BE DELTA-DOPED LAYERS IN GAAS STUDIED BY SCANNING-TUNNELING-MICROSCOPY

We have imaged Be delta-doped layers in GaAs with atomic resolution us ing cross-sectional scanning tunnelling microscopy. In the samples gro wn at low temperature (480 degrees C) we observe that the width of dop ing layers for concentrations up to 1 x 10(13) cm(-2) is Smaller than 1 nm, while for a higher doping concentrations we find that the doping layer thickness increases strongly with doping concentration. This br oadening is symmetrical about the intended doping plane. We believe th at this broadening of the doping layer al high doping concentrations i s 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.