Localized and delocalized states at the band gap in heteroepitaxial GaAs grown on Si

There exist the interfacial mismatch strains and high density structural de fects in heteroepitaxial GaAs grown on Si (GaAs/Si) because of a large misf it of the lattice constants and a large difference in linear thermal expans ion coefficient between GaAs and Si materials. Our experiments show that th e disordering in GaAs/Si epilayers strongly depends on their growth conditi on, especially on the concentration ratio [As]/[Ga] and demonstrate that at [As]/[Ga]=20 to 40 the relationship of temperature versus intensities of t he dominant photoluminescence (Pt) peaks, related to the delocalized states at the band gap of GaAs/Si, satisfies an Arrhenius equation to determine t he thermal activation energies of delocalized states and at [As]/[Ga] great er than or equal to 50 the relationship of temperature versus intensities o f the dominant PL peaks, related to the localized states, satisfies an equa tion valid for amorphous semiconductors to determine the characteristic tem peratures of localized states reflecting the disorder degree in GaAs/Si epi layers.