Dependence of Sheet Hole Concentrations on Growth Kinetics of a Carbon Doped Electron Beam Heated Graphite Source in GaAs and Al0.3GaD0.7As Films Grown by Solid Source MBE

Abstract

AbstractA series of carbon delta- and uniformly- doped GaAs and Al0.3Ga0.7As films have been grown by solid source Molecular Beam Epitaxy using an electron-beam heated graphite rod as the dopant source. In contrast to heated filament carbon sources, this electron-beam source produces atomic carbon C1, rather than C3 as the predominant species. The purpose of these experiments was to compare measured sheet carrier concentration of delta-doped GaAs and Al0.3Ga0.7As films under fixed growth conditions and with similar carbon beam fluxes using this electron-beam source. The films were characterized by Hall-effect measurements. The Al0.3Ga0.7As films have consistently higher hole sheet carrier concentrations than GaAs films with similar carbon fluxes. Delta-doped Al0.3Ga0.7 As sheet carrier concentrations of up to 2.2×1013 cm−2 were measured, and thin uniformly-doped Al0.3Ga0.7 As carrier densities were measured up to 5.7×1020 cm−3. The uniformly doped Al0.3Ga0.7As films appear to have higher atomic carbon activation than this delta-doped Al0.3Ga0.7As films. These results can be possibly explained in terms of several concurrent processes involving C-C pairing, stronger Al-C bonding, and dopant surface segregation taking place on the growth surface of the delta-doped layer. Photoluminescence intensity measurements of uniformly-doped GaAs shows degradation at hole concentrations greater then 1018 cm−3 and bandgap contraction at hole densities greater than mid 1018 cm−3.