Cross-sectional AFM of GaAs-based multilayer heterostructure with thin AlAs marks

In this work we report the experimental results on AFM analysis of cleavages of multilayer GaAs−based heterostructures. Additional thin AlAs layer was introduced as a mark at the border of every main (thick) layer during the growth process in order to visualize the boundary. AlAs is expected to be a suitable mark−layer for GaAs−based structure. First, the lattice parameter of AlAs is very close to that of GaAs. Mark layer has therefore an epitaxial pseudomorphic growth mode, as well as the next layer grown over the mark. Second, natural oxidation is used as essential technological step. As previously reported in [1], oxidized AlGaAs layer on the cleavage of AlGaAs/GaAs structure is higher than neighboring GaAs layers. Hence, the boundary is seen as a wall in the cross−sectional AFM image. Finally, the sample preparation procedure is simpler in comparison with other techniques. An atomically flat cleavage surface of GaAs crystal perpendicular to (001) crystal plane arises from a perfect (110) cleavage plane in the zinc−blend type crystal.