Lateral inhomogeneities in engineered Schottky barriers

We have measured the lateral homogeneity in Al/GaAs(0 0 1) Schottky barriers engineered for low barrier height through fabrication of a Si layer at the interface under As flux. We used a spectroscopic photo emission and low-energy electron microscope (SPELEEM) which combines a low-energy electron microscope with an imaging band pass filter to allow spatially resolved synchrotron radiation photoemission experiments. As-grown samples with a Si interlayer thickness of 0.5 and 3 monolayers appeared homogeneous within the spatial resolution of the SPELEEM (22 nm). Annealing an Al/Si(As)/GaAs(0 0 1) heterostructure for 10 min at 500 degrees C, however, caused inhomogeneous As outdiffusion which is correlated with a local As 3d core level shift of 0.3 eV. We suggest that the reported degradation of such engineered Schottky barriers might be correlated with laterally inhomogeneous As out-diffusion upon annealing.