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

Abstract

Delta-doped GaAs: Si with doping densities up to 4 × 10 14 cm −2 has been grown by molecular beam epitaxy (MBE) at a substrate temperature of 590°C. To promote an ordered incorporation and thus avoid clustering of Si atoms, vicinal GaAs(001) surfaces 2° 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 × 2) structure degrades at high coverages, unusual high sheet carrier concentrations are obtained 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 related to segregation effects as well as to a modification of the site occupancy.