BERYLLIUM DELTA-DOPING OF GAAS GROWN BY MOLECULAR-BEAM EPITAXY

Spatial localization of Be in δ-doped GaAs within few lattice constants (<20 Å) is achieved at low growth temperatures for concentrations N2DBe <1014 cm-2 as indicated by capacitance-voltage profiles and secondary ion mass spectroscopy. At elevated growth temperatures and at higher Be concentrations, significant spreading of the dopants occurs and is explained by (i) Fermi-level pinning-induced segregation, (ii) repulsive Coulomb interaction of dopants, and (iii) diffusion. The highest Be concentration achieved at low growth temperatures exceeds 2×1020 cm-3 and is limited by repulsive dopant interaction. It is shown that the repulsive Coulomb interaction results in a correlated, nonrandom dopant distribution. The diffusion coefficient of Be in GaAs is determined and is found to be much lower than previously reported.