS-$b$-PMMA. Using a thin film of a random P(S-r-MMA) copolymer to balance interfacial interactions, spin coated film of PS-b-PMMA, having cylindrical microdomains, were annealed 170$^{o}$C to orient the microdomais normal to the surface.[ P. Mansky et al, Science, 275, 1997 (1458)] After removal of the PMMA cylinders, RIE was used to transfer the copolymer template to the substrate yielding a hexagonal array of $\sim $20 nm pores in the substrate. GaAs and InAs were selectively filled in pores. Images from scanning electron microscopy show that GaAs and InAs quantum dots with density of 8$\times $10$^{10}$ cm$^{-2}$ and diameter of 30nm were achieved by selective epitaxy. This provides the possibility of patterning of nanostructures for integration of III-V materials on Si and offers new potentials for electronic and optoelectronic applications based on regular or homogeneous structures.