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-gro wn Be:GaAs delta-doped layers with atomic resolution. These were obtai ned using cross-sectional scanning tunneling microscopy. At low Be are al density, the width of the delta layers is 1 nm, whereas at higher B e areal densities the spread of the layers is appreciable and the widt hs are approximately 5 nm. This spreading is mostly symmetric around t he intended position of the delta-doped layer, and is ascribed to drif t resulting from the Coulombic repulsion between the ionized dopants a t growth temperature. Structure in the spatial distribution of dopants within the delta layer also reflects this repulsion.