BALLISTIC ELECTRON-EMISSION MICROSCOPY STUDIES OF AU-CDTE AND AU-GAAS INTERFACES AND BAND-STRUCTURE

Ballistic electron emission microscopy (BEEM) is an exciting new technique for probing electrical barriers at semiconductor interfaces. It offers huge potential because of its high lateral resolution, which is of the order of 1 nm. We have successfully applied the method to Schottky barriers at Au/n-CdTe and Au/n-GaAs interfaces. Simultaneous imaging of the surfaces of the thin gold overlayers and the metal-semiconductor interfaces shows no correlation between the surface topography and the interface barrier heights. Measured variations in barrier heights are associated with local defects or contamination at the interfaces. On a nanometer scale, the interface barrier heights for the Au-CdTe show large variations (0.7-1.1 eV). We have observed small-scale regions where barrier heights are low. These are probably associated with tellurium precipitates at the interface. By contrast, barrier heights of the Au-GaAs system were exceptionally uniform. These samples were prepared by depositing gold onto atomically clean epitaxially grown GaAs(100) surfaces. Detailed investigations of the voltage dependence of the BEEM current allows the determination of minima in the conduction band of GaAs at the GAMMA, L, and X points.