Localized and Delocalized States at the Band Gap in Heteroepitaxial GaAs Grown on Si

There exist the interfacial mismatch strains and high density structural defects in heteroepitaxial GaAs grown on Si (GaAs/Si) because of a large misfit of the lattice constants and a large difference in linear thermal expansion coefficient between GaAs and Si materials. Our experiments show that the disordering in GaAs/Si epilayers strongly depends on their growth condition, especially on the concentration ratio As/Ga and demonstrate that at As/Ga=20 to 40 the relationship of temperature versus intensities of the dominant photoluminescence (PL) peaks, related to the delocalized states at the band gap of GaAs/Si, satisfies an Arrhenius equation to determine the thermal activation energies of delocalized states and at As/Ga ≥ 50 the relationship of temperature versus intensities of the dominant PL peaks, related to the localized states, satisfies an equation valid for amorphous semiconductors to determine the characteristic temperatures of localized states reflecting the disorder degree in GaAs/Si epilayers.