STM imaging of Be delta doped layers in GaAs

We have imaged Be delta-doped layers in GaAs with atomic resolution using cross-sectional scanning tunneling microscopy (STM). In the samples, grown at low temperature (480/spl deg/C), we observe that the width of doping layers for concentrations up to 1.10/sup 13/ cm/sup -2/ is smaller than 1 nm, while for higher doping concentrations we find that the doping layer thickness increases strongly with doping concentration. This broadening is symmetrical about the intended doping plane. We believe that this broadening of the doping layer at high doping concentrations is due to Coulombic repulsion between individual Be ions. The effect of Coulombic repulsion can also be observed in the spatial distribution of the dopant atoms in the plane of the doping layer.