Atomic-scale controlled incorporation of ultrahigh-density Si doping sheets in GaAs

Delta-doped GaAs: Si with doping densities up to 4 X 10(14) square centimetre has been grown by molecular beam epitaxy (MBE) at a substrate temperature of 590 degree. To promote an ordered incorporation and thus avoid clustering of Si atoms. vicinal GaAs(O01) surfaces 2 degree misoriented towards (111)Ga were used and Si was supplied in pulses. As evidenced by real-time reflection high-energy electron diffraction (RHEED) measurements an ordered incorporation of Si atoms on Ga sites along the step edges takes place. Although the ordered (3 x 2) structure degrades at high coverages, unusual high sheet carrier concentrations are obtained by pulsed delta-doping for doping concentrations > 10(13) square centimetre , as revealed by Hall measurements. The surface conditions during GaAs overgrowth have a strong influence on the free electron concentration. too. Raman scattering by local vibration modes and secondary ion mass spectrometry (SIMS) measurements are used to show that this is relate d to segregation effects as well as to a modification of the site occupancy.