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) cm(-2) has been grown by molecular beam epitaxy (MBE) at a substrate temperature of 590 degrees C. To promote an ordered incorporation and thus avoid c lustering of Si atoms, vicinal GaAs(001) surfaces 2 degrees misoriente d towards (111)Ga were used and Si was supplied in pulses. As evidence d by real-time reflection high-energy electron diffraction (RHEED) mea surements an ordered incorporation of Si atoms on Ga sites along the s tep edges takes place. Although the ordered (3 X 2) structure degrades at high coverages, unusual high sheet carrier concentrations are obta ined by pulsed delta-doping for doping concentrations > 10(13) cm(-2), 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 occu pancy.