Ⅲ-Ⅴ compound semiconductor materials grown on elemental semiconductor substrates have attracted much attention due to their high mobility and direct bandstructure.And the Ⅲ-V/Si system could combine the advantages of both material systems.The growth of high quality Ⅲ-Ⅴ thin films on Si(or Ge)is the fist crucial step for Ⅲ-Ⅴ high-mobility or optical devices.We investigate the Ⅲ-V/Si system by large area growth and aspect ratio trapping(ART)method.Device-quality GaAs thin films have been grown on miseut Ge-on-Si substrates by metal-organic chemical vapor deposition(MOCVD).A method of two-step epitaxy of GaAs is performed to achieve a high-quality top-layer.The initial thin buffer layer at 360 ℃ is critical for the suppression of anti-phase boundaries and threading dislocations.Etch pit density of GaAs epilayers by KOH etching could reach 2.3 × 105 cm-2 and high-quality GaAs top epilayers are observed by transmission electron microscopy.The root-mean-square roughness of GaAs surface could be less than 1 rim,which is comparable with that of homo-epitaxial GaAs.These low-defect and smooth GaAs epilayers on Si are desirable for GaAs-based devices on silicon substrates.Furthermore,high-quality Ⅲ-Ⅴ material,such as GaAs,InP,InGaAs,and InAs,are grown in nanoscaled V-shaped SiO2 trenches on Si(001)substrates by ART method.GaAs and InP thin films are deposited via MOCVD using a two-step growth process.Threading dislocations arising from lattice mismatch are trapped by SiO2 sidewalls,and antiphase domains boundaries(APBs)are restricted.Based on GaAs and InP buffers,InGaAs QWs and InAs layer are obtained.This approach shows great promise for the nanoscaled Ⅲ-Ⅴ devices on Si.These two methods are promising approaches for high-mobility or optoclectronic devices on Si substrates.