Be Delta-Doped Layers in GaAs Imaged with Atomic Resolution Using Scanning Tunneling Microscopy.

We present first results of the analysis of molecular beam epitaxy-grown Be:GaAs delta-doped layers with atomic resolution. These were obtained using cross-sectional scanning tunneling microscopy. At low Be areal density, the width of the delta layers is 1 nm, whereas at higher Be areal densities the spread of the layers is appreciable and the widths are approximately 5 nm. This spreading is mostly symmetric around the intended position of the delta-doped layer, and is ascribed to drift resulting from the Coulombic repulsion between the ionized dopants at growth temperature. Structure in the spatial distribution of dopants within the delta layer also reflects this repulsion.