MAPPING OF ALXGA1-XAS BAND EDGES BY BALLISTIC-ELECTRON-EMISSION SPECTROSCOPY

We have employed ballistic electron emission microscopy (BEEM) to stud y the energy positions in the conduction band of AlxGa1-xAs. Epilayers of undoped AlxGa1-xAs were grown by molecular beam epitaxy on conduct ive GaAs substrates. The Al composition x took on values of 0, 0.11, 0 .19, 0.25, 0.50, 0.80 and 1 so that the material was examined in both the direct and indirect band gap regime. The AlxGa1-xAs layer thicknes s was varied from 100 to 500 Angstrom to ensure probing of bulk energy levels. Different capping layers and surface treatments were explored to prevent surface oxidation and examine Fermi level pinning at the c ap layer/AlxGa1-xAs interface. All samples were metallized ex situ wit h a 100 Angstrom Au layer so that the final BEEM structure is of the f orm Au/capping layer/AlxGa1-xAs/bulk GaAs. Notably we have measured th e Schottky barrier height for Au on AlxGa1-xAs. We have also probed th e higher lying band edges such as the X point at low Al concentrations and the L point at high Al concentrations, Variations of these critic al energy positions with Al composition x were mapped out in detail an d compared with findings from other studies, Local variations of these energy positions were also examined and found to be on the order of 3 0-50 meV. The results of this study suggest that BEEM can provide accu rate positions for multiple energy levels in a single semiconductor st ructure. (C) 1997 American Vacuum Society.