Schottky enhancement of contacts to n-GaAs via the exchange mechanism using NiAlxGa1-x as a metallization

Based on the thermodynamic/kinetic model of the exchange mechanism, the ter nary intermetallic compound NiAlxGa1-x (where 0 < x less than or equal to 1 )was identified as a metallization that may be used to fabricate Schottky e nhanced contacts to n-GaAs. Experimental: phase equilibrium:studies of the quaternary Al-Ga-Ni-As system, in conjunction with diffusion data available in the literature, indicated that the phase NiAlxGa1-x fulfills the thermo dynamic and kinetic requirements necessary for participation in an exchange reaction with GaAs. Contacts to n-GaAs were fabricated by sputter depositi on of NiAlxGa1-x metallizations, with compositions corresponding to x = 0.0 0, 0.25, 0.50, 0.75 and 1.00. These contacts were subjected to rapid therma l processing, and analyzed using cross-sectional high resolution transmissi on electron microscopy and I-V characterization. Electron microscopy and co ncomitant electron dispersive spectroscopic analysis indicated that a very thin (2.5 nm) interfacial region of AlxGa1-xAs was formed in annealed conta cts for which x > 0.00, in accordance with the exchange mechanism model. Sc hottky barrier enhancement was also observed in all annealed contacts for w hich x > 0.00. The degree of Schottky barrier enhancement was shown to be d ependent upon the initial composition of the metallization, again in,accord ance with the prediction of the exchange mechanism model. Schottky barrier heights as high:as 0.96 eV were obtained under the optimum annealing condit ions of 400 degrees C for 1 min. However, these experimentally determined S chottky barrier heights were somewhat smaller than the values that were ant icipated based upon the exchange mechanism model. Potential reasons for the se discrepancies were discussed. Overall, it was demonstrated that the ther modynamic/kinetic model of the exchange mechanism is a powerful tool for id entifying metallizations that may be used to enhance the Schottky barriers of contacts to n-GaAs. (C) 1999 American Vacuum Society. [S0734-211X(99)046 02-8].